diff --git a/xo-alloc2/idl/GCObject.json5 b/xo-alloc2/idl/GCObject.json5
index 8f7e071f..0b4dfdf9 100644
--- a/xo-alloc2/idl/GCObject.json5
+++ b/xo-alloc2/idl/GCObject.json5
@@ -62,7 +62,7 @@
             doc: ["move instance using allocator"],
             return_type: "Opaque",
             args:[
-                {type: "obj<AAllocator>", name: "mm"},
+                {type: "obj<ACollector>", name: "gc"},
             ],
             const: true,
             noexcept: true,
diff --git a/xo-alloc2/include/xo/alloc2/gc/AGCObject.hpp b/xo-alloc2/include/xo/alloc2/gc/AGCObject.hpp
index ee0703d9..44c777e9 100644
--- a/xo-alloc2/include/xo/alloc2/gc/AGCObject.hpp
+++ b/xo-alloc2/include/xo/alloc2/gc/AGCObject.hpp
@@ -67,7 +67,7 @@ public:
 
     // nonconst methods
     /** move instance using allocator **/
-    virtual Opaque shallow_move(Opaque data, obj<AAllocator> mm)  const  noexcept = 0;
+    virtual Opaque shallow_move(Opaque data, obj<ACollector> gc)  const  noexcept = 0;
     /** during GC: forward immdiate children **/
     virtual size_type forward_children(Opaque data, obj<ACollector> gc)  const  noexcept = 0;
     ///@}
diff --git a/xo-alloc2/include/xo/alloc2/gc/IGCObject_Any.hpp b/xo-alloc2/include/xo/alloc2/gc/IGCObject_Any.hpp
index 000c85fe..25ff5db3 100644
--- a/xo-alloc2/include/xo/alloc2/gc/IGCObject_Any.hpp
+++ b/xo-alloc2/include/xo/alloc2/gc/IGCObject_Any.hpp
@@ -64,7 +64,7 @@ namespace mm {
         [[noreturn]] size_type shallow_size(Copaque)  const  noexcept override { _fatal(); }
 
         // nonconst methods
-        [[noreturn]] Opaque shallow_move(Opaque, obj<AAllocator>)  const  noexcept override;
+        [[noreturn]] Opaque shallow_move(Opaque, obj<ACollector>)  const  noexcept override;
         [[noreturn]] size_type forward_children(Opaque, obj<ACollector>)  const  noexcept override;
 
         ///@}
diff --git a/xo-alloc2/include/xo/alloc2/gc/IGCObject_Xfer.hpp b/xo-alloc2/include/xo/alloc2/gc/IGCObject_Xfer.hpp
index 35e23a62..b311e6f3 100644
--- a/xo-alloc2/include/xo/alloc2/gc/IGCObject_Xfer.hpp
+++ b/xo-alloc2/include/xo/alloc2/gc/IGCObject_Xfer.hpp
@@ -54,8 +54,8 @@ namespace mm {
         }
 
         // non-const methods
-        Opaque shallow_move(Opaque data, obj<AAllocator> mm)  const  noexcept override {
-            return I::shallow_move(_dcast(data), mm);
+        Opaque shallow_move(Opaque data, obj<ACollector> gc)  const  noexcept override {
+            return I::shallow_move(_dcast(data), gc);
         }
         size_type forward_children(Opaque data, obj<ACollector> gc)  const  noexcept override {
             return I::forward_children(_dcast(data), gc);
diff --git a/xo-alloc2/include/xo/alloc2/gc/RCollector.hpp b/xo-alloc2/include/xo/alloc2/gc/RCollector.hpp
index 6192c08d..3bb21468 100644
--- a/xo-alloc2/include/xo/alloc2/gc/RCollector.hpp
+++ b/xo-alloc2/include/xo/alloc2/gc/RCollector.hpp
@@ -52,38 +52,38 @@ public:
     void * alloc_copy_for(const T * src) noexcept {
         return O::iface()->alloc_copy(O::data(), (std::byte *)const_cast<T *>(src));
     }
-    
+
     /** convenience template for move-constructible T (this is common) **/
     template <typename T>
-    void * std_copy_for(const T * src) noexcept {
+    T * std_copy_for(T * src) noexcept {
         void * mem = this->alloc_copy_for(src);
         if (mem) {
             return new (mem) T(std::move(*src));
         }
         return nullptr;
     }
-    
+
     /** forward faceted object pointer in place. Defined in GCObject.hpp to avoid #include cycle **/
     template <typename DRepr>
     void forward_inplace(obj<AGCObject,DRepr> * p_obj);
-    
+
     /** another convenience template for forwarding.
      *  Defined in RGCObject.hpp to avoid #include cycle.
     **/
     template <typename DRepr>
     void forward_inplace(DRepr ** pp_repr);
-    
+
     /** convenience template where pointer requires pivot **/
     template <typename AFacet, typename DRepr>
     requires (!std::is_same_v<AFacet, AGCObject>)
     void forward_pivot_inplace(obj<AFacet,DRepr> * p_obj);
-    
+
     /** add root @p p_root **/
     template<typename DRepr>
     void add_gc_root(obj<AGCObject, DRepr> * p_root) {
         O::iface()->add_gc_root_poly(O::data(), (obj<AGCObject> *)p_root);
     }
-    
+
     /** remove root @p p_root **/
     template <typename DRepr>
     void remove_gc_root(obj<AGCObject, DRepr> * p_root) {
diff --git a/xo-alloc2/include/xo/alloc2/gc/RGCObject.hpp b/xo-alloc2/include/xo/alloc2/gc/RGCObject.hpp
index 1839f83b..673e6e03 100644
--- a/xo-alloc2/include/xo/alloc2/gc/RGCObject.hpp
+++ b/xo-alloc2/include/xo/alloc2/gc/RGCObject.hpp
@@ -60,8 +60,8 @@ public:
     }
 
     // non-const methods (still const in router!)
-    Opaque shallow_move(obj<AAllocator> mm)  noexcept {
-        return O::iface()->shallow_move(O::data(), mm);
+    Opaque shallow_move(obj<ACollector> gc)  noexcept {
+        return O::iface()->shallow_move(O::data(), gc);
     }
     size_type forward_children(obj<ACollector> gc)  noexcept {
         return O::iface()->forward_children(O::data(), gc);
diff --git a/xo-alloc2/src/alloc2/IGCObject_Any.cpp b/xo-alloc2/src/alloc2/IGCObject_Any.cpp
index c9b9329b..a22df0f5 100644
--- a/xo-alloc2/src/alloc2/IGCObject_Any.cpp
+++ b/xo-alloc2/src/alloc2/IGCObject_Any.cpp
@@ -36,7 +36,7 @@ IGCObject_Any::_valid
 // nonconst methods
 
 auto
-IGCObject_Any::shallow_move(Opaque, obj<AAllocator>)  const  noexcept -> Opaque
+IGCObject_Any::shallow_move(Opaque, obj<ACollector>)  const  noexcept -> Opaque
 {
     _fatal();
 }
diff --git a/xo-expression2/include/xo/expression2/DApplyExpr.hpp b/xo-expression2/include/xo/expression2/DApplyExpr.hpp
index 072567c1..b4119def 100644
--- a/xo-expression2/include/xo/expression2/DApplyExpr.hpp
+++ b/xo-expression2/include/xo/expression2/DApplyExpr.hpp
@@ -83,7 +83,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DApplyExpr * shallow_move(obj<AAllocator> mm) const noexcept;
+            DApplyExpr * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DConstant.hpp b/xo-expression2/include/xo/expression2/DConstant.hpp
index da557fc9..e78440ad 100644
--- a/xo-expression2/include/xo/expression2/DConstant.hpp
+++ b/xo-expression2/include/xo/expression2/DConstant.hpp
@@ -63,7 +63,7 @@ namespace xo {
             ///@{
 
             size_t shallow_size() const noexcept;
-            DConstant * shallow_move(obj<AAllocator> mm) const noexcept;
+            DConstant * shallow_move(obj<ACollector> gc) noexcept;
             size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DDefineExpr.hpp b/xo-expression2/include/xo/expression2/DDefineExpr.hpp
index b2cd7ed6..1e20c530 100644
--- a/xo-expression2/include/xo/expression2/DDefineExpr.hpp
+++ b/xo-expression2/include/xo/expression2/DDefineExpr.hpp
@@ -73,7 +73,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DDefineExpr * shallow_move(obj<AAllocator> mm) noexcept;
+            DDefineExpr * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DGlobalSymtab.hpp b/xo-expression2/include/xo/expression2/DGlobalSymtab.hpp
index 9ce29a6e..c6fcdcf1 100644
--- a/xo-expression2/include/xo/expression2/DGlobalSymtab.hpp
+++ b/xo-expression2/include/xo/expression2/DGlobalSymtab.hpp
@@ -43,6 +43,9 @@ namespace xo {
             DGlobalSymtab(dp<repr_type> var_map, DArray * vars,
                           dp<repr_type> type_map, DArray * types);
 
+            /** move constructor (needed because dp<> deletes copy ctor) **/
+            DGlobalSymtab(DGlobalSymtab && other) = default;
+
             /** create instance.
              *  Use memory from @p fixed_mm for @ref map_.
              *  Use memory from @p mm for DGlobalSymtab instance.
@@ -111,7 +114,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DGlobalSymtab * shallow_move(obj<AAllocator> mm) const noexcept;
+            DGlobalSymtab * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DIfElseExpr.hpp b/xo-expression2/include/xo/expression2/DIfElseExpr.hpp
index 1f04ced0..8ffee429 100644
--- a/xo-expression2/include/xo/expression2/DIfElseExpr.hpp
+++ b/xo-expression2/include/xo/expression2/DIfElseExpr.hpp
@@ -99,7 +99,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DIfElseExpr * shallow_move(obj<AAllocator> mm) const noexcept;
+            DIfElseExpr * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DLambdaExpr.hpp b/xo-expression2/include/xo/expression2/DLambdaExpr.hpp
index 58495395..0d8d2391 100644
--- a/xo-expression2/include/xo/expression2/DLambdaExpr.hpp
+++ b/xo-expression2/include/xo/expression2/DLambdaExpr.hpp
@@ -85,7 +85,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DLambdaExpr * shallow_move(obj<AAllocator> mm) const noexcept;
+            DLambdaExpr * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DLocalSymtab.hpp b/xo-expression2/include/xo/expression2/DLocalSymtab.hpp
index dbaad170..b2843cb9 100644
--- a/xo-expression2/include/xo/expression2/DLocalSymtab.hpp
+++ b/xo-expression2/include/xo/expression2/DLocalSymtab.hpp
@@ -98,7 +98,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DLocalSymtab * shallow_move(obj<AAllocator> mm) noexcept;
+            DLocalSymtab * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DSequenceExpr.hpp b/xo-expression2/include/xo/expression2/DSequenceExpr.hpp
index c70f5e72..f876cfac 100644
--- a/xo-expression2/include/xo/expression2/DSequenceExpr.hpp
+++ b/xo-expression2/include/xo/expression2/DSequenceExpr.hpp
@@ -73,7 +73,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DSequenceExpr * shallow_move(obj<AAllocator> mm) const noexcept;
+            DSequenceExpr * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DTypename.hpp b/xo-expression2/include/xo/expression2/DTypename.hpp
index 667082ad..7bd30931 100644
--- a/xo-expression2/include/xo/expression2/DTypename.hpp
+++ b/xo-expression2/include/xo/expression2/DTypename.hpp
@@ -54,7 +54,7 @@ namespace xo {
             ///@{
 
