sol2/examples/source/customization_multiple.cpp

#define SOL_ALL_SAFETIES_ON 1
#include <sol/sol.hpp>

#include <iostream>

struct two_things {
	int a;
	bool b;
};

template <typename Handler>
bool sol_lua_check(sol::types<two_things>, lua_State* L,
     int index, Handler&& handler,
     sol::stack::record& tracking) {
	// indices can be negative to count backwards from the top
	// of the stack, rather than the bottom up to deal with
	// this, we adjust the index to its absolute position using
	// the lua_absindex function
	int absolute_index = lua_absindex(L, index);
	// Check first and second second index for being the proper
	// types
	bool success
	     = sol::stack::check<int>(L, absolute_index, handler)
	     && sol::stack::check<bool>(
	          L, absolute_index + 1, handler);
	tracking.use(2);
	return success;
}

two_things sol_lua_get(sol::types<two_things>, lua_State* L,
     int index, sol::stack::record& tracking) {
	int absolute_index = lua_absindex(L, index);
	// Get the first element
	int a = sol::stack::get<int>(L, absolute_index);
	// Get the second element,
	// in the +1 position from the first
	bool b = sol::stack::get<bool>(L, absolute_index + 1);
	// we use 2 slots, each of the previous takes 1
	tracking.use(2);
	return two_things { a, b };
}

int sol_lua_push(lua_State* L, const two_things& things) {
	int amount = sol::stack::push(L, things.a);
	// amount will be 1: int pushes 1 item
	amount += sol::stack::push(L, things.b);
	// amount 2 now, since bool pushes a single item
	// Return 2 things
	return amount;
}

int main() {
	std::cout << "=== customization ===" << std::endl;
	std::cout << std::boolalpha;

	sol::state lua;
	lua.open_libraries(sol::lib::base);

	// Create a pass-through style of function
	lua.script(
	     "function f ( a, b ) print(a, b) return a, b end");

	// get the function out of Lua
	sol::function f = lua["f"];

	two_things things = f(two_things { 24, false });
	SOL_ASSERT(things.a == 24);
	SOL_ASSERT(things.b == false);
	// things.a == 24
	// things.b == true

	std::cout << "things.a: " << things.a << std::endl;
	std::cout << "things.b: " << things.b << std::endl;
	std::cout << std::endl;

	return 0;
}