refactor: + xo-stringtable2 w/ DString impl

include/xo/alloc2/CollectorTypeRegistry.hpp

@@ -0,0 +1,74 @@
+/** @file CollectorTypeRegistry.hpp
+ *
+ *  @brief Runtime type registration for gc-aware types
+ *
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#pragma once
+
+#include "Collector.hpp"
+#include <functional>
+
+namespace xo {
+    namespace mm {
+        /** @class CollectorTypeRegistry
+         *
+         *  @brief Runtime registry for gc-aware types
+         *
+         *  Singleton to remember known gc-aware types;
+         *  use to simplify registering such types
+         *  with a collector instance.
+         *
+         *  Remark: splitting work here between
+         *  1. static initializer work: tracking gc-aware types,
+         *  2. runtime post-configuration work: report
+         *     gc-aware types to GC instances
+         *
+         *  Use:
+         *  1. subsystem foo provides function foo_register_types(obj<ACollector> gc)
+         *     Function calls
+         *       gc.install_type(impl_for<AGCObject, DQuux>())
+         *     for each gc-aware type provided by subsystem foo
+         *
+         *     Example: in file xo-object2/src/object2/object2_register_types.cpp, see
+         *       object2_register_types()
+         *
+         *  2. during subsystem init, call
+         *       CollectorTypeRegistry::instance().register_types(&foo_register_types);
+         *
+         *     Example: in file xo-object2/src/object2/init_object2.cpp, see
+         *       InitSubsys<S_object2_tag>::init()
+         *
+         *  3. during Collector setup, call
+         *       obj<ACollector> gc = ...;
+         *       CollectorTypeRegistry::instance().install_types(gc);
+         *
+         *    Example: in file xo-object2/utest/X1Collector.test.cpp
+         *       TEST_CASE("x1")
+         **/
+        class CollectorTypeRegistry {
+        public:
+            using init_function_type = std::function<bool (obj<ACollector>)>;
+
+        public:
+            /** singleton instance **/
+            static CollectorTypeRegistry & instance();
+
+            /** remember a gc-aware type-registration function **/
+            void register_types(init_function_type init_fn);
+
+            /** register known GC-aware types with @p gc.
+             *  Calls @c gc.isntall_type() for each
+             *  such type.
+             **/
+            bool install_types(obj<ACollector> gc);
+
+        private:
+            /** initialization steps for a new Collector instance **/
+            std::vector<init_function_type> init_seq_v_;
+        };
+    }
+}
+
+/* end CollectorTypeRegistry.hpp */