             size_t shallow_size() const noexcept;
-            DTypename * shallow_move(obj<AAllocator> mm) noexcept;
+            DTypename * shallow_move(obj<ACollector> gc) noexcept;
             size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DVarRef.hpp b/xo-expression2/include/xo/expression2/DVarRef.hpp
index 26305923..65abddb2 100644
--- a/xo-expression2/include/xo/expression2/DVarRef.hpp
+++ b/xo-expression2/include/xo/expression2/DVarRef.hpp
@@ -55,7 +55,7 @@ namespace xo {
             ///@{
 
             size_t shallow_size() const noexcept;
-            DVarRef * shallow_move(obj<AAllocator> mm) const noexcept;
+            DVarRef * shallow_move(obj<ACollector> gc) noexcept;
             size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/DVariable.hpp b/xo-expression2/include/xo/expression2/DVariable.hpp
index 1b4f31d2..12abae94 100644
--- a/xo-expression2/include/xo/expression2/DVariable.hpp
+++ b/xo-expression2/include/xo/expression2/DVariable.hpp
@@ -63,7 +63,7 @@ namespace xo {
             ///@{
 
             size_t shallow_size() const noexcept;
-            DVariable * shallow_move(obj<AAllocator> mm) const noexcept;
+            DVariable * shallow_move(obj<ACollector> gc) noexcept;
             size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-expression2/include/xo/expression2/define/IGCObject_DDefineExpr.hpp b/xo-expression2/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
index df303b98..b2c45805 100644
--- a/xo-expression2/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
+++ b/xo-expression2/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DDefineExpr & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DDefineExpr & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DDefineExpr & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp b/xo-expression2/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
index c0b0f35b..75eac694 100644
--- a/xo-expression2/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
+++ b/xo-expression2/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DApplyExpr & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DApplyExpr & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DApplyExpr & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/detail/IGCObject_DConstant.hpp b/xo-expression2/include/xo/expression2/detail/IGCObject_DConstant.hpp
index 35bfbaa2..9cb72026 100644
--- a/xo-expression2/include/xo/expression2/detail/IGCObject_DConstant.hpp
+++ b/xo-expression2/include/xo/expression2/detail/IGCObject_DConstant.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DConstant & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DConstant & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DConstant & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp b/xo-expression2/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
index 5f9cf68e..e7d6fcfd 100644
--- a/xo-expression2/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
+++ b/xo-expression2/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DIfElseExpr & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DIfElseExpr & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DIfElseExpr & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp b/xo-expression2/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
index f44d2ac8..6cf2cd6c 100644
--- a/xo-expression2/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
+++ b/xo-expression2/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DLambdaExpr & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DLambdaExpr & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DLambdaExpr & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp b/xo-expression2/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
index df29b94f..9a9b3f9d 100644
--- a/xo-expression2/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
+++ b/xo-expression2/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DSequenceExpr & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DSequenceExpr & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DSequenceExpr & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/detail/IGCObject_DVarRef.hpp b/xo-expression2/include/xo/expression2/detail/IGCObject_DVarRef.hpp
index d002c5c9..3ca237b6 100644
--- a/xo-expression2/include/xo/expression2/detail/IGCObject_DVarRef.hpp
+++ b/xo-expression2/include/xo/expression2/detail/IGCObject_DVarRef.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVarRef & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVarRef & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVarRef & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp b/xo-expression2/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
index f2a64385..43436ac8 100644
--- a/xo-expression2/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
+++ b/xo-expression2/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DGlobalSymtab & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DGlobalSymtab & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DGlobalSymtab & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp b/xo-expression2/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
index a5c0cd04..c8b9cca1 100644
--- a/xo-expression2/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
+++ b/xo-expression2/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DLocalSymtab & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DLocalSymtab & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DLocalSymtab & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/typename/IGCObject_DTypename.hpp b/xo-expression2/include/xo/expression2/typename/IGCObject_DTypename.hpp
index 45781a2e..d002a847 100644
--- a/xo-expression2/include/xo/expression2/typename/IGCObject_DTypename.hpp
+++ b/xo-expression2/include/xo/expression2/typename/IGCObject_DTypename.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DTypename & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DTypename & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DTypename & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/include/xo/expression2/variable/IGCObject_DVariable.hpp b/xo-expression2/include/xo/expression2/variable/IGCObject_DVariable.hpp
index 9621d0f3..5fd34c21 100644
--- a/xo-expression2/include/xo/expression2/variable/IGCObject_DVariable.hpp
+++ b/xo-expression2/include/xo/expression2/variable/IGCObject_DVariable.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVariable & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVariable & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVariable & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-expression2/src/expression2/DApplyExpr.cpp b/xo-expression2/src/expression2/DApplyExpr.cpp
index 80f25139..9683d459 100644
--- a/xo-expression2/src/expression2/DApplyExpr.cpp
+++ b/xo-expression2/src/expression2/DApplyExpr.cpp
@@ -110,8 +110,11 @@ namespace xo {
         }
 
         DApplyExpr *
-        DApplyExpr::shallow_move(obj<AAllocator> mm) const noexcept {
-            DApplyExpr * copy = (DApplyExpr *)mm.alloc_copy((std::byte *)this);
+        DApplyExpr::shallow_move(obj<ACollector> gc) noexcept {
+            // note: not using ACollector.std_copy_for() here,
+            //       flexible array -> not move-constructible
+
+            DApplyExpr * copy = (DApplyExpr *)gc.alloc_copy_for(this);
 
             if (copy) {
                 copy->typeref_ = typeref_;
diff --git a/xo-expression2/src/expression2/DConstant.cpp b/xo-expression2/src/expression2/DConstant.cpp
index ea7a3d9f..420431bc 100644
--- a/xo-expression2/src/expression2/DConstant.cpp
+++ b/xo-expression2/src/expression2/DConstant.cpp
@@ -78,14 +78,9 @@ namespace xo {
         }
 
         DConstant *
-        DConstant::shallow_move(obj<AAllocator> mm) const noexcept
+        DConstant::shallow_move(obj<ACollector> gc) noexcept
         {
-            DConstant * copy = (DConstant *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-expression2/src/expression2/DDefineExpr.cpp b/xo-expression2/src/expression2/DDefineExpr.cpp
index 014da87c..e324b528 100644
--- a/xo-expression2/src/expression2/DDefineExpr.cpp
+++ b/xo-expression2/src/expression2/DDefineExpr.cpp
@@ -85,9 +85,9 @@ namespace xo {
         }
 
         DDefineExpr *
-        DDefineExpr::shallow_move(obj<AAllocator> mm) noexcept
+        DDefineExpr::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-expression2/src/expression2/DGlobalSymtab.cpp b/xo-expression2/src/expression2/DGlobalSymtab.cpp
index 2ea5b2ec..8d0f74cf 100644
--- a/xo-expression2/src/expression2/DGlobalSymtab.cpp
+++ b/xo-expression2/src/expression2/DGlobalSymtab.cpp
@@ -261,25 +261,9 @@ namespace xo {
         }
 
         DGlobalSymtab *
-        DGlobalSymtab::shallow_move(obj<AAllocator> mm) const noexcept
+        DGlobalSymtab::shallow_move(obj<ACollector> gc) noexcept
         {
-            /** can't use std_copy_for because of non-copyable dp<repr_type>
-             *
-             * TODO: rename to shallow_move() throughout, and have std_copy_for()
-             *       -> std_move_for()
-             *
-             **/
-
-            void * copy_mem = mm.alloc_copy_for(this);
-
-            if (copy_mem) {
-                DGlobalSymtab * self = const_cast<DGlobalSymtab*>(this);
-
-                return new (copy_mem) DGlobalSymtab(std::move(self->var_map_), vars_,
-                                                    std::move(self->type_map_), types_);
-            }
-
-            return nullptr;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-expression2/src/expression2/DIfElseExpr.cpp b/xo-expression2/src/expression2/DIfElseExpr.cpp
index 42d09fbb..3fb71682 100644
--- a/xo-expression2/src/expression2/DIfElseExpr.cpp
+++ b/xo-expression2/src/expression2/DIfElseExpr.cpp
@@ -89,14 +89,9 @@ namespace xo {
         }
 
         DIfElseExpr *
-        DIfElseExpr::shallow_move(obj<AAllocator> mm) const noexcept
+        DIfElseExpr::shallow_move(obj<ACollector> gc) noexcept
         {
-            DIfElseExpr * copy = (DIfElseExpr *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-expression2/src/expression2/DLambdaExpr.cpp b/xo-expression2/src/expression2/DLambdaExpr.cpp
index ebec0d40..4919840b 100644
--- a/xo-expression2/src/expression2/DLambdaExpr.cpp
+++ b/xo-expression2/src/expression2/DLambdaExpr.cpp
@@ -140,14 +140,8 @@ namespace xo {
         }
 
         DLambdaExpr *
-        DLambdaExpr::shallow_move(obj<AAllocator> mm) const noexcept {
-            DLambdaExpr * copy = (DLambdaExpr *)mm.alloc_copy((std::byte *)this);
-
-            if (copy) {
-                *copy = *this;
-            }
-
-            return copy;
+        DLambdaExpr::shallow_move(obj<ACollector> gc) noexcept {
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-expression2/src/expression2/DLocalSymtab.cpp b/xo-expression2/src/expression2/DLocalSymtab.cpp
index cf021038..d1c4930c 100644
--- a/xo-expression2/src/expression2/DLocalSymtab.cpp
+++ b/xo-expression2/src/expression2/DLocalSymtab.cpp
@@ -119,9 +119,9 @@ namespace xo {
         }
 
         DLocalSymtab *
-        DLocalSymtab::shallow_move(obj<AAllocator> mm) noexcept
+        DLocalSymtab::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-expression2/src/expression2/DSequenceExpr.cpp b/xo-expression2/src/expression2/DSequenceExpr.cpp
index 39dcc999..33149785 100644
--- a/xo-expression2/src/expression2/DSequenceExpr.cpp
+++ b/xo-expression2/src/expression2/DSequenceExpr.cpp
@@ -120,14 +120,9 @@ namespace xo {
         }
 
         DSequenceExpr *
-        DSequenceExpr::shallow_move(obj<AAllocator> mm) const noexcept
+        DSequenceExpr::shallow_move(obj<ACollector> gc) noexcept
         {
-            DSequenceExpr * copy = (DSequenceExpr *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-expression2/src/expression2/DTypename.cpp b/xo-expression2/src/expression2/DTypename.cpp
index e02b483e..81509949 100644
--- a/xo-expression2/src/expression2/DTypename.cpp
+++ b/xo-expression2/src/expression2/DTypename.cpp
@@ -47,9 +47,9 @@ namespace xo {
         }
 
         DTypename *
-        DTypename::shallow_move(obj<AAllocator> mm) noexcept
+        DTypename::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         size_t
diff --git a/xo-expression2/src/expression2/DVarRef.cpp b/xo-expression2/src/expression2/DVarRef.cpp
index e2866c23..186fa29a 100644
--- a/xo-expression2/src/expression2/DVarRef.cpp
+++ b/xo-expression2/src/expression2/DVarRef.cpp
@@ -65,14 +65,9 @@ namespace xo {
         }
 
         DVarRef *
-        DVarRef::shallow_move(obj<AAllocator> mm) const noexcept
+        DVarRef::shallow_move(obj<ACollector> gc) noexcept
         {
-            DVarRef * copy = (DVarRef *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-expression2/src/expression2/DVariable.cpp b/xo-expression2/src/expression2/DVariable.cpp
index 1b986c0b..f11000aa 100644
--- a/xo-expression2/src/expression2/DVariable.cpp
+++ b/xo-expression2/src/expression2/DVariable.cpp
@@ -45,15 +45,9 @@ namespace xo {
         }
 
