diff --git a/include/xo/expression2/DApplyExpr.hpp b/include/xo/expression2/DApplyExpr.hpp
index 0042d561..bc5cdc47 100644
--- a/include/xo/expression2/DApplyExpr.hpp
+++ b/include/xo/expression2/DApplyExpr.hpp
@@ -21,7 +21,7 @@ namespace xo {
          **/
         class DApplyExpr {
         public:
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -84,8 +84,7 @@ namespace xo {
             /** @defgroup scm-applyexpr-gcobject-facet **/
             ///@{
 
-            std::size_t shallow_size() const noexcept;
-            DApplyExpr * shallow_move(obj<ACollector> gc) noexcept;
+            DApplyExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DConstant.hpp b/include/xo/expression2/DConstant.hpp
index 2c878ea9..e81a7b2d 100644
--- a/include/xo/expression2/DConstant.hpp
+++ b/include/xo/expression2/DConstant.hpp
@@ -8,7 +8,7 @@
 #include "Expression.hpp"
 #include "TypeRef.hpp"
 #include "exprtype.hpp"
-#include <xo/alloc2/Collector.hpp>
+//#include <xo/alloc2/Collector.hpp>
 #include <xo/alloc2/GCObject.hpp>
 #include <xo/alloc2/GCObjectVisitor.hpp>
 #include <xo/reflect/TaggedPtr.hpp>
@@ -22,7 +22,7 @@ namespace xo {
         public:
             using TaggedPtr = xo::reflect::TaggedPtr;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObject = xo::mm::AGCObject;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
@@ -64,8 +64,7 @@ namespace xo {
             /** @defgroup scm-constant-gcobject-facet **/
             ///@{
 
-            size_t shallow_size() const noexcept;
-            DConstant * shallow_move(obj<ACollector> gc) noexcept;
+            DConstant * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DDefineExpr.hpp b/include/xo/expression2/DDefineExpr.hpp
index f1528531..474a4122 100644
--- a/include/xo/expression2/DDefineExpr.hpp
+++ b/include/xo/expression2/DDefineExpr.hpp
@@ -74,8 +74,7 @@ namespace xo {
             /** @defgroup scm-defineexpr-gcobject-facet **/
             ///@{
 
-            std::size_t shallow_size() const noexcept;
-            DDefineExpr * shallow_move(obj<ACollector> gc) noexcept;
+            DDefineExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DGlobalSymtab.hpp b/include/xo/expression2/DGlobalSymtab.hpp
index a24c0bdc..b3840a69 100644
--- a/include/xo/expression2/DGlobalSymtab.hpp
+++ b/include/xo/expression2/DGlobalSymtab.hpp
@@ -30,7 +30,7 @@ namespace xo {
             using value_type = Binding;
             using ArenaHashMapConfig = xo::map::ArenaHashMapConfig;
             using repr_type = xo::map::DArenaHashMap<key_type, Binding::slot_type>;
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObject = xo::mm::AGCObject;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
@@ -115,7 +115,7 @@ namespace xo {
             /** @defgroup scm-globalsymtab-gcobject-facet gcobject facet **/
             ///@{
 
-            DGlobalSymtab * shallow_move(obj<ACollector> gc) noexcept;
+            DGlobalSymtab * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DIfElseExpr.hpp b/include/xo/expression2/DIfElseExpr.hpp
index b27c9ade..04a354dd 100644
--- a/include/xo/expression2/DIfElseExpr.hpp
+++ b/include/xo/expression2/DIfElseExpr.hpp
@@ -8,7 +8,7 @@
 #include "Expression.hpp"
 #include "TypeRef.hpp"
 #include "exprtype.hpp"
-#include <xo/alloc2/Collector.hpp>
+//#include <xo/alloc2/Collector.hpp>
 #include <xo/alloc2/GCObjectVisitor.hpp>
 #include <xo/alloc2/Allocator.hpp>
 #include <string>
@@ -21,7 +21,7 @@ namespace xo {
          **/
         class DIfElseExpr {
         public:
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -98,8 +98,7 @@ namespace xo {
             /** @defgroup scm-ifelseexpr-gcobject-facet **/
             ///@{
 
