Make Lua type checks optional. They add a lot of overhead to Lua dispatches.

stepmania/src/LuaBinding.cpp

@@ -2,6 +2,12 @@
 #include "LuaBinding.h"
 #include "RageUtil.h"
 
+// If defined, type checks for functions will be skipped.  These add
+// up and can become expensive (performed for every function dispatch),
+// but without them it's possible to call functions on incompatible
+// types (eg. "Actor.x(GAMESTATE, 10)"), which will crash or cause corruption.
+// #define FAST_LUA
+
 void CreateMethodsTable( lua_State *L, const CString &sName )
 {
 	lua_pushlstring( L, sName.data(), sName.size() );
@@ -20,8 +26,13 @@ void CreateMethodsTable( lua_State *L, const CString &sName )
  * Get a userdata, and check that it's either szType or a type
  * derived from szType, by walking the __index chain.
  */
-bool CheckLuaObjectType( lua_State *L, int narg, const char *szType )
+bool CheckLuaObjectType( lua_State *L, int narg, const char *szType, bool bOptional )
 {
+#if defined(FAST_LUA)
+	if( bOptional )
+		return true;
+#endif
+
 	ASSERT_M( narg > 0, ssprintf("%i", narg) ); // negative offsets not supported
 
 	int iTop = lua_gettop(L);

stepmania/src/LuaBinding.h

@@ -7,7 +7,7 @@
 class LuaReference;
 
 void CreateMethodsTable( lua_State *L, const CString &szName );
-bool CheckLuaObjectType( lua_State *L, int narg, const char *szType );
+bool CheckLuaObjectType( lua_State *L, int narg, const char *szType, bool bOptional=false );
 void *GetUserdataFromGlobalTable( Lua *L, const char *szType, int iArg );
 void ApplyDerivedType( Lua *L, const CString &sClassname, void *pSelf );
 
@@ -96,7 +96,7 @@ public:
 	// Get userdata from the Lua stack and return a pointer to T object.
 	static T *check( lua_State *L, int narg, bool bIsSelf = false )
 	{
-		if( !CheckLuaObjectType(L, narg, m_sClassName) )
+		if( !CheckLuaObjectType(L, narg, m_sClassName, true) )
 		{
 			if( bIsSelf )
 				luaL_typerror( L, narg, m_sClassName );