refactor: use GCObjectVisitor api w/ gco_shallow_move

idl/GCObject.json5

@@ -64,11 +64,14 @@
     nonconst_methods: [
         // Opaque shallow_move(obj<ACollector>) noexcept
         {
-            name: "shallow_move",
-            doc: ["move instance using collector"],
+            name: "gco_shallow_move",
+            doc: [
+                "move instance using object visitor.",
+                "Arguably abusing the word 'visitor' here",
+            ],
             return_type: "Opaque",
             args:[
-                {type: "obj<ACollector>", name: "gc"},
+                {type: "obj<AGCObjectVisitor>", name: "gc"},
             ],
             const: true,
             noexcept: true,

idl/GCObjectVisitor.json5

@@ -88,9 +88,25 @@
         },
     ],
     router_facet_explicit_content: [
+        "/** convenience: allocate copy for typed pointer **/",
+        "template <typename T>",
+        "void * alloc_copy_for(const T * src) noexcept {",
+        "    return O::iface()->alloc_copy(O::data(), (std::byte *)const_cast<T *>(src));",
+        "}",
         "",
-        "/** visit forward faceted object child pointer in place.",
-        "    Defined in RGCObject.hpp to avoid #include cycle",
+        "/** convenience: move typed pointer **/",
+        "template <typename T>",
+        "T * std_move_for(T * src) noexcept {",
+        "    void * mem = this->alloc_copy_for(src);",
+        "    if (mem) {",
+        "        return new (mem) T(std::move(*src));",
+        "    }",
+        "    return nullptr;",
+        "}",
+        "",
+        "/** visit a gcobject child pointer in place.",
+        "    Defined in RCollector_aux.hpp to avoid #include cycle",
+        "    (for historical reasons - coul d be in RGCObject_aux.hpp?)",
         " **/",
         "template <typename DRepr>",
         "void visit_child(xo::facet::obj<AGCObject,DRepr> * p_obj);",