-            std::size_t shallow_size() const noexcept;
-            DIfElseExpr * shallow_move(obj<ACollector> gc) noexcept;
+            DIfElseExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DLambdaExpr.hpp b/include/xo/expression2/DLambdaExpr.hpp
index 2a507497..e4b0296d 100644
--- a/include/xo/expression2/DLambdaExpr.hpp
+++ b/include/xo/expression2/DLambdaExpr.hpp
@@ -21,7 +21,7 @@ namespace xo {
          **/
         class DLambdaExpr {
         public:
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -87,7 +87,7 @@ namespace xo {
             ///@{
 
             std::size_t shallow_size() const noexcept;
-            DLambdaExpr * shallow_move(obj<ACollector> gc) noexcept;
+            DLambdaExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DLocalSymtab.hpp b/include/xo/expression2/DLocalSymtab.hpp
index f389c3ea..081742b0 100644
--- a/include/xo/expression2/DLocalSymtab.hpp
+++ b/include/xo/expression2/DLocalSymtab.hpp
@@ -20,7 +20,7 @@ namespace xo {
         public:
             using DArray = xo::scm::DArray;
             using ppindentinfo = xo::print::ppindentinfo;
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObject = xo::mm::AGCObject;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
@@ -99,7 +99,7 @@ namespace xo {
             /** @defgroup xo-localsymtab-gcobject-facet gcobject facet **/
             ///@{
 
-            DLocalSymtab * shallow_move(obj<ACollector> gc) noexcept;
+            DLocalSymtab * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DSequenceExpr.hpp b/include/xo/expression2/DSequenceExpr.hpp
index 76a8bec0..4a103e0e 100644
--- a/include/xo/expression2/DSequenceExpr.hpp
+++ b/include/xo/expression2/DSequenceExpr.hpp
@@ -23,7 +23,7 @@ namespace xo {
          **/
         class DSequenceExpr {
         public:
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -74,8 +74,7 @@ namespace xo {
             /** @defgroup scm-sequenceexpr-gcobject-facet gcobject facet methods **/
             ///@{
 
-            std::size_t shallow_size() const noexcept;
-            DSequenceExpr * shallow_move(obj<ACollector> gc) noexcept;
+            DSequenceExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DTypename.hpp b/include/xo/expression2/DTypename.hpp
index 2e35c9e3..7ddacd21 100644
--- a/include/xo/expression2/DTypename.hpp
+++ b/include/xo/expression2/DTypename.hpp
@@ -24,7 +24,7 @@ namespace xo {
         class DTypename {
         public:
             using ppindentinfo = xo::print::ppindentinfo;
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AGCObject = xo::mm::AGCObject;
             using AAllocator = xo::mm::AAllocator;
@@ -55,8 +55,7 @@ namespace xo {
             /** @defgroup scm-typename-gcobject-facet **/
             ///@{
 
-            size_t shallow_size() const noexcept;
-            DTypename * shallow_move(obj<ACollector> gc) noexcept;
+            DTypename * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DVarRef.hpp b/include/xo/expression2/DVarRef.hpp
index db85d558..002e511a 100644
--- a/include/xo/expression2/DVarRef.hpp
+++ b/include/xo/expression2/DVarRef.hpp
@@ -21,7 +21,7 @@ namespace xo {
         class DVarRef {
         public:
             using ppindentinfo = xo::print::ppindentinfo;
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -56,8 +56,7 @@ namespace xo {
             /** @defgroup scm-variable-gcobject-facet **/
             ///@{
 
