metatable_key¶
a key for setting and getting an object’s metatable
struct metatable_key_t {};
const metatable_key_t metatable_key;
You can use this in conjunction with sol::table to set/get a metatable. Lua metatables are powerful ways to override default behavior of objects for various kinds of operators, among other things. Here is an entirely complete example, showing getting and working with a usertype’s metatable defined by sol:
messing with metatables¶
1#define SOL_ALL_SAFETIES_ON 1
2#include <sol/sol.hpp>
3
4
5int main(int, char*[]) {
6
7 struct bark {
8 int operator()(int x) {
9 return x;
10 }
11 };
12
13 sol::state lua;
14 lua.open_libraries(sol::lib::base);
15
16 lua.new_usertype<bark>("bark",
17 sol::meta_function::call_function,
18 &bark::operator());
19
20 bark b;
21 lua.set("b", &b);
22
23 sol::table b_as_table = lua["b"];
24 sol::table b_metatable = b_as_table[sol::metatable_key];
25 sol::function b_call = b_metatable["__call"];
26 sol::function b_as_function = lua["b"];
27
28 int result1 = b_as_function(1);
29 // pass 'self' directly to argument
30 int result2 = b_call(b, 1);
31 SOL_ASSERT(result1 == result2);
32 SOL_ASSERT(result1 == 1);
33 SOL_ASSERT(result2 == 1);
34}