From a27b49d93dd20925dd176fc0222ff18db4919c2f Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Tue, 17 Feb 2026 14:42:17 -0500
Subject: [PATCH] xo-interpreter2 stack: define-expr's work at top-level

---
 include/xo/gc/PolyForwarderUtil.hpp | 66 +++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 include/xo/gc/PolyForwarderUtil.hpp

diff --git a/include/xo/gc/PolyForwarderUtil.hpp b/include/xo/gc/PolyForwarderUtil.hpp
new file mode 100644
index 0000000..19f99c9
--- /dev/null
+++ b/include/xo/gc/PolyForwarderUtil.hpp
@@ -0,0 +1,66 @@
+/** @file PolyForwarderUtil.hpp
+ *
+ *  @author Roland Conybeare, Feb 2026
+ **/
+
+#pragma once
+
+#include "Collector.hpp"
+#include <xo/facet/FacetRegistry.hpp>
+
+namespace xo {
+    namespace mm {
+
+        /** Utility class for forwarding support on
+         *  faceted object pointers that have some primary
+         *  facet _other_ than AGCObject.
+         *
+         *  For fop with AGCObject facet, with collector gc:
+         *
+         *    obj<ACollector> gc = ..;
+         *    obj<AGCObject> ptr = ..;
+         *
+         *    gc.forward_inplace(&ptr);
+         *
+         *  for fop with some other facet:
+         *
+         *    obj<ASomething> ptr = ..;
+         *    PolyForwarderUtil::forward_inplace(gc, &ptr);
+         *
+         *  or
+         *    poly_forward_inplace(gc, &ptr);
+         **/
+        class PolyForwarderUtil {
+        public:
+            template <typename AFacet, typename DRepr>
+            static void forward_inplace(obj<ACollector> gc, obj<AFacet,DRepr> * p_ptr) {
+                using xo::facet::FacetRegistry;
+
+                /**
+                 *    p_ptr
+                 *    v                       FacetRegistry
+                 *    +--------+---------+      .variant()        +-----------+---------+
+                 *    | AFacet | DRepr x |    ----------------->  | AGCobject | DRepr x |
+                 *    +--------+-------|-+                        +-----------+-------|-+
+                 *                     |                                              |
+                 *                     |  /-------------------------------------------/
+                 *                     |  |
+                 *                     v  v
+                 *                   +-------+
+                 *                   | DRepr |
+                 *                   +-------+
+                 **/
+
+                auto gco = FacetRegistry::instance().variant<AGCObject,AFacet>(*p_ptr);
+                gc.forward_inplace(gco.iface(), (void **)&(p_ptr->data_));
+            }
+        };
+
+        template <typename AFacet, typename DRepr>
+        void poly_forward_inplace(obj<ACollector> gc, obj<AFacet, DRepr> * p_ptr) {
+            PolyForwarderUtil::forward_inplace(gc, p_ptr);
+        }
+    } /*namespace mm*/
+} /*namespace xo*/
+
+/* end PolyForwarderUtil.hpp */