         DVariable *
-        DVariable::shallow_move(obj<AAllocator> mm) const noexcept
+        DVariable::shallow_move(obj<ACollector> gc) noexcept
         {
-            DVariable * copy = (DVariable *)mm.alloc_copy((std::byte *)this);
-
-            if (copy) {
-                *copy = *this;
-            }
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         size_t
diff --git a/xo-expression2/src/expression2/IGCObject_DApplyExpr.cpp b/xo-expression2/src/expression2/IGCObject_DApplyExpr.cpp
index 28375cce..2a731c0b 100644
--- a/xo-expression2/src/expression2/IGCObject_DApplyExpr.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DApplyExpr.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DApplyExpr::shallow_move(DApplyExpr & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DApplyExpr::shallow_move(DApplyExpr & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DApplyExpr::forward_children(DApplyExpr & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DConstant.cpp b/xo-expression2/src/expression2/IGCObject_DConstant.cpp
index dff013b1..ae5a701f 100644
--- a/xo-expression2/src/expression2/IGCObject_DConstant.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DConstant.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DConstant::shallow_move(DConstant & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DConstant::shallow_move(DConstant & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DConstant::forward_children(DConstant & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DDefineExpr.cpp b/xo-expression2/src/expression2/IGCObject_DDefineExpr.cpp
index 5adf8fc6..1e2c3bb8 100644
--- a/xo-expression2/src/expression2/IGCObject_DDefineExpr.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DDefineExpr.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DDefineExpr::shallow_move(DDefineExpr & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DDefineExpr::shallow_move(DDefineExpr & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DDefineExpr::forward_children(DDefineExpr & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DGlobalSymtab.cpp b/xo-expression2/src/expression2/IGCObject_DGlobalSymtab.cpp
index 005e3ad3..3f596d01 100644
--- a/xo-expression2/src/expression2/IGCObject_DGlobalSymtab.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DGlobalSymtab.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DGlobalSymtab::shallow_move(DGlobalSymtab & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DGlobalSymtab::shallow_move(DGlobalSymtab & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DGlobalSymtab::forward_children(DGlobalSymtab & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DIfElseExpr.cpp b/xo-expression2/src/expression2/IGCObject_DIfElseExpr.cpp
index 9c28f2e0..240906f2 100644
--- a/xo-expression2/src/expression2/IGCObject_DIfElseExpr.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DIfElseExpr.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DIfElseExpr::shallow_move(DIfElseExpr & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DIfElseExpr::shallow_move(DIfElseExpr & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DIfElseExpr::forward_children(DIfElseExpr & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DLambdaExpr.cpp b/xo-expression2/src/expression2/IGCObject_DLambdaExpr.cpp
index bfe386a2..c0a95847 100644
--- a/xo-expression2/src/expression2/IGCObject_DLambdaExpr.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DLambdaExpr.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DLambdaExpr::shallow_move(DLambdaExpr & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DLambdaExpr::shallow_move(DLambdaExpr & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DLambdaExpr::forward_children(DLambdaExpr & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DLocalSymtab.cpp b/xo-expression2/src/expression2/IGCObject_DLocalSymtab.cpp
index 7078db9a..02941925 100644
--- a/xo-expression2/src/expression2/IGCObject_DLocalSymtab.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DLocalSymtab.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DLocalSymtab::shallow_move(DLocalSymtab & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DLocalSymtab::shallow_move(DLocalSymtab & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DLocalSymtab::forward_children(DLocalSymtab & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DSequenceExpr.cpp b/xo-expression2/src/expression2/IGCObject_DSequenceExpr.cpp
index 446a78bb..93af6f10 100644
--- a/xo-expression2/src/expression2/IGCObject_DSequenceExpr.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DSequenceExpr.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DSequenceExpr::shallow_move(DSequenceExpr & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DSequenceExpr::shallow_move(DSequenceExpr & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DSequenceExpr::forward_children(DSequenceExpr & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DTypename.cpp b/xo-expression2/src/expression2/IGCObject_DTypename.cpp
index 154a8b4a..58df5bff 100644
--- a/xo-expression2/src/expression2/IGCObject_DTypename.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DTypename.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DTypename::shallow_move(DTypename & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DTypename::shallow_move(DTypename & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DTypename::forward_children(DTypename & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/IGCObject_DVarRef.cpp b/xo-expression2/src/expression2/IGCObject_DVarRef.cpp
index b6b5e077..64967c9b 100644
--- a/xo-expression2/src/expression2/IGCObject_DVarRef.cpp
+++ b/xo-expression2/src/expression2/IGCObject_DVarRef.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVarRef::shallow_move(DVarRef & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVarRef::shallow_move(DVarRef & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVarRef::forward_children(DVarRef & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-expression2/src/expression2/facet/IGCObject_DVariable.cpp b/xo-expression2/src/expression2/facet/IGCObject_DVariable.cpp
index 8a49292b..d418145c 100644
--- a/xo-expression2/src/expression2/facet/IGCObject_DVariable.cpp
+++ b/xo-expression2/src/expression2/facet/IGCObject_DVariable.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVariable::shallow_move(DVariable & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVariable::shallow_move(DVariable & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVariable::forward_children(DVariable & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-gc/src/gc/GCObjectStore.cpp b/xo-gc/src/gc/GCObjectStore.cpp
index 621a1548..4076fd90 100644
--- a/xo-gc/src/gc/GCObjectStore.cpp
+++ b/xo-gc/src/gc/GCObjectStore.cpp
@@ -870,7 +870,7 @@ namespace xo {
 
             //obj<AAllocator, DX1Collector> gc_gco(gc);
 
-            void * to_dest = iface->shallow_move(from_src, gc->ref<AAllocator>());
+            void * to_dest = iface->shallow_move(from_src, gc->ref<ACollector>());
 
             log && log(xtag("from_src", from_src), xtag("to_dest", to_dest));
             log && log(xtag("tseq", info.tseq()),
diff --git a/xo-interpreter2/include/xo/interpreter2/DClosure.hpp b/xo-interpreter2/include/xo/interpreter2/DClosure.hpp
index aef74663..e57f6a1a 100644
--- a/xo-interpreter2/include/xo/interpreter2/DClosure.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/DClosure.hpp
@@ -58,7 +58,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DClosure * shallow_move(obj<AAllocator> mm) const noexcept;
+            DClosure * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/DLocalEnv.hpp b/xo-interpreter2/include/xo/interpreter2/DLocalEnv.hpp
index 76cac024..6ecd3eb6 100644
--- a/xo-interpreter2/include/xo/interpreter2/DLocalEnv.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/DLocalEnv.hpp
@@ -55,7 +55,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DLocalEnv * shallow_move(obj<AAllocator> mm) const noexcept;
+            DLocalEnv * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/DVsmApplyClosureFrame.hpp b/xo-interpreter2/include/xo/interpreter2/DVsmApplyClosureFrame.hpp
index 718c52b3..ae422cb1 100644
--- a/xo-interpreter2/include/xo/interpreter2/DVsmApplyClosureFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/DVsmApplyClosureFrame.hpp
@@ -40,7 +40,7 @@ namespace xo {
 
             /** gcobject facet **/
             std::size_t shallow_size() const noexcept;
-            DVsmApplyClosureFrame * shallow_move(obj<AAllocator> mm) const noexcept;
+            DVsmApplyClosureFrame * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             /** pretty-printing support **/
diff --git a/xo-interpreter2/include/xo/interpreter2/DVsmApplyFrame.hpp b/xo-interpreter2/include/xo/interpreter2/DVsmApplyFrame.hpp
index d761cd18..99093f37 100644
--- a/xo-interpreter2/include/xo/interpreter2/DVsmApplyFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/DVsmApplyFrame.hpp
@@ -38,7 +38,7 @@ namespace xo {
             void assign_fn(obj<AGCObject> x) { this->fn_ = x; }
 
             std::size_t shallow_size() const noexcept;
-            DVsmApplyFrame * shallow_move(obj<AAllocator> mm) const noexcept;
+            DVsmApplyFrame * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             /** pretty-printing support **/
diff --git a/xo-interpreter2/include/xo/interpreter2/DVsmDefContFrame.hpp b/xo-interpreter2/include/xo/interpreter2/DVsmDefContFrame.hpp
index d128d357..0ad31cca 100644
--- a/xo-interpreter2/include/xo/interpreter2/DVsmDefContFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/DVsmDefContFrame.hpp
@@ -51,7 +51,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DVsmDefContFrame * shallow_move(obj<AAllocator> mm) noexcept;
+            DVsmDefContFrame * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/DVsmEvalArgsFrame.hpp b/xo-interpreter2/include/xo/interpreter2/DVsmEvalArgsFrame.hpp
index c389f214..a1903e94 100644
--- a/xo-interpreter2/include/xo/interpreter2/DVsmEvalArgsFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/DVsmEvalArgsFrame.hpp
@@ -43,7 +43,7 @@ namespace xo {
             int32_t increment_arg() { return ++i_arg_; }
 
             std::size_t shallow_size() const noexcept;
-            DVsmEvalArgsFrame * shallow_move(obj<AAllocator> mm) const noexcept;
+            DVsmEvalArgsFrame * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             bool pretty(const ppindentinfo & ppii) const;
diff --git a/xo-interpreter2/include/xo/interpreter2/DVsmIfElseContFrame.hpp b/xo-interpreter2/include/xo/interpreter2/DVsmIfElseContFrame.hpp
index 09fcd076..3c438e51 100644
--- a/xo-interpreter2/include/xo/interpreter2/DVsmIfElseContFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/DVsmIfElseContFrame.hpp
@@ -51,7 +51,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DVsmIfElseContFrame * shallow_move(obj<AAllocator> mm) noexcept;
+            DVsmIfElseContFrame * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/DVsmSeqContFrame.hpp b/xo-interpreter2/include/xo/interpreter2/DVsmSeqContFrame.hpp
index 4692425b..959edfb0 100644
--- a/xo-interpreter2/include/xo/interpreter2/DVsmSeqContFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/DVsmSeqContFrame.hpp
@@ -56,7 +56,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DVsmSeqContFrame * shallow_move(obj<AAllocator> mm) noexcept;
+            DVsmSeqContFrame * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/define/IGCObject_DVsmDefContFrame.hpp b/xo-interpreter2/include/xo/interpreter2/define/IGCObject_DVsmDefContFrame.hpp
index f4a7c4d1..4cb21afa 100644
--- a/xo-interpreter2/include/xo/interpreter2/define/IGCObject_DVsmDefContFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/define/IGCObject_DVsmDefContFrame.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVsmDefContFrame & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVsmDefContFrame & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVsmDefContFrame & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DClosure.hpp b/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DClosure.hpp
index d5933283..86becbdf 100644
--- a/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DClosure.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DClosure.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DClosure & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DClosure & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DClosure & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmApplyClosureFrame.hpp b/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmApplyClosureFrame.hpp
index ab9e223a..01bef341 100644
--- a/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmApplyClosureFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmApplyClosureFrame.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVsmApplyClosureFrame & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVsmApplyClosureFrame & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVsmApplyClosureFrame & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmApplyFrame.hpp b/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmApplyFrame.hpp
index aa65d6e9..a3e0d31b 100644
--- a/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmApplyFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmApplyFrame.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVsmApplyFrame & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVsmApplyFrame & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVsmApplyFrame & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmEvalArgsFrame.hpp b/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmEvalArgsFrame.hpp
index 57d28ebe..42c26b03 100644
--- a/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmEvalArgsFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/detail/IGCObject_DVsmEvalArgsFrame.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVsmEvalArgsFrame & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVsmEvalArgsFrame & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVsmEvalArgsFrame & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/env/IGCObject_DLocalEnv.hpp b/xo-interpreter2/include/xo/interpreter2/env/IGCObject_DLocalEnv.hpp
index 7105768a..55064b27 100644
--- a/xo-interpreter2/include/xo/interpreter2/env/IGCObject_DLocalEnv.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/env/IGCObject_DLocalEnv.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DLocalEnv & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DLocalEnv & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DLocalEnv & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/ifelse/IGCObject_DVsmIfElseContFrame.hpp b/xo-interpreter2/include/xo/interpreter2/ifelse/IGCObject_DVsmIfElseContFrame.hpp
index 63e3ad2a..ab9a13c8 100644
--- a/xo-interpreter2/include/xo/interpreter2/ifelse/IGCObject_DVsmIfElseContFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/ifelse/IGCObject_DVsmIfElseContFrame.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVsmIfElseContFrame & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVsmIfElseContFrame & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVsmIfElseContFrame & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/sequence/IGCObject_DVsmSeqContFrame.hpp b/xo-interpreter2/include/xo/interpreter2/sequence/IGCObject_DVsmSeqContFrame.hpp
index a657a217..d654d8a1 100644
--- a/xo-interpreter2/include/xo/interpreter2/sequence/IGCObject_DVsmSeqContFrame.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/sequence/IGCObject_DVsmSeqContFrame.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVsmSeqContFrame & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVsmSeqContFrame & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVsmSeqContFrame & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/include/xo/interpreter2/vsm/DVirtualSchematikaMachine.hpp b/xo-interpreter2/include/xo/interpreter2/vsm/DVirtualSchematikaMachine.hpp
index ecaac469..fa9a6929 100644
--- a/xo-interpreter2/include/xo/interpreter2/vsm/DVirtualSchematikaMachine.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/vsm/DVirtualSchematikaMachine.hpp
@@ -153,7 +153,7 @@ namespace xo {
             /** shallow copy during gc cycle.  Not implemented!  Only intending to support
              *  VSM as virtual root
              **/
-            DVirtualSchematikaMachine * shallow_move(obj<AAllocator> mm) const noexcept;
+            DVirtualSchematikaMachine * shallow_move(obj<ACollector> gc) noexcept;
 
