diff --git a/include/xo/object2/DArray.hpp b/include/xo/object2/DArray.hpp
index 99d1b3d..a455046 100644
--- a/include/xo/object2/DArray.hpp
+++ b/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/include/xo/object2/DBoolean.hpp b/include/xo/object2/DBoolean.hpp
index 34ffda1..31bf41b 100644
--- a/include/xo/object2/DBoolean.hpp
+++ b/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/include/xo/object2/DDictionary.hpp b/include/xo/object2/DDictionary.hpp
index 5e6ecae..219e783 100644
--- a/include/xo/object2/DDictionary.hpp
+++ b/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/include/xo/object2/DFloat.hpp b/include/xo/object2/DFloat.hpp
index b7d56e9..949883a 100644
--- a/include/xo/object2/DFloat.hpp
+++ b/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/include/xo/object2/DInteger.hpp b/include/xo/object2/DInteger.hpp
index 6a6194b..d3969b7 100644
--- a/include/xo/object2/DInteger.hpp
+++ b/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/include/xo/object2/DList.hpp b/include/xo/object2/DList.hpp
index 8fff47d..199ec6e 100644
--- a/include/xo/object2/DList.hpp
+++ b/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/include/xo/object2/DRuntimeError.hpp b/include/xo/object2/DRuntimeError.hpp
index 957c848..2ee9306 100644
--- a/include/xo/object2/DRuntimeError.hpp
+++ b/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/include/xo/object2/array/IGCObject_DArray.hpp b/include/xo/object2/array/IGCObject_DArray.hpp
index ab8a85f..58c202d 100644
--- a/include/xo/object2/array/IGCObject_DArray.hpp
+++ b/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/include/xo/object2/boolean/IGCObject_DBoolean.hpp b/include/xo/object2/boolean/IGCObject_DBoolean.hpp
index 5bc6e0c..3ca0392 100644
--- a/include/xo/object2/boolean/IGCObject_DBoolean.hpp
+++ b/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/include/xo/object2/dictionary/IGCObject_DDictionary.hpp b/include/xo/object2/dictionary/IGCObject_DDictionary.hpp
index 16fef8c..b6da10c 100644
--- a/include/xo/object2/dictionary/IGCObject_DDictionary.hpp
+++ b/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/include/xo/object2/error/IGCObject_DRuntimeError.hpp b/include/xo/object2/error/IGCObject_DRuntimeError.hpp
index 62cc610..42e273e 100644
--- a/include/xo/object2/error/IGCObject_DRuntimeError.hpp
+++ b/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/include/xo/object2/list/IGCObject_DList.hpp b/include/xo/object2/list/IGCObject_DList.hpp
index 780ebda..7218556 100644
--- a/include/xo/object2/list/IGCObject_DList.hpp
+++ b/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/include/xo/object2/number/IGCObject_DFloat.hpp b/include/xo/object2/number/IGCObject_DFloat.hpp
index b25e462..88d4d56 100644
--- a/include/xo/object2/number/IGCObject_DFloat.hpp
+++ b/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/include/xo/object2/number/IGCObject_DInteger.hpp b/include/xo/object2/number/IGCObject_DInteger.hpp
index a87f253..822ec16 100644
--- a/include/xo/object2/number/IGCObject_DInteger.hpp
+++ b/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/src/object2/DArray.cpp b/src/object2/DArray.cpp
index 2ae4ddc..a70213f 100644
--- a/src/object2/DArray.cpp
+++ b/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/src/object2/DBoolean.cpp b/src/object2/DBoolean.cpp
index cb25f9e..a8d5e85 100644
--- a/src/object2/DBoolean.cpp
+++ b/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/src/object2/DDictionary.cpp b/src/object2/DDictionary.cpp
index 739fced..2f25f1b 100644
--- a/src/object2/DDictionary.cpp
+++ b/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/src/object2/DFloat.cpp b/src/object2/DFloat.cpp
index f7f8ff3..4a9041c 100644
--- a/src/object2/DFloat.cpp
+++ b/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/src/object2/DInteger.cpp b/src/object2/DInteger.cpp
index 7cbcedf..600f48e 100644
--- a/src/object2/DInteger.cpp
+++ b/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/src/object2/DList.cpp b/src/object2/DList.cpp
index be86907..f17a53f 100644
--- a/src/object2/DList.cpp
+++ b/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/src/object2/DRuntimeError.cpp b/src/object2/DRuntimeError.cpp
index 1f34596..a52e1df 100644
--- a/src/object2/DRuntimeError.cpp
+++ b/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/src/object2/IGCObject_DArray.cpp b/src/object2/IGCObject_DArray.cpp
index 7cde63e..e4fa31c 100644
--- a/src/object2/IGCObject_DArray.cpp
+++ b/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/src/object2/IGCObject_DBoolean.cpp b/src/object2/IGCObject_DBoolean.cpp
index ef503af..2aed50e 100644
--- a/src/object2/IGCObject_DBoolean.cpp
+++ b/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/src/object2/IGCObject_DDictionary.cpp b/src/object2/IGCObject_DDictionary.cpp
index 9d4bae6..e8f291a 100644
--- a/src/object2/IGCObject_DDictionary.cpp
+++ b/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/src/object2/IGCObject_DFloat.cpp b/src/object2/IGCObject_DFloat.cpp
index a22a1b2..7625cac 100644
--- a/src/object2/IGCObject_DFloat.cpp
+++ b/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/src/object2/IGCObject_DInteger.cpp b/src/object2/IGCObject_DInteger.cpp
index 4f74e5f..9bb9bbf 100644
--- a/src/object2/IGCObject_DInteger.cpp
+++ b/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/src/object2/IGCObject_DList.cpp b/src/object2/IGCObject_DList.cpp
index 2512cc3..cbe8b71 100644
--- a/src/object2/IGCObject_DList.cpp
+++ b/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/src/object2/IGCObject_DRuntimeError.cpp b/src/object2/IGCObject_DRuntimeError.cpp
index cc75582..6917af7 100644
--- a/src/object2/IGCObject_DRuntimeError.cpp
+++ b/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