Method basic_reference

3rd_party/lua_sol2/include/sol.hpp:6779–6783

	protected:
		basic_reference(lua_State* L, detail::global_tag) noexcept
		: luastate(detail::pick_main_thread<main_only>(L, L)) {
			lua_pushglobaltable(lua_state());
			ref = luaL_ref(lua_state(), LUA_REGISTRYINDEX);
		}

		int stack_index() const noexcept {
			return -1;