             /** forward gc-aware child pointers
              **/
diff --git a/xo-interpreter2/include/xo/interpreter2/vsm/IGCObject_DVirtualSchematikaMachine.hpp b/xo-interpreter2/include/xo/interpreter2/vsm/IGCObject_DVirtualSchematikaMachine.hpp
index 6f7c0eb8..71786a28 100644
--- a/xo-interpreter2/include/xo/interpreter2/vsm/IGCObject_DVirtualSchematikaMachine.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/vsm/IGCObject_DVirtualSchematikaMachine.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DVirtualSchematikaMachine & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DVirtualSchematikaMachine & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DVirtualSchematikaMachine & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-interpreter2/src/interpreter2/DClosure.cpp b/xo-interpreter2/src/interpreter2/DClosure.cpp
index ed95334f..ca8f3bee 100644
--- a/xo-interpreter2/src/interpreter2/DClosure.cpp
+++ b/xo-interpreter2/src/interpreter2/DClosure.cpp
@@ -70,13 +70,8 @@ namespace xo {
         }
 
         DClosure *
-        DClosure::shallow_move(obj<AAllocator> mm) const noexcept {
-            DClosure * copy = (DClosure *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+        DClosure::shallow_move(obj<ACollector> gc) noexcept {
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-interpreter2/src/interpreter2/DLocalEnv.cpp b/xo-interpreter2/src/interpreter2/DLocalEnv.cpp
index 94f27422..a12200a0 100644
--- a/xo-interpreter2/src/interpreter2/DLocalEnv.cpp
+++ b/xo-interpreter2/src/interpreter2/DLocalEnv.cpp
@@ -97,13 +97,8 @@ namespace xo {
         }
 
         DLocalEnv *
-        DLocalEnv::shallow_move(obj<AAllocator> mm) const noexcept {
-            DLocalEnv * copy = (DLocalEnv *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+        DLocalEnv::shallow_move(obj<ACollector> gc) noexcept {
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-interpreter2/src/interpreter2/DVirtualSchematikaMachine.cpp b/xo-interpreter2/src/interpreter2/DVirtualSchematikaMachine.cpp
index a196363e..5ccb333c 100644
--- a/xo-interpreter2/src/interpreter2/DVirtualSchematikaMachine.cpp
+++ b/xo-interpreter2/src/interpreter2/DVirtualSchematikaMachine.cpp
@@ -954,11 +954,14 @@ namespace xo {
         }
 
         DVirtualSchematikaMachine *
-        DVirtualSchematikaMachine::shallow_move(obj<AAllocator> mm) const noexcept
+        DVirtualSchematikaMachine::shallow_move(obj<ACollector> gc) noexcept
         {
-            (void)mm;
+            (void)gc;
 
-            /** not copyable (because SchematikaReader isn't) **/
+            /** TODO: should be able to use gc.std_copy_for(this) now
+             *  that shallow_move uses move construction.
+             *  DVirtualSchematikaMachine is (or can be made) moveable.
+             **/
 
             assert(false);
 
diff --git a/xo-interpreter2/src/interpreter2/DVsmApplyClosureFrame.cpp b/xo-interpreter2/src/interpreter2/DVsmApplyClosureFrame.cpp
index d2cfdb35..c7dca412 100644
--- a/xo-interpreter2/src/interpreter2/DVsmApplyClosureFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/DVsmApplyClosureFrame.cpp
@@ -39,15 +39,9 @@ namespace xo {
         }
 
         DVsmApplyClosureFrame *
-        DVsmApplyClosureFrame::shallow_move(obj<AAllocator> mm) const noexcept
+        DVsmApplyClosureFrame::shallow_move(obj<ACollector> gc) noexcept
         {
-            DVsmApplyClosureFrame * copy
-                = (DVsmApplyClosureFrame *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-interpreter2/src/interpreter2/DVsmApplyFrame.cpp b/xo-interpreter2/src/interpreter2/DVsmApplyFrame.cpp
index 9a50c117..f51742f7 100644
--- a/xo-interpreter2/src/interpreter2/DVsmApplyFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/DVsmApplyFrame.cpp
@@ -47,14 +47,9 @@ namespace xo {
         }
 
         DVsmApplyFrame *
-        DVsmApplyFrame::shallow_move(obj<AAllocator> mm) const noexcept
+        DVsmApplyFrame::shallow_move(obj<ACollector> gc) noexcept
         {
-            DVsmApplyFrame * copy = (DVsmApplyFrame *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-interpreter2/src/interpreter2/DVsmDefContFrame.cpp b/xo-interpreter2/src/interpreter2/DVsmDefContFrame.cpp
index d1f3e2b2..f3a8b35b 100644
--- a/xo-interpreter2/src/interpreter2/DVsmDefContFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/DVsmDefContFrame.cpp
@@ -38,9 +38,9 @@ namespace xo {
         }
 
         DVsmDefContFrame *
-        DVsmDefContFrame::shallow_move(obj<AAllocator> mm) noexcept
+        DVsmDefContFrame::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for<DVsmDefContFrame>(this);
+            return gc.std_copy_for<DVsmDefContFrame>(this);
         }
 
         std::size_t
diff --git a/xo-interpreter2/src/interpreter2/DVsmEvalArgsFrame.cpp b/xo-interpreter2/src/interpreter2/DVsmEvalArgsFrame.cpp
index 0ff4ceb2..c487ae59 100644
--- a/xo-interpreter2/src/interpreter2/DVsmEvalArgsFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/DVsmEvalArgsFrame.cpp
@@ -48,15 +48,9 @@ namespace xo {
         }
 
         DVsmEvalArgsFrame *
-        DVsmEvalArgsFrame::shallow_move(obj<AAllocator> mm) const noexcept
+        DVsmEvalArgsFrame::shallow_move(obj<ACollector> gc) noexcept
         {
-            DVsmEvalArgsFrame * copy
-                = (DVsmEvalArgsFrame *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-interpreter2/src/interpreter2/DVsmIfElseContFrame.cpp b/xo-interpreter2/src/interpreter2/DVsmIfElseContFrame.cpp
index 075f7bd3..4978ff9c 100644
--- a/xo-interpreter2/src/interpreter2/DVsmIfElseContFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/DVsmIfElseContFrame.cpp
@@ -36,9 +36,9 @@ namespace xo {
         }
 
         DVsmIfElseContFrame *
-        DVsmIfElseContFrame::shallow_move(obj<AAllocator> mm) noexcept
+        DVsmIfElseContFrame::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for<DVsmIfElseContFrame>(this);
+            return gc.std_copy_for<DVsmIfElseContFrame>(this);
         }
 
         std::size_t
diff --git a/xo-interpreter2/src/interpreter2/DVsmSeqContFrame.cpp b/xo-interpreter2/src/interpreter2/DVsmSeqContFrame.cpp
index d6160e8d..7ffea82e 100644
--- a/xo-interpreter2/src/interpreter2/DVsmSeqContFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/DVsmSeqContFrame.cpp
@@ -39,9 +39,9 @@ namespace xo {
         }
 
         DVsmSeqContFrame *
-        DVsmSeqContFrame::shallow_move(obj<AAllocator> mm) noexcept
+        DVsmSeqContFrame::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for<DVsmSeqContFrame>(this);
+            return gc.std_copy_for<DVsmSeqContFrame>(this);
         }
 
