xo-facet: + builtin _drop() method for poly dtor call

xo-facet/CMakeLists.txt

@@ -27,6 +27,7 @@ set(SELF_LIB xo_facet)
 xo_add_headeronly_library(${SELF_LIB})
 
 # note: dependencies here must coordinate with cmake/xo_facetConfig.cmake.in
+xo_headeronly_dependency(${SELF_LIB} xo_arena)
 xo_headeronly_dependency(${SELF_LIB} xo_reflectutil)
 
 xo_install_library4(${SELF_LIB} ${PROJECT_NAME}Targets)

xo-facet/codegen/abstract_facet.hpp.j2

@@ -60,6 +60,8 @@ public:
     // const methods
     /** 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 **/
+    virtual void _drop(Opaque d) const noexcept = 0;
     {% for md in const_methods %}
     /** {{md.doc}} **/
     virtual {{md.return_type}} {{md.name}}({{md.args | args}}) {{md | qualifiers}} = 0;

xo-facet/codegen/iface_facet_any.hpp.j2

@@ -62,8 +62,11 @@ namespace {{facet_ns2}} {
 
         // from {{abstract_facet}}
 
-        // const methods
+        // builtin methods
         typeseq _typeseq() const noexcept override { return s_typeseq; }
+        [[noreturn]] void _drop(Opaque) const noexcept override { _fatal(); }
+
+        // const methods
         {% for md in const_methods %}
         [[noreturn]] {{md.return_type}} {{md.name}}({{md.args | argtypes}}) {{md | qualifiers}} override { _fatal(); }
         {% endfor %}

xo-facet/codegen/iface_facet_xfer.hpp.j2

@@ -49,8 +49,11 @@ namespace {{facet_ns2}} {
 
         // from {{abstract_facet}}
 
-        // const methods
+        // builtin methods
         typeseq _typeseq() const noexcept override { return s_typeseq; }
+        void _drop(Opaque d) const noexcept override { _dcast(d).~DRepr(); }
+
+        // const methods
         {% for md in const_methods %}
         {{md.return_type}} {{md.name}}({{md.args | args}}) {{md | qualifiers}} override {
             return I::{{md.name}}({{md.args | argnames}});

xo-facet/codegen/router_facet.hpp.j2

@@ -56,8 +56,11 @@ public:
     ///@{
     {% endif %}
 
-    // const methods
+    // builtin methods
     typeseq _typeseq() const noexcept { return O::iface()->_typeseq(); }
+    void _drop() const noexcept { O::iface()->_drop(O::data()); }
+
+    // const methods
     {% for md in const_methods %}
     {{md.return_type}} {{md.name}}({{md.args | argsnodata}}) {{md | qualifiers}} {
         return O::iface()->{{md.name}}({{md.args | argrouting}});