-            size_t shallow_size() const noexcept;
-            DVarRef * shallow_move(obj<ACollector> gc) noexcept;
+            DVarRef * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/DVariable.hpp b/include/xo/expression2/DVariable.hpp
index 2e74fbcc..5813ae1b 100644
--- a/include/xo/expression2/DVariable.hpp
+++ b/include/xo/expression2/DVariable.hpp
@@ -22,7 +22,7 @@ namespace xo {
         class DVariable {
         public:
             using ppindentinfo = xo::print::ppindentinfo;
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -64,8 +64,7 @@ namespace xo {
             /** @defgroup scm-variable-gcobject-facet **/
             ///@{
 
-            size_t shallow_size() const noexcept;
-            DVariable * shallow_move(obj<ACollector> gc) noexcept;
+            DVariable * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
             void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
diff --git a/include/xo/expression2/define/IGCObject_DDefineExpr.hpp b/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
index 8cb5fe13..6a233f92 100644
--- a/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
+++ b/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DDefineExpr & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DDefineExpr & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp b/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
index 068f9b12..399d9398 100644
--- a/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
+++ b/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DApplyExpr & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DApplyExpr & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/detail/IGCObject_DConstant.hpp b/include/xo/expression2/detail/IGCObject_DConstant.hpp
index a909f00f..b2e624be 100644
--- a/include/xo/expression2/detail/IGCObject_DConstant.hpp
+++ b/include/xo/expression2/detail/IGCObject_DConstant.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DConstant & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DConstant & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp b/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
index ca0d078a..80a49f22 100644
--- a/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
+++ b/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DIfElseExpr & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DIfElseExpr & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp b/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
index bd13504d..5decc2a0 100644
--- a/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
+++ b/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DLambdaExpr & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DLambdaExpr & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp b/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
index 2801853a..54bab050 100644
--- a/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
+++ b/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DSequenceExpr & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DSequenceExpr & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/detail/IGCObject_DVarRef.hpp b/include/xo/expression2/detail/IGCObject_DVarRef.hpp
index 74693209..98c65aab 100644
--- a/include/xo/expression2/detail/IGCObject_DVarRef.hpp
+++ b/include/xo/expression2/detail/IGCObject_DVarRef.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DVarRef & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DVarRef & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp b/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
index a1aebbc4..334c0ea9 100644
--- a/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
+++ b/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DGlobalSymtab & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DGlobalSymtab & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp b/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
index 61d159b2..c7890a79 100644
--- a/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
+++ b/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DLocalSymtab & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DLocalSymtab & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/typename/IGCObject_DTypename.hpp b/include/xo/expression2/typename/IGCObject_DTypename.hpp
index fbf46356..e8946864 100644
--- a/include/xo/expression2/typename/IGCObject_DTypename.hpp
+++ b/include/xo/expression2/typename/IGCObject_DTypename.hpp
@@ -51,8 +51,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DTypename & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DTypename & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/include/xo/expression2/variable/IGCObject_DVariable.hpp b/include/xo/expression2/variable/IGCObject_DVariable.hpp
index 1bf0b86c..3a31f155 100644
--- a/include/xo/expression2/variable/IGCObject_DVariable.hpp
+++ b/include/xo/expression2/variable/IGCObject_DVariable.hpp
@@ -53,8 +53,9 @@ namespace xo {
             // const methods
 
             // non-const methods
-            /** move instance using collector **/
-            static Opaque shallow_move(DVariable & self, obj<ACollector> gc) noexcept;
+            /** move instance using object visitor.
+Arguably abusing the word 'visitor' here **/
+            static Opaque gco_shallow_move(DVariable & self, obj<AGCObjectVisitor> gc) noexcept;
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
diff --git a/src/expression2/DApplyExpr.cpp b/src/expression2/DApplyExpr.cpp
index 18b9b60a..2776b438 100644
--- a/src/expression2/DApplyExpr.cpp
+++ b/src/expression2/DApplyExpr.cpp
@@ -104,13 +104,8 @@ namespace xo {
 
