# sol2 3.5.0 documentation

## metatable_key

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# 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}