Safe_handle.cpp

#include <sol.hpp>
#include <string>
#include <iostream>

class Entity {
public:
    Entity() : name("John") {}
    const std::string& getName() const { return name; }
private:
    std::string name;
};

int main()
{
    sol::state lua;
    lua.open_libraries();

    lua.new_usertype<Entity>("Entity",
        "getName", &Entity::getName,
        "extraFunc", [](Entity& e) { std::cout << "EXTRA!" << e.getName() << " is working\n"; });

    lua.do_file("script.lua");

    sol::function createHandle = lua["createHandle"];
    sol::function test = lua["test"];
    sol::function test2 = lua["test2"];
    sol::function onEntityDeleted = lua["onEntityDeleted"];

    sol::object handle(lua);

    {
        Entity e;
        handle = createHandle(e);

        test(handle); // everything ok here
        test2(e);

        // entity will be destroyed after leaving the scope, so we need to notify handle about that
        onEntityDeleted(handle);
    }

    try {
        test(handle); // this will throw error
    }
    catch (sol::error& e) {
        std::cout << e.what() << std::endl;
    }
    return 0;
}