Add default __eq implementation

* Renamed SWIG_Lua_equal to SWIG_Lua_class_equal
* If class has no __eq implemented, then default __eq is provided.
  Default __eq compares actual pointers stored inside Lua userdata

Examples/test-suite/lua/cpp_basic_runme.lua

@@ -86,3 +86,14 @@ f4_name = tostring(f4)
 assert( f2_name == "Foo" )
 assert( f3_name == "Foo" )
 assert( f4_name == "FooSubSub" )
+
+-- Test __eq implementation supplied by default
+
+-- eq_f1 and eq_f2 must be different userdata with same Foo* pointer. If eq_f1 and eq_f2 are the same userdata (e.g.)
+-- > eq_f1 = smth
+-- > eq_f2 = eq_f1
+-- then default Lua equality comparison kicks in and considers them equal. Access to global_fptr is actually a
+-- function call (internally) and it returns new userdata each time.
+eq_f1 = cb.Bar.global_fptr
+eq_f2 = cb.Bar.global_fptr
+assert( eq_f1 == eq_f2 )

Lib/lua/luarun.swg

@@ -1037,6 +1037,23 @@ SWIGINTERN int  SWIG_Lua_class_disown(lua_State *L)
   return 0;
 }
 
+/* lua callable function to compare userdata's value
+the issue is that two userdata may point to the same thing
+but to lua, they are different objects */
+SWIGRUNTIME int SWIG_Lua_class_equal(lua_State *L)
+{
+  int result;
+  swig_lua_userdata *usr1,*usr2;
+  if (!lua_isuserdata(L,1) || !lua_isuserdata(L,2))  /* just in case */
+    return 0;  /* nil reply */
+  usr1=(swig_lua_userdata*)lua_touserdata(L,1);  /* get data */
+  usr2=(swig_lua_userdata*)lua_touserdata(L,2);  /* get data */
+  /*result=(usr1->ptr==usr2->ptr && usr1->type==usr2->type); only works if type is the same*/
+  result=(usr1->ptr==usr2->ptr);
+   lua_pushboolean(L,result);
+  return 1;
+}
+
 /* populate table at the top of the stack with metamethods that ought to be inherited */
 SWIGINTERN void SWIG_Lua_populate_inheritable_metamethods(lua_State *L)
 {
@@ -1471,6 +1488,18 @@ SWIGINTERN void SWIG_Lua_add_class_user_metamethods(lua_State *L, swig_lua_class
     lua_pop(L,1); /* remove copy of the key */
   }
 
+  /* Special handling for __eq method */
+  lua_pushstring(L, "__eq");
+  lua_pushvalue(L,-1);
+  lua_rawget(L,metatable_index);
+  const int eq_undefined = lua_isnil(L,-1);
+  lua_pop(L,1);
+  if( eq_undefined ) {
+    lua_pushcfunction(L, SWIG_Lua_class_equal);
+    lua_rawset(L, metatable_index);
+  } else {
+    lua_pop(L,1); /* remove copy of the key */
+  }
   /* Warning: __index and __newindex are SWIG-defined. For user-defined operator[]
    * a __getitem/__setitem method should be defined
    */
@@ -1788,23 +1817,6 @@ SWIGRUNTIME int SWIG_Lua_type(lua_State *L)
   return 1;
 }
 
-/* lua callable function to compare userdata's value
-the issue is that two userdata may point to the same thing
-but to lua, they are different objects */
-SWIGRUNTIME int SWIG_Lua_equal(lua_State *L)
-{
-  int result;
-  swig_lua_userdata *usr1,*usr2;
-  if (!lua_isuserdata(L,1) || !lua_isuserdata(L,2))  /* just in case */
-    return 0;  /* nil reply */
-  usr1=(swig_lua_userdata*)lua_touserdata(L,1);  /* get data */
-  usr2=(swig_lua_userdata*)lua_touserdata(L,2);  /* get data */
-  /*result=(usr1->ptr==usr2->ptr && usr1->type==usr2->type); only works if type is the same*/
-  result=(usr1->ptr==usr2->ptr);
-   lua_pushboolean(L,result);
-  return 1;
-}
-
 /* -----------------------------------------------------------------------------
  * global variable support code: class/struct typemap functions
  * ----------------------------------------------------------------------------- */

Lib/lua/luaruntime.swg

@@ -40,7 +40,7 @@ SWIGEXPORT int SWIG_init(lua_State* L) /* default Lua action */
 #if ((SWIG_LUA_TARGET != SWIG_LUA_FLAVOR_ELUA) && (SWIG_LUA_TARGET != SWIG_LUA_FLAVOR_ELUAC)) || defined(SWIG_LUA_ELUA_EMULATE)
   /* add a global fn */
   SWIG_Lua_add_function(L,"swig_type",SWIG_Lua_type);
-  SWIG_Lua_add_function(L,"swig_equals",SWIG_Lua_equal);
+  SWIG_Lua_add_function(L,"swig_equals",SWIG_Lua_class_equal);
 #endif
 
 #if (SWIG_LUA_TARGET != SWIG_LUA_FLAVOR_ELUAC)