How to return C++ object to lua?
My C++ code is following:
class MyClass
{
public:
void say()
{
print("Hello\r\n");
}
};
int test(lua_State* l)
{
MyClass* obj = new MyClass();
lua_pushlightuserdata(l, obj);
return 1;
}
Lua Test is following:
local a = MyClass:new()
a:say() <--- OK, beacause I set metatable!!
local b = test()
b:say() <--- ERROR: attempt to index local 'b' (a userdata value)
How to modify test() function to work fine?
obj will auto destory by lua ?
PS: I has set MyClass metatable is following
void l_registerClass()
{
lua_newtable(l);
int methods = lua_gettop(l);
luaL_newmetatable(l, "MyClass");
int metatable = lua_gettop(l);
lua_pushvalue(l, methods);
lua_setglobal(l, "MyClass");
lua_pushvalue(l, methods);
l_set(l, metatable, "__metatable");
//set metatable __index
lua_pushvalue(l, methods);
l_set(l, metatable, "__index");
//set metatable __gc
lua_pushcfunction(l, l_destructor);
l_set(l, metatable, "__gc");
//set method table
lua_newtable(l); // mt for method table
lua_pushcfunction(l, l_constructor);
lua_pushvalue(l, -1); // dup new_T function
l_set(l, methods, "new"); // add new_T to method table
l_set(l, -3, "__call"); // mt.__call = new_T
lua_setmetatable(l, methods);
// set methods metatable
lua_pushstring(l, "say");
lua_pushcclosure(l, l_proxy, 1);
lua_settable(l, methods);
lua_pop(l, 2);
}
int l_proxy(lua_State* l)
{
int i = (int)lua_tonumber(l, lua_upvalueindex(1));
lua_remove(l, 1); // remove self so member function args start at index 1
//call real function
MyClass* obj = getInstance();
obj->say();
return 1;
}
I should don't lost step ?
I don't use any Lua Binding Framework, I am using pure Lua Library.
==== update 1 ====
Thanks for user1520427's answer, but....
int test(lua_State* l)
{
MyClass** c = (MyClass**)lua_newuserdata(l, sizeof(MyClass*));
*c = new MyClass(); // we manage this
lua_getglobal(l, "MyClass");
lua_setmetatable(l, -2);
return 1;
}
and I test it in Lua
local b = test()
print( type(b) )
local meta = getmetatable(b)
for k,v in pairs(meta) do
print(" ", k, v)
end
Lua show metatable is correct.
userdata
say function: 00602860
new function: 00493665
But lua still shows the same error in
b:say() <-- attempt to index local 'b' (a userdata value)
=== update 2 ===
int test(lua_State* l)
{
MyClass** c = (MyClass**)lua_newuserdata(l, sizeof(MyClass*));
*c = new MyClass(); // we manage this
luaL_getmetatable(l, "MyClass"); //
lua_getglobal(l, "MyClass");
lua_setmetatable(l, -2);
return 1;
}
the lua test result:
b:say() <-- attempt to call method 'say' (a nil value)
=== update 3 ===
int test(lua_State* l)
{
MyClass** c = (MyClass**)lua_newuserdata(l, sizeof(MyClass*));
*c = new MyClass(); // we manage this
luaL_getmetatable(l, "MyClass");
luaL_setmetatable(l, "MyClass"); //modify
return 1;
}
Lua test result:
b:say() <-- calling 'say' on bad self
thanks for user1520427 and lhf
correct code sould is following:
Lua test code is work fine.