         // ----- gcobject facet -----
 
-        std::size_t
-        DApplyExpr::shallow_size() const noexcept {
-            return sizeof(DApplyExpr) + (n_args_ * sizeof(obj<AExpression>));
-        }
-
         DApplyExpr *
-        DApplyExpr::shallow_move(obj<ACollector> gc) noexcept {
+        DApplyExpr::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept {
             // note: not using ACollector.std_copy_for() here,
             //       flexible array -> not move-constructible
 
diff --git a/src/expression2/DConstant.cpp b/src/expression2/DConstant.cpp
index bbf86183..19805cb5 100644
--- a/src/expression2/DConstant.cpp
+++ b/src/expression2/DConstant.cpp
@@ -71,14 +71,8 @@ namespace xo {
             return nullptr;
         }
 
-        std::size_t
-        DConstant::shallow_size() const noexcept
-        {
-            return sizeof(DConstant);
-        }
-
         DConstant *
-        DConstant::shallow_move(obj<ACollector> gc) noexcept
+        DConstant::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/DDefineExpr.cpp b/src/expression2/DDefineExpr.cpp
index 69ce84e0..ba481805 100644
--- a/src/expression2/DDefineExpr.cpp
+++ b/src/expression2/DDefineExpr.cpp
@@ -78,14 +78,8 @@ namespace xo {
 
         // ----- GCObject facet -----
 
-        std::size_t
-        DDefineExpr::shallow_size() const noexcept
-        {
-            return sizeof(*this);
-        }
-
         DDefineExpr *
-        DDefineExpr::shallow_move(obj<ACollector> gc) noexcept
+        DDefineExpr::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/DGlobalSymtab.cpp b/src/expression2/DGlobalSymtab.cpp
index 10f65ea2..f5df4a4c 100644
--- a/src/expression2/DGlobalSymtab.cpp
+++ b/src/expression2/DGlobalSymtab.cpp
@@ -263,7 +263,7 @@ namespace xo {
         // ----- gcobject facet -----
 
         DGlobalSymtab *
-        DGlobalSymtab::shallow_move(obj<ACollector> gc) noexcept
+        DGlobalSymtab::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/DIfElseExpr.cpp b/src/expression2/DIfElseExpr.cpp
index c44a7ebd..b8758387 100644
--- a/src/expression2/DIfElseExpr.cpp
+++ b/src/expression2/DIfElseExpr.cpp
@@ -82,14 +82,8 @@ namespace xo {
 
         // GCObject facet
 
-        std::size_t
-        DIfElseExpr::shallow_size() const noexcept
-        {
-            return sizeof(DIfElseExpr);
-        }
-
         DIfElseExpr *
-        DIfElseExpr::shallow_move(obj<ACollector> gc) noexcept
+        DIfElseExpr::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/DLambdaExpr.cpp b/src/expression2/DLambdaExpr.cpp
index 349ccd99..c73ccc8a 100644
--- a/src/expression2/DLambdaExpr.cpp
+++ b/src/expression2/DLambdaExpr.cpp
@@ -141,7 +141,7 @@ namespace xo {
         }
 
         DLambdaExpr *
-        DLambdaExpr::shallow_move(obj<ACollector> gc) noexcept {
+        DLambdaExpr::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept {
             return gc.std_move_for(this);
         }
 
diff --git a/src/expression2/DLocalSymtab.cpp b/src/expression2/DLocalSymtab.cpp
index 017fb1d7..1fa1afd8 100644
--- a/src/expression2/DLocalSymtab.cpp
+++ b/src/expression2/DLocalSymtab.cpp
@@ -113,7 +113,7 @@ namespace xo {
         // ----- gcobject facet -----
 
         DLocalSymtab *
-        DLocalSymtab::shallow_move(obj<ACollector> gc) noexcept
+        DLocalSymtab::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/DSequenceExpr.cpp b/src/expression2/DSequenceExpr.cpp
index 2dc153f0..a180a5fb 100644
--- a/src/expression2/DSequenceExpr.cpp
+++ b/src/expression2/DSequenceExpr.cpp
@@ -113,14 +113,8 @@ namespace xo {
 