         std::size_t
diff --git a/xo-interpreter2/src/interpreter2/IGCObject_DClosure.cpp b/xo-interpreter2/src/interpreter2/IGCObject_DClosure.cpp
index 33544907..99e834b8 100644
--- a/xo-interpreter2/src/interpreter2/IGCObject_DClosure.cpp
+++ b/xo-interpreter2/src/interpreter2/IGCObject_DClosure.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DClosure::shallow_move(DClosure & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DClosure::shallow_move(DClosure & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DClosure::forward_children(DClosure & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-interpreter2/src/interpreter2/IGCObject_DVsmApplyClosureFrame.cpp b/xo-interpreter2/src/interpreter2/IGCObject_DVsmApplyClosureFrame.cpp
index 3aa994fd..a96ad2d7 100644
--- a/xo-interpreter2/src/interpreter2/IGCObject_DVsmApplyClosureFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/IGCObject_DVsmApplyClosureFrame.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVsmApplyClosureFrame::shallow_move(DVsmApplyClosureFrame & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVsmApplyClosureFrame::shallow_move(DVsmApplyClosureFrame & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVsmApplyClosureFrame::forward_children(DVsmApplyClosureFrame & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-interpreter2/src/interpreter2/IGCObject_DVsmApplyFrame.cpp b/xo-interpreter2/src/interpreter2/IGCObject_DVsmApplyFrame.cpp
index a1da32b8..9666fdec 100644
--- a/xo-interpreter2/src/interpreter2/IGCObject_DVsmApplyFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/IGCObject_DVsmApplyFrame.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVsmApplyFrame::shallow_move(DVsmApplyFrame & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVsmApplyFrame::shallow_move(DVsmApplyFrame & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVsmApplyFrame::forward_children(DVsmApplyFrame & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-interpreter2/src/interpreter2/IGCObject_DVsmDefContFrame.cpp b/xo-interpreter2/src/interpreter2/IGCObject_DVsmDefContFrame.cpp
index 02abd4cb..2acd7b24 100644
--- a/xo-interpreter2/src/interpreter2/IGCObject_DVsmDefContFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/IGCObject_DVsmDefContFrame.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVsmDefContFrame::shallow_move(DVsmDefContFrame & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVsmDefContFrame::shallow_move(DVsmDefContFrame & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVsmDefContFrame::forward_children(DVsmDefContFrame & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-interpreter2/src/interpreter2/IGCObject_DVsmEvalArgsFrame.cpp b/xo-interpreter2/src/interpreter2/IGCObject_DVsmEvalArgsFrame.cpp
index 8f33ece1..d1d6a0b6 100644
--- a/xo-interpreter2/src/interpreter2/IGCObject_DVsmEvalArgsFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/IGCObject_DVsmEvalArgsFrame.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVsmEvalArgsFrame::shallow_move(DVsmEvalArgsFrame & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVsmEvalArgsFrame::shallow_move(DVsmEvalArgsFrame & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVsmEvalArgsFrame::forward_children(DVsmEvalArgsFrame & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-interpreter2/src/interpreter2/IGCObject_DVsmIfElseContFrame.cpp b/xo-interpreter2/src/interpreter2/IGCObject_DVsmIfElseContFrame.cpp
index 939d7ce4..38f4881d 100644
--- a/xo-interpreter2/src/interpreter2/IGCObject_DVsmIfElseContFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/IGCObject_DVsmIfElseContFrame.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVsmIfElseContFrame::shallow_move(DVsmIfElseContFrame & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVsmIfElseContFrame::shallow_move(DVsmIfElseContFrame & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVsmIfElseContFrame::forward_children(DVsmIfElseContFrame & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-interpreter2/src/interpreter2/IGCObject_DVsmSeqContFrame.cpp b/xo-interpreter2/src/interpreter2/IGCObject_DVsmSeqContFrame.cpp
index 5d52ae74..3d57aaa1 100644
--- a/xo-interpreter2/src/interpreter2/IGCObject_DVsmSeqContFrame.cpp
+++ b/xo-interpreter2/src/interpreter2/IGCObject_DVsmSeqContFrame.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVsmSeqContFrame::shallow_move(DVsmSeqContFrame & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVsmSeqContFrame::shallow_move(DVsmSeqContFrame & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVsmSeqContFrame::forward_children(DVsmSeqContFrame & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-interpreter2/src/interpreter2/facet/IGCObject_DLocalEnv.cpp b/xo-interpreter2/src/interpreter2/facet/IGCObject_DLocalEnv.cpp
index 61e645f6..ed9f18fd 100644
--- a/xo-interpreter2/src/interpreter2/facet/IGCObject_DLocalEnv.cpp
+++ b/xo-interpreter2/src/interpreter2/facet/IGCObject_DLocalEnv.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DLocalEnv::shallow_move(DLocalEnv & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DLocalEnv::shallow_move(DLocalEnv & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DLocalEnv::forward_children(DLocalEnv & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-interpreter2/src/interpreter2/facet/IGCObject_DVirtualSchematikaMachine.cpp b/xo-interpreter2/src/interpreter2/facet/IGCObject_DVirtualSchematikaMachine.cpp
index 354478ad..ddf77335 100644
--- a/xo-interpreter2/src/interpreter2/facet/IGCObject_DVirtualSchematikaMachine.cpp
+++ b/xo-interpreter2/src/interpreter2/facet/IGCObject_DVirtualSchematikaMachine.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DVirtualSchematikaMachine::shallow_move(DVirtualSchematikaMachine & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DVirtualSchematikaMachine::shallow_move(DVirtualSchematikaMachine & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DVirtualSchematikaMachine::forward_children(DVirtualSchematikaMachine & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-numeric/include/xo/numeric/detail/ANumeric.hpp b/xo-numeric/include/xo/numeric/detail/ANumeric.hpp
index bda27456..7c8e0c99 100644
--- a/xo-numeric/include/xo/numeric/detail/ANumeric.hpp
+++ b/xo-numeric/include/xo/numeric/detail/ANumeric.hpp
@@ -42,6 +42,11 @@ public:
     /** @defgroup scm-numeric-methods **/
     ///@{
     // const methods
+    /** An uninitialized ANumeric instance will have zero vtable pointer (per {linux,osx} abi).
+     *  Use case for this is narrow. We go to some lengths to avoid null vtable pointers. For example
+     *  obj<AFacet> will have non-null vtable (via IFacet_Any) with all methods terminating.
+     **/
+    bool _has_null_vptr() const noexcept { return *reinterpret_cast<const void * const *>(this) == nullptr; }
     /** RTTI: unique id# for actual runtime data representation **/
     virtual typeseq _typeseq() const noexcept = 0;
     /** destroy instance @p d; calls c++ dtor only for actual runtime type; does not recover memory **/
diff --git a/xo-numeric/include/xo/numeric/detail/RNumeric.hpp b/xo-numeric/include/xo/numeric/detail/RNumeric.hpp
index 86cac666..35a704ec 100644
--- a/xo-numeric/include/xo/numeric/detail/RNumeric.hpp
+++ b/xo-numeric/include/xo/numeric/detail/RNumeric.hpp
@@ -46,6 +46,7 @@ public:
     ///@{
 
     // explicit injected content
+    static obj<ANumeric> multiply(obj<ANumeric> lhs, obj<ANumeric> rhs);
 
     // builtin methods
     typeseq _typeseq() const noexcept { return O::iface()->_typeseq(); }
diff --git a/xo-object2/include/xo/object2/DArray.hpp b/xo-object2/include/xo/object2/DArray.hpp
index 99d1b3d7..a455046d 100644
--- a/xo-object2/include/xo/object2/DArray.hpp
+++ b/xo-object2/include/xo/object2/DArray.hpp
@@ -148,7 +148,7 @@ namespace xo {
             /** shallow memory consumption. Excludes child objects **/
             AAllocator::size_type shallow_size() const noexcept;
             /** return shallow copy of this array, using memory from @p mm **/
-            DArray * shallow_move(obj<AAllocator> mm) const noexcept;
+            DArray * shallow_move(obj<ACollector> gc) noexcept;
             /** forward elements to @p gc to-space; replace originals with forarding pointers **/
             AAllocator::size_type forward_children(obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/include/xo/object2/DBoolean.hpp b/xo-object2/include/xo/object2/DBoolean.hpp
index 34ffda16..31bf41b7 100644
--- a/xo-object2/include/xo/object2/DBoolean.hpp
+++ b/xo-object2/include/xo/object2/DBoolean.hpp
@@ -38,7 +38,7 @@ namespace xo {
             // GCObject facet
 
             std::size_t shallow_size() const noexcept;
-            DBoolean * shallow_move(obj<AAllocator> mm) const noexcept;
+            DBoolean * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
         private:
diff --git a/xo-object2/include/xo/object2/DDictionary.hpp b/xo-object2/include/xo/object2/DDictionary.hpp
index 5e6ecaec..219e7838 100644
--- a/xo-object2/include/xo/object2/DDictionary.hpp
+++ b/xo-object2/include/xo/object2/DDictionary.hpp
@@ -203,7 +203,7 @@ namespace xo {
             /** shallow memory consumption. Excludes child objects **/
             AAllocator::size_type shallow_size() const noexcept;
             /** return shallow copy of this array, using memory from @p mm **/
-            DDictionary * shallow_move(obj<AAllocator> mm) noexcept;
+            DDictionary * shallow_move(obj<ACollector> gc) noexcept;
             /** forward elements to @p gc to-space; replace originals with forarding pointers **/
             AAllocator::size_type forward_children(obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/include/xo/object2/DFloat.hpp b/xo-object2/include/xo/object2/DFloat.hpp
index b7d56e9c..949883ab 100644
--- a/xo-object2/include/xo/object2/DFloat.hpp
+++ b/xo-object2/include/xo/object2/DFloat.hpp
@@ -35,7 +35,7 @@ namespace xo {
 
             // GCObject facet
             std::size_t shallow_size() const noexcept;
-            DFloat * shallow_move(obj<AAllocator> mm) const noexcept;
+            DFloat * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
         private:
diff --git a/xo-object2/include/xo/object2/DInteger.hpp b/xo-object2/include/xo/object2/DInteger.hpp
index 6a6194bf..d3969b75 100644
--- a/xo-object2/include/xo/object2/DInteger.hpp
+++ b/xo-object2/include/xo/object2/DInteger.hpp
@@ -40,7 +40,7 @@ namespace xo {
             // GCObject facet
 
             std::size_t shallow_size() const noexcept;
-            DInteger * shallow_move(obj<AAllocator> mm) const noexcept;
+            DInteger * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
         private:
diff --git a/xo-object2/include/xo/object2/DList.hpp b/xo-object2/include/xo/object2/DList.hpp
index 8fff47d5..199ec6e5 100644
--- a/xo-object2/include/xo/object2/DList.hpp
+++ b/xo-object2/include/xo/object2/DList.hpp
@@ -70,7 +70,7 @@ namespace xo {
             /** @defgroup xo-scm-list-gcobject-facet gcobject facet **/
             ///@{
             size_type shallow_size() const noexcept;
-            DList * shallow_move(obj<AAllocator> mm) noexcept;
+            DList * shallow_move(obj<ACollector> gc) noexcept;
             size_type forward_children(obj<ACollector> gc) noexcept;
             ///@}
 
diff --git a/xo-object2/include/xo/object2/DRuntimeError.hpp b/xo-object2/include/xo/object2/DRuntimeError.hpp
index 957c8481..2ee93061 100644
--- a/xo-object2/include/xo/object2/DRuntimeError.hpp
+++ b/xo-object2/include/xo/object2/DRuntimeError.hpp
@@ -50,7 +50,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DRuntimeError * shallow_move(obj<AAllocator> mm) const noexcept;
+            DRuntimeError * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-object2/include/xo/object2/array/IGCObject_DArray.hpp b/xo-object2/include/xo/object2/array/IGCObject_DArray.hpp
index ab8a85f1..58c202d7 100644
--- a/xo-object2/include/xo/object2/array/IGCObject_DArray.hpp
+++ b/xo-object2/include/xo/object2/array/IGCObject_DArray.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DArray & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DArray & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DArray & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/include/xo/object2/boolean/IGCObject_DBoolean.hpp b/xo-object2/include/xo/object2/boolean/IGCObject_DBoolean.hpp
index 5bc6e0c0..3ca03921 100644
--- a/xo-object2/include/xo/object2/boolean/IGCObject_DBoolean.hpp
+++ b/xo-object2/include/xo/object2/boolean/IGCObject_DBoolean.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DBoolean & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DBoolean & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DBoolean & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/include/xo/object2/dictionary/IGCObject_DDictionary.hpp b/xo-object2/include/xo/object2/dictionary/IGCObject_DDictionary.hpp
index 16fef8cb..b6da10c0 100644
--- a/xo-object2/include/xo/object2/dictionary/IGCObject_DDictionary.hpp
+++ b/xo-object2/include/xo/object2/dictionary/IGCObject_DDictionary.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DDictionary & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DDictionary & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DDictionary & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/include/xo/object2/error/IGCObject_DRuntimeError.hpp b/xo-object2/include/xo/object2/error/IGCObject_DRuntimeError.hpp
index 62cc6109..42e273ec 100644
--- a/xo-object2/include/xo/object2/error/IGCObject_DRuntimeError.hpp
+++ b/xo-object2/include/xo/object2/error/IGCObject_DRuntimeError.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DRuntimeError & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DRuntimeError & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DRuntimeError & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/include/xo/object2/list/IGCObject_DList.hpp b/xo-object2/include/xo/object2/list/IGCObject_DList.hpp
index 780ebda5..7218556a 100644
--- a/xo-object2/include/xo/object2/list/IGCObject_DList.hpp
+++ b/xo-object2/include/xo/object2/list/IGCObject_DList.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DList & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DList & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DList & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/include/xo/object2/number/IGCObject_DFloat.hpp b/xo-object2/include/xo/object2/number/IGCObject_DFloat.hpp
index b25e4626..88d4d563 100644
--- a/xo-object2/include/xo/object2/number/IGCObject_DFloat.hpp
+++ b/xo-object2/include/xo/object2/number/IGCObject_DFloat.hpp
@@ -54,7 +54,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DFloat & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DFloat & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DFloat & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/include/xo/object2/number/IGCObject_DInteger.hpp b/xo-object2/include/xo/object2/number/IGCObject_DInteger.hpp
index a87f253a..822ec168 100644
--- a/xo-object2/include/xo/object2/number/IGCObject_DInteger.hpp
+++ b/xo-object2/include/xo/object2/number/IGCObject_DInteger.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DInteger & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DInteger & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DInteger & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-object2/src/object2/DArray.cpp b/xo-object2/src/object2/DArray.cpp
index 2ae4ddc6..a70213f1 100644
--- a/xo-object2/src/object2/DArray.cpp
+++ b/xo-object2/src/object2/DArray.cpp
@@ -181,9 +181,12 @@ namespace xo {
         }
 
