Overridable metamethods from lua

Source/LuaBridge/detail/CFunctions.h

@@ -147,10 +147,44 @@ inline bool is_metamethod(std::string_view method_name)
         "__unm"
     );
 
+    if (method_name.size() <= 2 || method_name[0] != '_' || method_name[1] != '_')
+        return false;
+
     auto result = std::lower_bound(metamethods.begin(), metamethods.end(), method_name);
     return result != metamethods.end() && *result == method_name;
 }
 
+/**
+ * @brief Make super method name.
+ */
+inline std::string make_super_method_name(const char* name)
+{
+    LUABRIDGE_ASSERT(name != nullptr);
+
+    return (std::string_view(name).find("_") == 0u)
+        ? (std::string("super") + name)
+        : (std::string("super_") + name);
+}
+
+//=================================================================================================
+/**
+ * @brief Make super method name.
+ */
+inline Options get_class_options(lua_State* L, int index)
+{
+    LUABRIDGE_ASSERT(lua_istable(L, index)); // Stack: mt
+
+    Options options = defaultOptions;
+
+    lua_rawgetp(L, index, getClassOptionsKey()); // Stack: mt, ifb (may be nil)
+    if (lua_isnumber(L, -1))
+        options = Options::fromUnderlying(lua_tointeger(L, -1));
+
+    lua_pop(L, 1);
+
+    return options;
+}
+
 //=================================================================================================
 /**
  * @brief __index metamethod for a namespace or class static and non-static members.
@@ -196,28 +230,16 @@ inline int index_metamethod(lua_State* L)
 
     // Protect internal meta methods
     const char* key = lua_tostring(L, 2);
-    if (key != nullptr)
+    if (key != nullptr && is_metamethod(key))
     {
-        const auto name = std::string_view(key);
-        if (name.size() > 2 && name[0] == '_' && name[1] == '_' && is_metamethod(name))
-        {
-            lua_pushnil(L);
-            return 1;
-        }
+        lua_pushnil(L);
+        return 1;
     }
 
     for (;;)
     {
-        // Obtain class options
-        Options options = defaultOptions;
-
-        lua_rawgetp(L, -1, getClassOptionsKey()); // Stack: mt, ifb (may be nil)
-        if (lua_isnumber(L, -1))
-            options = Options::fromUnderlying(lua_tointeger(L, -1));
-
-        lua_pop(L, 1);
-
         // If we allow method overriding, we need to prioritise it
+        const Options options = get_class_options(L, -1); // Stack: mt
         if (options.test(allowOverridingMethods))
         {
             if (auto result = try_call_index_fallback(L))
@@ -289,15 +311,18 @@ inline int index_metamethod(lua_State* L)
 
 inline std::optional<int> try_call_newindex_fallback(lua_State* L, const char* key)
 {
+    LUABRIDGE_ASSERT(key != nullptr);
     LUABRIDGE_ASSERT(lua_istable(L, -1)); // Stack: mt
 
-    lua_rawgetp(L, -1, getNewIndexFallbackKey()); // Stack: mt, nifb (may be nil)
+    lua_rawgetp(L, -1, getNewIndexFallbackKey()); // Stack: mt, nifb | nil
     if (! lua_iscfunction(L, -1))
     {
         lua_pop(L, 1); // Stack: mt
         return std::nullopt;
     }
 
+    const bool is_key_metamethod = is_metamethod(key);
+
     lua_pushvalue(L, -2); // Stack: mt, nifb, mt
 
     for (;;)
@@ -318,49 +343,49 @@ inline std::optional<int> try_call_newindex_fallback(lua_State* L, const char* k
         lua_pushvalue(L, 2); // Stack: mt, nifb, mt, ct, field name
         lua_rawget(L, -2); // Stack: mt, nifb, mt, ct, field | nil
 
-        if (! lua_isnil(L, -1)) // Stack: mt, nifb, mt, ct, nil
+        if (! lua_isnil(L, -1)) // Stack: mt, nifb, mt, ct, field
         {
-            Options options = defaultOptions;
-            lua_rawgetp(L, -2, getClassOptionsKey()); // Stack: mt, nifb, mt, ct, field, opt | nil
-            if (lua_isnumber(L, -1))
-                options = Options::fromUnderlying(lua_tointeger(L, -1));
-            lua_pop(L, 1); // Stack: mt, nifb, mt, ct, field
-
+            // Obtain class options
+            const Options options = get_class_options(L, -2); // Stack: mt, nifb, mt, ct, field,
             if (! options.test(allowOverridingMethods))
-            {
-                lua_pop(L, 5); // Stack: -
                 luaL_error(L, "immutable member '%s'", key);
-                return 0;
-            }
 
             lua_getmetatable(L, 1); // Stack: mt, nifb, mt, ct, field, mt2
             lua_pushvalue(L, -2);  // Stack: mt, nifb, mt, ct, field, mt2, field
-            rawsetfield(L, -2, (std::string("super_") + key).c_str()); // Stack: mt, nifb, mt, ct, field, mt2
+            rawsetfield(L, -2, make_super_method_name(key).c_str()); // Stack: mt, nifb, mt, ct, field, mt2
 
-            lua_pop(L, 3); // Stack: mt, nifb, mt
+            lua_pop(L, 2); // Stack: mt, nifb, mt, ct
             break;
         }
 