         // gc hooks for IGCObject_DSequenceExpr
 
-        std::size_t
-        DSequenceExpr::shallow_size() const noexcept
-        {
-            return sizeof(DSequenceExpr);
-        }
-
         DSequenceExpr *
-        DSequenceExpr::shallow_move(obj<ACollector> gc) noexcept
+        DSequenceExpr::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/DTypename.cpp b/src/expression2/DTypename.cpp
index 15e7dbdb..da73f28f 100644
--- a/src/expression2/DTypename.cpp
+++ b/src/expression2/DTypename.cpp
@@ -40,14 +40,8 @@ namespace xo {
             : name_{name}, type_{type}
         {}
 
-        size_t
-        DTypename::shallow_size() const noexcept
-        {
-            return sizeof(DTypename);
-        }
-
         DTypename *
-        DTypename::shallow_move(obj<ACollector> gc) noexcept
+        DTypename::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/DVarRef.cpp b/src/expression2/DVarRef.cpp
index 6cdea4e5..57a39153 100644
--- a/src/expression2/DVarRef.cpp
+++ b/src/expression2/DVarRef.cpp
@@ -58,14 +58,8 @@ namespace xo {
 
         // gcobject facet
 
-        std::size_t
-        DVarRef::shallow_size() const noexcept
-        {
-            return sizeof(DVarRef);
-        }
-
         DVarRef *
-        DVarRef::shallow_move(obj<ACollector> gc) noexcept
+        DVarRef::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/DVariable.cpp b/src/expression2/DVariable.cpp
index 9ab2f8bd..209764cd 100644
--- a/src/expression2/DVariable.cpp
+++ b/src/expression2/DVariable.cpp
@@ -38,14 +38,8 @@ namespace xo {
             typeref_.resolve(td);
         }
 