         DArray *
-        DArray::shallow_move(obj<AAllocator> mm) const noexcept
+        DArray::shallow_move(obj<ACollector> gc) noexcept
         {
-            DArray * copy = (DArray *)mm.alloc_copy((std::byte *)this);
+            // note: not using gc.std_copy_for() here.
+            //       flexible array -> compiler doesn't know actual DArray allocation size
+
+            DArray * copy = (DArray *)gc.alloc_copy((std::byte *)this);
 
             if (copy) {
                 copy->capacity_ = capacity_;
diff --git a/xo-object2/src/object2/DBoolean.cpp b/xo-object2/src/object2/DBoolean.cpp
index cb25f9e0..a8d5e85f 100644
--- a/xo-object2/src/object2/DBoolean.cpp
+++ b/xo-object2/src/object2/DBoolean.cpp
@@ -36,14 +36,9 @@ namespace xo {
         }
 
         DBoolean *
-        DBoolean::shallow_move(obj<AAllocator> mm) const noexcept
+        DBoolean::shallow_move(obj<ACollector> gc) noexcept
         {
-            DBoolean * copy = (DBoolean *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         size_t
diff --git a/xo-object2/src/object2/DDictionary.cpp b/xo-object2/src/object2/DDictionary.cpp
index 739fcedc..2f25f1b7 100644
--- a/xo-object2/src/object2/DDictionary.cpp
+++ b/xo-object2/src/object2/DDictionary.cpp
@@ -274,9 +274,9 @@ namespace xo {
         }
 
         DDictionary *
-        DDictionary::shallow_move(obj<AAllocator> mm) noexcept
+        DDictionary::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-object2/src/object2/DFloat.cpp b/xo-object2/src/object2/DFloat.cpp
index f7f8ff3e..4a9041c0 100644
--- a/xo-object2/src/object2/DFloat.cpp
+++ b/xo-object2/src/object2/DFloat.cpp
@@ -34,14 +34,9 @@ namespace xo {
         }
 
         DFloat *
-        DFloat::shallow_move(obj<AAllocator> mm) const noexcept
+        DFloat::shallow_move(obj<ACollector> gc) noexcept
         {
-            DFloat * copy = (DFloat *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         size_t
diff --git a/xo-object2/src/object2/DInteger.cpp b/xo-object2/src/object2/DInteger.cpp
index 7cbcedf0..600f48ec 100644
--- a/xo-object2/src/object2/DInteger.cpp
+++ b/xo-object2/src/object2/DInteger.cpp
@@ -34,14 +34,9 @@ namespace xo {
         }
 
         DInteger *
-        DInteger::shallow_move(obj<AAllocator> mm) const noexcept
+        DInteger::shallow_move(obj<ACollector> gc) noexcept
         {
-            DInteger * copy = (DInteger *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         size_t
diff --git a/xo-object2/src/object2/DList.cpp b/xo-object2/src/object2/DList.cpp
index be869073..f17a53f4 100644
--- a/xo-object2/src/object2/DList.cpp
+++ b/xo-object2/src/object2/DList.cpp
@@ -185,9 +185,9 @@ namespace xo {
         }
 
         DList *
-        DList::shallow_move(obj<AAllocator> mm) noexcept
+        DList::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         auto
diff --git a/xo-object2/src/object2/DRuntimeError.cpp b/xo-object2/src/object2/DRuntimeError.cpp
index 1f34596b..a52e1df9 100644
--- a/xo-object2/src/object2/DRuntimeError.cpp
+++ b/xo-object2/src/object2/DRuntimeError.cpp
@@ -59,14 +59,9 @@ namespace xo {
         }
 
         DRuntimeError *
-        DRuntimeError::shallow_move(obj<AAllocator> mm) const noexcept
+        DRuntimeError::shallow_move(obj<ACollector> gc) noexcept
         {
-            DRuntimeError * copy = (DRuntimeError *)mm.alloc_copy((std::byte *)this);
-
-            if (copy)
-                *copy = *this;
-
-            return copy;
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-object2/src/object2/IGCObject_DArray.cpp b/xo-object2/src/object2/IGCObject_DArray.cpp
index 7cde63e1..e4fa31c7 100644
--- a/xo-object2/src/object2/IGCObject_DArray.cpp
+++ b/xo-object2/src/object2/IGCObject_DArray.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DArray::shallow_move(DArray & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DArray::shallow_move(DArray & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DArray::forward_children(DArray & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-object2/src/object2/IGCObject_DBoolean.cpp b/xo-object2/src/object2/IGCObject_DBoolean.cpp
index ef503af9..2aed50e3 100644
--- a/xo-object2/src/object2/IGCObject_DBoolean.cpp
+++ b/xo-object2/src/object2/IGCObject_DBoolean.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DBoolean::shallow_move(DBoolean & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DBoolean::shallow_move(DBoolean & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DBoolean::forward_children(DBoolean & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-object2/src/object2/IGCObject_DDictionary.cpp b/xo-object2/src/object2/IGCObject_DDictionary.cpp
index 9d4bae65..e8f291aa 100644
--- a/xo-object2/src/object2/IGCObject_DDictionary.cpp
+++ b/xo-object2/src/object2/IGCObject_DDictionary.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DDictionary::shallow_move(DDictionary & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DDictionary::shallow_move(DDictionary & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DDictionary::forward_children(DDictionary & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-object2/src/object2/IGCObject_DFloat.cpp b/xo-object2/src/object2/IGCObject_DFloat.cpp
index a22a1b2f..7625cacb 100644
--- a/xo-object2/src/object2/IGCObject_DFloat.cpp
+++ b/xo-object2/src/object2/IGCObject_DFloat.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DFloat::shallow_move(DFloat & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DFloat::shallow_move(DFloat & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DFloat::forward_children(DFloat & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-object2/src/object2/IGCObject_DInteger.cpp b/xo-object2/src/object2/IGCObject_DInteger.cpp
index 4f74e5fe..9bb9bbf3 100644
--- a/xo-object2/src/object2/IGCObject_DInteger.cpp
+++ b/xo-object2/src/object2/IGCObject_DInteger.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DInteger::shallow_move(DInteger & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DInteger::shallow_move(DInteger & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DInteger::forward_children(DInteger & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-object2/src/object2/IGCObject_DList.cpp b/xo-object2/src/object2/IGCObject_DList.cpp
index 2512cc32..cbe8b71e 100644
--- a/xo-object2/src/object2/IGCObject_DList.cpp
+++ b/xo-object2/src/object2/IGCObject_DList.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DList::shallow_move(DList & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DList::shallow_move(DList & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DList::forward_children(DList & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-object2/src/object2/IGCObject_DRuntimeError.cpp b/xo-object2/src/object2/IGCObject_DRuntimeError.cpp
index cc755821..6917af76 100644
--- a/xo-object2/src/object2/IGCObject_DRuntimeError.cpp
+++ b/xo-object2/src/object2/IGCObject_DRuntimeError.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DRuntimeError::shallow_move(DRuntimeError & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DRuntimeError::shallow_move(DRuntimeError & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DRuntimeError::forward_children(DRuntimeError & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-procedure2/include/xo/procedure2/DPrimitive.hpp b/xo-procedure2/include/xo/procedure2/DPrimitive.hpp
index f602ebb6..d55e01ee 100644
--- a/xo-procedure2/include/xo/procedure2/DPrimitive.hpp
+++ b/xo-procedure2/include/xo/procedure2/DPrimitive.hpp
@@ -134,7 +134,7 @@ namespace xo {
             /** @defgroup scm-primitive-gcobject-facet **/
             ///@{
             std::size_t shallow_size() const noexcept;
-            Primitive * shallow_move(obj<AAllocator> mm) const noexcept;
+            Primitive * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
             ///@}
 
@@ -198,14 +198,8 @@ namespace xo {
 
         template <typename Fn>
         Primitive<Fn> *
-        Primitive<Fn>::shallow_move(obj<AAllocator> mm) const noexcept {
-            void * mem = mm.alloc_copy((std::byte *)this);
-
-            if (mem) {
-                return new (mem) Primitive(*this);
-            }
-
-            return nullptr;
+        Primitive<Fn>::shallow_move(obj<ACollector> gc) noexcept {
+            return gc.std_copy_for(this);
         }
 