-        lua_pop(L, 2); // Stack: mt, nifb, mt
+        lua_pop(L, 1); // Stack: mt, nifb, mt, ct
 
-        lua_rawgetp(L, -1, getParentKey()); // Stack: mt, nifb, mt, parent mt | nil
-        if (lua_isnil(L, -1)) // Stack: mt, nifb, mt
+        lua_rawgetp(L, -2, getParentKey()); // Stack: mt, nifb, mt, ct, parent mt (pmt) | nil
+        if (lua_isnil(L, -1)) // Stack: mt, nifb, mt, ct, nil
         {
-            lua_pop(L, 1); // Stack: mt, nifb, mt
+            lua_pop(L, 1); // Stack: mt, nifb, mt, ct
             break;
         }
 
-        LUABRIDGE_ASSERT(lua_istable(L, -1)); // Stack: mt, nifb, mt, parent mt
-        lua_remove(L, -2); // Stack: mt, nifb, parent mt
+        LUABRIDGE_ASSERT(lua_istable(L, -1)); // Stack: mt, nifb, mt, ct, pmt
+        lua_remove(L, -2); // Stack: mt, nifb, mt, pmt
+        lua_remove(L, -2); // Stack: mt, nifb, pmt
     }
 
-    lua_pop(L, 1); // Stack: mt, nifb
+    if (is_key_metamethod)
+    {
+        lua_remove(L, -2); // Stack: mt, nifb, ct
+    }
+    else
+    {
+        lua_pop(L, 2); // Stack: mt, nifb
+        lua_pushvalue(L, 1); // Stack: mt, nifb, arg1
+    }
+
+    lua_pushvalue(L, 2); // Stack: mt, nifb, arg1 | ct, arg2
+    lua_pushvalue(L, 3); // Stack: mt, nifb, arg1 | ct, arg2, arg3
+    lua_call(L, 3, 0); // Stack: mt
 
-    lua_remove(L, -2); // Stack: nifb
-    lua_pushvalue(L, 1); // Stack: nifb, arg1
-    lua_pushvalue(L, 2); // Stack: nifb, arg1, arg2
-    lua_pushvalue(L, 3); // Stack: nifb, arg1, arg2, arg3
-    lua_call(L, 3, 0); // Stack: -
     return 0;
 }
 
@@ -382,11 +407,7 @@ inline int newindex_metamethod(lua_State* L, bool pushSelf)
         // Try in the property set table
         lua_rawgetp(L, -1, getPropsetKey()); // Stack: mt, propset table (ps) | nil
         if (lua_isnil(L, -1)) // Stack: mt, nil
-        {
-            lua_pop(L, 2); // Stack: -
             luaL_error(L, "no member named '%s'", key);
-            return 0;
-        }
 
         LUABRIDGE_ASSERT(lua_istable(L, -1));
 
@@ -414,11 +435,7 @@ inline int newindex_metamethod(lua_State* L, bool pushSelf)
         // Try in the parent
         lua_rawgetp(L, -1, getParentKey()); // Stack: mt, parent mt | nil
         if (lua_isnil(L, -1)) // Stack: mt, nil
-        {
-            lua_pop(L, 2); // Stack: -
             luaL_error(L, "no writable member '%s'", key);
-            return 0;
-        }
 
         LUABRIDGE_ASSERT(lua_istable(L, -1)); // Stack: mt, parent mt
         lua_remove(L, -2); // Stack: parent mt
@@ -510,7 +527,7 @@ inline int newindex_extended_class(lua_State* L)
 template <class C>
 static int tostring_metamethod(lua_State* L)
 {
-    const void* ptr = lua_topointer(L, -1);
+    const void* ptr = lua_topointer(L, 1);
 
     lua_getmetatable(L, -1); // Stack: metatable (mt)
     lua_rawgetp(L, -1, getTypeKey()); // Stack: mt, classname (cn)
@@ -1003,8 +1020,7 @@ inline int try_overload_functions(lua_State* L)
         if (err == LUABRIDGE_LUA_OK)
         {
             // calculate number of return values and return
-            const int nresults = lua_gettop(L) - nargs - 4; // 4: overloads, errors, key, table
-            return nresults;
+            return lua_gettop(L) - nargs - 4; // 4: overloads, errors, key, table
         }
         else if (err == LUA_ERRRUN)
         {

Source/LuaBridge/detail/Namespace.h

@@ -384,6 +384,8 @@ class Namespace : public detail::Registrar
             lua_pushcfunction_x(L, &detail::gc_metamethod<T>); // Stack: ns, co, cl, function
             rawsetfield(L, -2, "__gc"); // cl ["__gc"] = function. Stack: ns, co, cl
 #endif
+            lua_pushcfunction_x(L, &detail::tostring_metamethod<T>);
+            rawsetfield(L, -2, "__tostring");
             ++m_stackSize;
 
             createStaticTable(name, options); // Stack: ns, co, cl, st

Tests/CMakeLists.txt

@@ -14,6 +14,7 @@ add_subdirectory(${LUABRIDGE_RAVI_LOCATION} ravi)
 set (LUABRIDGE_TEST_SOURCE_FILES
   Source/AmalgamateTests.cpp
   Source/ArrayTests.cpp
+  Source/ClassExtensibleTests.cpp
   Source/ClassTests.cpp
   Source/CoroutineTests.cpp
   Source/EnumTests.cpp