-        size_t
-        DVariable::shallow_size() const noexcept
-        {
-            return sizeof(DVariable);
-        }
-
         DVariable *
-        DVariable::shallow_move(obj<ACollector> gc) noexcept
+        DVariable::gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept
         {
             return gc.std_move_for(this);
         }
diff --git a/src/expression2/IGCObject_DApplyExpr.cpp b/src/expression2/IGCObject_DApplyExpr.cpp
index 9b5fc735..d2574d64 100644
--- a/src/expression2/IGCObject_DApplyExpr.cpp
+++ b/src/expression2/IGCObject_DApplyExpr.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DApplyExpr::shallow_move(DApplyExpr & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DApplyExpr::gco_shallow_move(DApplyExpr & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DApplyExpr::visit_gco_children(DApplyExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DConstant.cpp b/src/expression2/IGCObject_DConstant.cpp
index 3e350102..be6f583d 100644
--- a/src/expression2/IGCObject_DConstant.cpp
+++ b/src/expression2/IGCObject_DConstant.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DConstant::shallow_move(DConstant & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DConstant::gco_shallow_move(DConstant & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DConstant::visit_gco_children(DConstant & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DDefineExpr.cpp b/src/expression2/IGCObject_DDefineExpr.cpp
index 34c59e93..f2ea0747 100644
--- a/src/expression2/IGCObject_DDefineExpr.cpp
+++ b/src/expression2/IGCObject_DDefineExpr.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DDefineExpr::shallow_move(DDefineExpr & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DDefineExpr::gco_shallow_move(DDefineExpr & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DDefineExpr::visit_gco_children(DDefineExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DGlobalSymtab.cpp b/src/expression2/IGCObject_DGlobalSymtab.cpp
index 1e78de47..3070a26c 100644
--- a/src/expression2/IGCObject_DGlobalSymtab.cpp
+++ b/src/expression2/IGCObject_DGlobalSymtab.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DGlobalSymtab::shallow_move(DGlobalSymtab & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DGlobalSymtab::gco_shallow_move(DGlobalSymtab & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DGlobalSymtab::visit_gco_children(DGlobalSymtab & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DIfElseExpr.cpp b/src/expression2/IGCObject_DIfElseExpr.cpp
index 0db6f160..6f788e03 100644
--- a/src/expression2/IGCObject_DIfElseExpr.cpp
+++ b/src/expression2/IGCObject_DIfElseExpr.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DIfElseExpr::shallow_move(DIfElseExpr & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DIfElseExpr::gco_shallow_move(DIfElseExpr & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DIfElseExpr::visit_gco_children(DIfElseExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DLambdaExpr.cpp b/src/expression2/IGCObject_DLambdaExpr.cpp
index a9ad37aa..b4706c56 100644
--- a/src/expression2/IGCObject_DLambdaExpr.cpp
+++ b/src/expression2/IGCObject_DLambdaExpr.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DLambdaExpr::shallow_move(DLambdaExpr & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DLambdaExpr::gco_shallow_move(DLambdaExpr & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DLambdaExpr::visit_gco_children(DLambdaExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DLocalSymtab.cpp b/src/expression2/IGCObject_DLocalSymtab.cpp
index 7384e17a..5e37d826 100644
--- a/src/expression2/IGCObject_DLocalSymtab.cpp
+++ b/src/expression2/IGCObject_DLocalSymtab.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DLocalSymtab::shallow_move(DLocalSymtab & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DLocalSymtab::gco_shallow_move(DLocalSymtab & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DLocalSymtab::visit_gco_children(DLocalSymtab & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DSequenceExpr.cpp b/src/expression2/IGCObject_DSequenceExpr.cpp
index 8660f506..1f92c2e2 100644
--- a/src/expression2/IGCObject_DSequenceExpr.cpp
+++ b/src/expression2/IGCObject_DSequenceExpr.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DSequenceExpr::shallow_move(DSequenceExpr & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DSequenceExpr::gco_shallow_move(DSequenceExpr & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DSequenceExpr::visit_gco_children(DSequenceExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DTypename.cpp b/src/expression2/IGCObject_DTypename.cpp
index 478b2005..ca21870a 100644
--- a/src/expression2/IGCObject_DTypename.cpp
+++ b/src/expression2/IGCObject_DTypename.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DTypename::shallow_move(DTypename & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DTypename::gco_shallow_move(DTypename & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DTypename::visit_gco_children(DTypename & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/IGCObject_DVarRef.cpp b/src/expression2/IGCObject_DVarRef.cpp
index 7035db1e..68d6e1d2 100644
--- a/src/expression2/IGCObject_DVarRef.cpp
+++ b/src/expression2/IGCObject_DVarRef.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DVarRef::shallow_move(DVarRef & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DVarRef::gco_shallow_move(DVarRef & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DVarRef::visit_gco_children(DVarRef & self, obj<AGCObjectVisitor> fn) noexcept -> void
diff --git a/src/expression2/facet/IGCObject_DVariable.cpp b/src/expression2/facet/IGCObject_DVariable.cpp
index a6370f56..0a91bfb2 100644
--- a/src/expression2/facet/IGCObject_DVariable.cpp
+++ b/src/expression2/facet/IGCObject_DVariable.cpp
@@ -16,9 +16,9 @@
 namespace xo {
     namespace scm {
         auto
-        IGCObject_DVariable::shallow_move(DVariable & self, obj<ACollector> gc) noexcept -> Opaque
+        IGCObject_DVariable::gco_shallow_move(DVariable & self, obj<AGCObjectVisitor> gc) noexcept -> Opaque
         {
-            return self.shallow_move(gc);
+            return self.gco_shallow_move(gc);
         }
         auto
         IGCObject_DVariable::visit_gco_children(DVariable & self, obj<AGCObjectVisitor> fn) noexcept -> void