         template <typename Fn>
diff --git a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_0.hpp b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_0.hpp
index cecc298c..53c073a4 100644
--- a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_0.hpp
+++ b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_0.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DPrimitive_gco_0 & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DPrimitive_gco_0 & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DPrimitive_gco_0 & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_1_gco.hpp b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_1_gco.hpp
index ac5c4f51..e2dd6381 100644
--- a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_1_gco.hpp
+++ b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_1_gco.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DPrimitive_gco_1_gco & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DPrimitive_gco_1_gco & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DPrimitive_gco_1_gco & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_2_dict_string.hpp b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_2_dict_string.hpp
index 772aabb3..c21ab140 100644
--- a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_2_dict_string.hpp
+++ b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_2_dict_string.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DPrimitive_gco_2_dict_string & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DPrimitive_gco_2_dict_string & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DPrimitive_gco_2_dict_string & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_2_gco_gco.hpp b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_2_gco_gco.hpp
index 266d1f42..b35e1004 100644
--- a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_2_gco_gco.hpp
+++ b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_2_gco_gco.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DPrimitive_gco_2_gco_gco & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DPrimitive_gco_2_gco_gco & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DPrimitive_gco_2_gco_gco & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_3_dict_string_gco.hpp b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_3_dict_string_gco.hpp
index 7abc1367..d0e23e33 100644
--- a/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_3_dict_string_gco.hpp
+++ b/xo-procedure2/include/xo/procedure2/detail/IGCObject_DPrimitive_gco_3_dict_string_gco.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DPrimitive_gco_3_dict_string_gco & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DPrimitive_gco_3_dict_string_gco & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DPrimitive_gco_3_dict_string_gco & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_0.cpp b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_0.cpp
index 948d1d60..2e0198f5 100644
--- a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_0.cpp
+++ b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_0.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DPrimitive_gco_0::shallow_move(DPrimitive_gco_0 & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DPrimitive_gco_0::shallow_move(DPrimitive_gco_0 & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DPrimitive_gco_0::forward_children(DPrimitive_gco_0 & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_1_gco.cpp b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_1_gco.cpp
index b5c1754b..2612c887 100644
--- a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_1_gco.cpp
+++ b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_1_gco.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DPrimitive_gco_1_gco::shallow_move(DPrimitive_gco_1_gco & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DPrimitive_gco_1_gco::shallow_move(DPrimitive_gco_1_gco & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DPrimitive_gco_1_gco::forward_children(DPrimitive_gco_1_gco & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_2_dict_string.cpp b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_2_dict_string.cpp
index 7c58550a..6173f6ca 100644
--- a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_2_dict_string.cpp
+++ b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_2_dict_string.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DPrimitive_gco_2_dict_string::shallow_move(DPrimitive_gco_2_dict_string & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DPrimitive_gco_2_dict_string::shallow_move(DPrimitive_gco_2_dict_string & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DPrimitive_gco_2_dict_string::forward_children(DPrimitive_gco_2_dict_string & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_2_gco_gco.cpp b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_2_gco_gco.cpp
index 347295b3..ab7cc1be 100644
--- a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_2_gco_gco.cpp
+++ b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_2_gco_gco.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DPrimitive_gco_2_gco_gco::shallow_move(DPrimitive_gco_2_gco_gco & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DPrimitive_gco_2_gco_gco::shallow_move(DPrimitive_gco_2_gco_gco & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DPrimitive_gco_2_gco_gco::forward_children(DPrimitive_gco_2_gco_gco & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_3_dict_string_gco.cpp b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_3_dict_string_gco.cpp
index 26a9f3fd..4134581c 100644
--- a/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_3_dict_string_gco.cpp
+++ b/xo-procedure2/src/procedure2/facet/IGCObject_DPrimitive_gco_3_dict_string_gco.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DPrimitive_gco_3_dict_string_gco::shallow_move(DPrimitive_gco_3_dict_string_gco & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DPrimitive_gco_3_dict_string_gco::shallow_move(DPrimitive_gco_3_dict_string_gco & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DPrimitive_gco_3_dict_string_gco::forward_children(DPrimitive_gco_3_dict_string_gco & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-reader2/include/xo/reader2/DGlobalEnv.hpp b/xo-reader2/include/xo/reader2/DGlobalEnv.hpp
index 0c1536ee..96cd5771 100644
--- a/xo-reader2/include/xo/reader2/DGlobalEnv.hpp
+++ b/xo-reader2/include/xo/reader2/DGlobalEnv.hpp
@@ -71,7 +71,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DGlobalEnv * shallow_move(obj<AAllocator> mm) noexcept;
+            DGlobalEnv * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
             ///@}
diff --git a/xo-reader2/include/xo/reader2/env/IGCObject_DGlobalEnv.hpp b/xo-reader2/include/xo/reader2/env/IGCObject_DGlobalEnv.hpp
index f8ff90b7..6018a662 100644
--- a/xo-reader2/include/xo/reader2/env/IGCObject_DGlobalEnv.hpp
+++ b/xo-reader2/include/xo/reader2/env/IGCObject_DGlobalEnv.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DGlobalEnv & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DGlobalEnv & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DGlobalEnv & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-reader2/include/xo/reader2/parser/DSchematikaParser.hpp b/xo-reader2/include/xo/reader2/parser/DSchematikaParser.hpp
index da6862ab..07c85e4f 100644
--- a/xo-reader2/include/xo/reader2/parser/DSchematikaParser.hpp
+++ b/xo-reader2/include/xo/reader2/parser/DSchematikaParser.hpp
@@ -294,7 +294,7 @@ namespace xo {
 
             std::size_t shallow_size() const noexcept;
             /** not implemented (SchematikaParser not designed to be copyable) **/
-            DSchematikaParser * shallow_move(obj<AAllocator> mm) const noexcept;
+            DSchematikaParser * shallow_move(obj<ACollector> gc) noexcept;
             /** forward gc-aware children **/
             std::size_t forward_children(obj<ACollector> gc) noexcept;
 
diff --git a/xo-reader2/include/xo/reader2/parser/IGCObject_DSchematikaParser.hpp b/xo-reader2/include/xo/reader2/parser/IGCObject_DSchematikaParser.hpp
index e6fc39d9..f743e5cb 100644
--- a/xo-reader2/include/xo/reader2/parser/IGCObject_DSchematikaParser.hpp
+++ b/xo-reader2/include/xo/reader2/parser/IGCObject_DSchematikaParser.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DSchematikaParser & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DSchematikaParser & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DSchematikaParser & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-reader2/src/reader2/DGlobalEnv.cpp b/xo-reader2/src/reader2/DGlobalEnv.cpp
index 17a86798..243fc8d6 100644
--- a/xo-reader2/src/reader2/DGlobalEnv.cpp
+++ b/xo-reader2/src/reader2/DGlobalEnv.cpp
@@ -114,9 +114,9 @@ namespace xo {
         }
 
         DGlobalEnv *
-        DGlobalEnv::shallow_move(obj<AAllocator> mm) noexcept
+        DGlobalEnv::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for<DGlobalEnv>(this);
+            return gc.std_copy_for<DGlobalEnv>(this);
         }
 
         std::size_t
diff --git a/xo-reader2/src/reader2/DSchematikaParser.cpp b/xo-reader2/src/reader2/DSchematikaParser.cpp
index f26fe62a..35edc124 100644
--- a/xo-reader2/src/reader2/DSchematikaParser.cpp
+++ b/xo-reader2/src/reader2/DSchematikaParser.cpp
@@ -191,10 +191,13 @@ namespace xo {
         }
 
         DSchematikaParser *
-        DSchematikaParser::shallow_move(obj<AAllocator> mm) const noexcept
+        DSchematikaParser::shallow_move(obj<ACollector> gc) noexcept
         {
-            (void)mm;
+            (void)gc;
 
+            /** TODO: may be feasible to use gc.std_copy_for(this)
+             *  if/when DSchematikaParser is moveable
+             **/
             assert(false);
             return nullptr;
         }
diff --git a/xo-reader2/src/reader2/facet/IGCObject_DGlobalEnv.cpp b/xo-reader2/src/reader2/facet/IGCObject_DGlobalEnv.cpp
index f8edbb58..b31cadf6 100644
--- a/xo-reader2/src/reader2/facet/IGCObject_DGlobalEnv.cpp
+++ b/xo-reader2/src/reader2/facet/IGCObject_DGlobalEnv.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DGlobalEnv::shallow_move(DGlobalEnv & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DGlobalEnv::shallow_move(DGlobalEnv & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DGlobalEnv::forward_children(DGlobalEnv & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-reader2/src/reader2/facet/IGCObject_DSchematikaParser.cpp b/xo-reader2/src/reader2/facet/IGCObject_DSchematikaParser.cpp
index 8ba2349c..72c9d0e2 100644
--- a/xo-reader2/src/reader2/facet/IGCObject_DSchematikaParser.cpp
+++ b/xo-reader2/src/reader2/facet/IGCObject_DSchematikaParser.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DSchematikaParser::shallow_move(DSchematikaParser & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DSchematikaParser::shallow_move(DSchematikaParser & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DSchematikaParser::forward_children(DSchematikaParser & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-stringtable2/include/xo/stringtable2/DString.hpp b/xo-stringtable2/include/xo/stringtable2/DString.hpp
index bfcd30fa..cdb362d2 100644
--- a/xo-stringtable2/include/xo/stringtable2/DString.hpp
+++ b/xo-stringtable2/include/xo/stringtable2/DString.hpp
@@ -245,7 +245,7 @@ namespace xo {
             size_type shallow_size() const noexcept;
 
             /** clone string, using memory from allocator @p mm **/
-            DString * shallow_move(obj<AAllocator> mm) const noexcept;
+            DString * shallow_move(obj<ACollector> gc) noexcept;
 
             size_type forward_children(obj<ACollector> gc) noexcept;
             /** fixup child pointers (trivial for DString, no children)
diff --git a/xo-stringtable2/include/xo/stringtable2/DUniqueString.hpp b/xo-stringtable2/include/xo/stringtable2/DUniqueString.hpp
index d5b75626..c939f615 100644
--- a/xo-stringtable2/include/xo/stringtable2/DUniqueString.hpp
+++ b/xo-stringtable2/include/xo/stringtable2/DUniqueString.hpp
@@ -91,7 +91,7 @@ namespace xo {
             std::size_t shallow_size() const noexcept;
 
             /** clone unique string, using memory from allocator @p mm. **/
-            DUniqueString * shallow_move(obj<AAllocator> mm) const noexcept;
+            DUniqueString * shallow_move(obj<ACollector> gc) noexcept;
 
             /** fixup child pointers (trivial for DUniqueString, no gc-owned children **/
             std::size_t forward_children(obj<ACollector> gc) noexcept;
diff --git a/xo-stringtable2/include/xo/stringtable2/string/IGCObject_DString.hpp b/xo-stringtable2/include/xo/stringtable2/string/IGCObject_DString.hpp
index 6dc2ad1e..c4a71a50 100644
--- a/xo-stringtable2/include/xo/stringtable2/string/IGCObject_DString.hpp
+++ b/xo-stringtable2/include/xo/stringtable2/string/IGCObject_DString.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DString & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DString & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DString & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-stringtable2/include/xo/stringtable2/uniquestring/IGCObject_DUniqueString.hpp b/xo-stringtable2/include/xo/stringtable2/uniquestring/IGCObject_DUniqueString.hpp
index 1d6b8db8..27bc8252 100644
--- a/xo-stringtable2/include/xo/stringtable2/uniquestring/IGCObject_DUniqueString.hpp
+++ b/xo-stringtable2/include/xo/stringtable2/uniquestring/IGCObject_DUniqueString.hpp
@@ -55,7 +55,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DUniqueString & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DUniqueString & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DUniqueString & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-stringtable2/src/stringtable2/DString.cpp b/xo-stringtable2/src/stringtable2/DString.cpp
index f04db7f4..81f7780c 100644
--- a/xo-stringtable2/src/stringtable2/DString.cpp
+++ b/xo-stringtable2/src/stringtable2/DString.cpp
@@ -156,9 +156,12 @@ namespace xo {
         }
 
         DString *
-        DString::shallow_move(obj<AAllocator> mm) const noexcept
+        DString::shallow_move(obj<ACollector> gc) noexcept
         {
-            DString * copy = (DString *)mm.alloc_copy((std::byte *)this);
+            // note: not using gc.std_copy_for() here
+            //       b/c DString flexible array means not move-constructible
+
+            DString * copy = (DString *)gc.alloc_copy_for(this);
 
             if (copy) {
                 copy->capacity_ = capacity_;
diff --git a/xo-stringtable2/src/stringtable2/DUniqueString.cpp b/xo-stringtable2/src/stringtable2/DUniqueString.cpp
index dcf7cc53..057ee1f3 100644
--- a/xo-stringtable2/src/stringtable2/DUniqueString.cpp
+++ b/xo-stringtable2/src/stringtable2/DUniqueString.cpp
@@ -88,12 +88,16 @@ namespace xo {
         }
 
         DUniqueString *
-        DUniqueString::shallow_move(obj<AAllocator> mm) const noexcept
+        DUniqueString::shallow_move(obj<ACollector> gc) noexcept
         {
             // well-posed, but not expected to be used.
+            //
+            // Not using gc.std_copy_for() here because compiler doesn't know
+            // actual alloc size of a DUniqueString instance
+
             assert(false);
 
-            DUniqueString * copy = (DUniqueString *)mm.alloc_copy((std::byte *)this);
+            DUniqueString * copy = (DUniqueString *)gc.alloc_copy((std::byte *)this);
 
             if (copy) {
                 // Copy assignment not implemented in general
diff --git a/xo-stringtable2/src/stringtable2/IGCObject_DString.cpp b/xo-stringtable2/src/stringtable2/IGCObject_DString.cpp
index c3f6503a..01fc837c 100644
--- a/xo-stringtable2/src/stringtable2/IGCObject_DString.cpp
+++ b/xo-stringtable2/src/stringtable2/IGCObject_DString.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DString::shallow_move(DString & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DString::shallow_move(DString & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DString::forward_children(DString & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-stringtable2/src/stringtable2/IGCObject_DUniqueString.cpp b/xo-stringtable2/src/stringtable2/IGCObject_DUniqueString.cpp
index 034b9664..82e7c657 100644
--- a/xo-stringtable2/src/stringtable2/IGCObject_DUniqueString.cpp
+++ b/xo-stringtable2/src/stringtable2/IGCObject_DUniqueString.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DUniqueString::shallow_move(DUniqueString & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DUniqueString::shallow_move(DUniqueString & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DUniqueString::forward_children(DUniqueString & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-type/include/xo/type/DArrayType.hpp b/xo-type/include/xo/type/DArrayType.hpp
index a2594649..db827e80 100644
--- a/xo-type/include/xo/type/DArrayType.hpp
+++ b/xo-type/include/xo/type/DArrayType.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup xo-scm-arraytype-gcobject-facet **/
             ///@{
             std::size_t shallow_size() const noexcept;
-            DArrayType * shallow_move(obj<AAllocator> mm) noexcept;
+            DArrayType * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
             ///@}
 
diff --git a/xo-type/include/xo/type/DAtomicType.hpp b/xo-type/include/xo/type/DAtomicType.hpp
index 7661955c..b9daf767 100644
--- a/xo-type/include/xo/type/DAtomicType.hpp
+++ b/xo-type/include/xo/type/DAtomicType.hpp
@@ -43,7 +43,7 @@ namespace xo {
             /** @defgroup xo-scm-atomictype-gcobject-facet **/
             ///@{
             std::size_t shallow_size() const noexcept;
-            DAtomicType * shallow_move(obj<AAllocator> mm) noexcept;
+            DAtomicType * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
             ///@}
 
diff --git a/xo-type/include/xo/type/DFunctionType.hpp b/xo-type/include/xo/type/DFunctionType.hpp
index 328c93b3..5fbb93a7 100644
--- a/xo-type/include/xo/type/DFunctionType.hpp
+++ b/xo-type/include/xo/type/DFunctionType.hpp
@@ -64,7 +64,7 @@ namespace xo {
             /** @defgroup xo-scm-arraytype-gcobject-facet **/
             ///@{
             std::size_t shallow_size() const noexcept;
-            DFunctionType * shallow_move(obj<AAllocator> mm) noexcept;
+            DFunctionType * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
             ///@}
 
diff --git a/xo-type/include/xo/type/DListType.hpp b/xo-type/include/xo/type/DListType.hpp
index 2dfedb27..b2fd196b 100644
--- a/xo-type/include/xo/type/DListType.hpp
+++ b/xo-type/include/xo/type/DListType.hpp
@@ -50,7 +50,7 @@ namespace xo {
             /** @defgroup xo-scm-listtype-gcobject-facet **/
             ///@{
             std::size_t shallow_size() const noexcept;
-            DListType * shallow_move(obj<AAllocator> mm) noexcept;
+            DListType * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
             ///@}
 
diff --git a/xo-type/include/xo/type/array/IGCObject_DArrayType.hpp b/xo-type/include/xo/type/array/IGCObject_DArrayType.hpp
index 8c1bfeee..55c58b55 100644
--- a/xo-type/include/xo/type/array/IGCObject_DArrayType.hpp
+++ b/xo-type/include/xo/type/array/IGCObject_DArrayType.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DArrayType & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DArrayType & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DArrayType & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-type/include/xo/type/atomic/IGCObject_DAtomicType.hpp b/xo-type/include/xo/type/atomic/IGCObject_DAtomicType.hpp
index 00763e4a..6907e7cb 100644
--- a/xo-type/include/xo/type/atomic/IGCObject_DAtomicType.hpp
+++ b/xo-type/include/xo/type/atomic/IGCObject_DAtomicType.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DAtomicType & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DAtomicType & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DAtomicType & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-type/include/xo/type/function/IGCObject_DFunctionType.hpp b/xo-type/include/xo/type/function/IGCObject_DFunctionType.hpp
index 9c8727cd..f43b41ee 100644
--- a/xo-type/include/xo/type/function/IGCObject_DFunctionType.hpp
+++ b/xo-type/include/xo/type/function/IGCObject_DFunctionType.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DFunctionType & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DFunctionType & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DFunctionType & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-type/include/xo/type/list/IGCObject_DListType.hpp b/xo-type/include/xo/type/list/IGCObject_DListType.hpp
index 2459fff4..296779e9 100644
--- a/xo-type/include/xo/type/list/IGCObject_DListType.hpp
+++ b/xo-type/include/xo/type/list/IGCObject_DListType.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DListType & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DListType & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DListType & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-type/include/xo/type/typevar/DTypeVarRef.hpp b/xo-type/include/xo/type/typevar/DTypeVarRef.hpp
index 4ce9a667..f59f3f72 100644
--- a/xo-type/include/xo/type/typevar/DTypeVarRef.hpp
+++ b/xo-type/include/xo/type/typevar/DTypeVarRef.hpp
@@ -54,7 +54,7 @@ namespace xo {
             /** @defgroup xo-scm-atomictype-gcobject-facet **/
             ///@{
             std::size_t shallow_size() const noexcept;
-            DTypeVarRef * shallow_move(obj<AAllocator> mm) noexcept;
+            DTypeVarRef * shallow_move(obj<ACollector> gc) noexcept;
             std::size_t forward_children(obj<ACollector> gc) noexcept;
             ///@}
 
diff --git a/xo-type/include/xo/type/typevar/IGCObject_DTypeVarRef.hpp b/xo-type/include/xo/type/typevar/IGCObject_DTypeVarRef.hpp
index d0250871..e491cc35 100644
--- a/xo-type/include/xo/type/typevar/IGCObject_DTypeVarRef.hpp
+++ b/xo-type/include/xo/type/typevar/IGCObject_DTypeVarRef.hpp
@@ -53,7 +53,7 @@ namespace xo {
 
             // non-const methods
             /** move instance using allocator **/
-            static Opaque shallow_move(DTypeVarRef & self, obj<AAllocator> mm) noexcept;
+            static Opaque shallow_move(DTypeVarRef & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
             static size_type forward_children(DTypeVarRef & self, obj<ACollector> gc) noexcept;
             ///@}
diff --git a/xo-type/src/type/DArrayType.cpp b/xo-type/src/type/DArrayType.cpp
index b7c628af..52d25f5a 100644
--- a/xo-type/src/type/DArrayType.cpp
+++ b/xo-type/src/type/DArrayType.cpp
@@ -83,9 +83,9 @@ namespace xo {
         }
 
         DArrayType *
-        DArrayType::shallow_move(obj<AAllocator> mm) noexcept
+        DArrayType::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-type/src/type/DAtomicType.cpp b/xo-type/src/type/DAtomicType.cpp
index f25a159e..d4f0b166 100644
--- a/xo-type/src/type/DAtomicType.cpp
+++ b/xo-type/src/type/DAtomicType.cpp
@@ -61,9 +61,9 @@ namespace xo {
         }
 
         DAtomicType *
-        DAtomicType::shallow_move(obj<AAllocator> mm) noexcept
+        DAtomicType::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-type/src/type/DFunctionType.cpp b/xo-type/src/type/DFunctionType.cpp
index f9ac920e..8cb9001b 100644
--- a/xo-type/src/type/DFunctionType.cpp
+++ b/xo-type/src/type/DFunctionType.cpp
@@ -94,9 +94,9 @@ namespace xo {
         }
 
         DFunctionType *
-        DFunctionType::shallow_move(obj<AAllocator> mm) noexcept
+        DFunctionType::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-type/src/type/DListType.cpp b/xo-type/src/type/DListType.cpp
index 2906053d..487cc5fe 100644
--- a/xo-type/src/type/DListType.cpp
+++ b/xo-type/src/type/DListType.cpp
@@ -88,9 +88,9 @@ namespace xo {
         }
 
         DListType *
-        DListType::shallow_move(obj<AAllocator> mm) noexcept
+        DListType::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-type/src/type/DTypeVarRef.cpp b/xo-type/src/type/DTypeVarRef.cpp
index d618a2f2..a712174f 100644
--- a/xo-type/src/type/DTypeVarRef.cpp
+++ b/xo-type/src/type/DTypeVarRef.cpp
@@ -82,9 +82,9 @@ namespace xo {
         }
 
         DTypeVarRef *
-        DTypeVarRef::shallow_move(obj<AAllocator> mm) noexcept
+        DTypeVarRef::shallow_move(obj<ACollector> gc) noexcept
         {
-            return mm.std_copy_for(this);
+            return gc.std_copy_for(this);
         }
 
         std::size_t
diff --git a/xo-type/src/type/IGCObject_DArrayType.cpp b/xo-type/src/type/IGCObject_DArrayType.cpp
index c9375805..34319c27 100644
--- a/xo-type/src/type/IGCObject_DArrayType.cpp
+++ b/xo-type/src/type/IGCObject_DArrayType.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DArrayType::shallow_move(DArrayType & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DArrayType::shallow_move(DArrayType & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DArrayType::forward_children(DArrayType & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-type/src/type/IGCObject_DAtomicType.cpp b/xo-type/src/type/IGCObject_DAtomicType.cpp
index 3916d761..a0a92816 100644
--- a/xo-type/src/type/IGCObject_DAtomicType.cpp
+++ b/xo-type/src/type/IGCObject_DAtomicType.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DAtomicType::shallow_move(DAtomicType & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DAtomicType::shallow_move(DAtomicType & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DAtomicType::forward_children(DAtomicType & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-type/src/type/IGCObject_DFunctionType.cpp b/xo-type/src/type/IGCObject_DFunctionType.cpp
index 4c7c7c13..04e57607 100644
--- a/xo-type/src/type/IGCObject_DFunctionType.cpp
+++ b/xo-type/src/type/IGCObject_DFunctionType.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DFunctionType::shallow_move(DFunctionType & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DFunctionType::shallow_move(DFunctionType & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DFunctionType::forward_children(DFunctionType & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-type/src/type/IGCObject_DListType.cpp b/xo-type/src/type/IGCObject_DListType.cpp
index ff3820d0..fe721a34 100644
--- a/xo-type/src/type/IGCObject_DListType.cpp
+++ b/xo-type/src/type/IGCObject_DListType.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DListType::shallow_move(DListType & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DListType::shallow_move(DListType & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DListType::forward_children(DListType & self, obj<ACollector> gc) noexcept -> size_type
diff --git a/xo-type/src/type/IGCObject_DTypeVarRef.cpp b/xo-type/src/type/IGCObject_DTypeVarRef.cpp
index 9dc58dc0..f4f5d595 100644
--- a/xo-type/src/type/IGCObject_DTypeVarRef.cpp
+++ b/xo-type/src/type/IGCObject_DTypeVarRef.cpp
@@ -22,9 +22,9 @@ namespace xo {
         }
 
         auto
-        IGCObject_DTypeVarRef::shallow_move(DTypeVarRef & self, obj<AAllocator> mm) noexcept -> Opaque
+        IGCObject_DTypeVarRef::shallow_move(DTypeVarRef & self, obj<ACollector> gc) noexcept -> Opaque
         {
-            return self.shallow_move(mm);
+            return self.shallow_move(gc);
         }
         auto
         IGCObject_DTypeVarRef::forward_children(DTypeVarRef & self, obj<ACollector> gc) noexcept -> size_type