Lua 5.2 Sandbox, alternate answer to: https://stackoverflow.com/questions/63643025/lua-5-2-sandboxing-in-different-objects-with-c-api

gistfile1.cpp

// Alternate answer to: https://stackoverflow.com/questions/63643025/lua-5-2-sandboxing-in-different-objects-with-c-api

#include <string>
#include <cassert>
#include <iostream>

#include <lua/lua.hpp>

#include <fmt/format.h>

class AwesomeThing
{
    lua_State* _lua;
    std::string _name;

public:
    AwesomeThing(lua_State* L, const std::string& name, const std::string& luafile)
        : _lua{ L },
          _name{ name }
    {
        assert(luaL_loadfile(_lua, luafile.c_str()) == 0); // 1:chunk

        const std::string code = _name + " = setmetatable({}, {__index = _G})";
        luaL_dostring(_lua, code.c_str()); 
        lua_getglobal(L, _name.c_str()); //1:chunk, 2:mt

        lua_setupvalue(_lua, 1, 1); // 1:chunk

        if (lua_pcall(_lua, 0, 0, 0) != 0) // 1:env
        {
            auto error = lua_tostring(_lua, -1);
            throw std::runtime_error(error);
        }

        lua_settop(_lua, 0);
    }

    void init()
    {
        // call onInit from Lua

        // first get the execution environment and set that
        lua_getglobal(_lua, _name.c_str()); // 1:env
        auto x = lua_typename(_lua, 1);
        std::cout << "x:" << x << '\n';
        //assert(lua_isnil(_lua, 1) == 0);
        //assert(lua_istable(_lua, 1) == 1);

        lua_getfield(_lua, 1, "onInit"); // 1:env, 2:func
        assert(lua_isnil(_lua, 2) == 0);
        assert(lua_isfunction(_lua, 2) == 1);

        assert(lua_pcall(_lua, 0, LUA_MULTRET, 0) == 0); // 1:env, 2:retval

        lua_settop(_lua, 0);
        //// manually clear the stack to make sure we're balanced
        //lua_pop(_lua, 1); // -1:env
        //lua_pop(_lua, 1); // empty stack
        //assert(lua_gettop(_lua) == 0);
    }
};

int main()
{
    lua_State* L = luaL_newstate();
    luaL_openlibs(L);

    AwesomeThing at1(L, "thing1", "file1.lua");
    AwesomeThing at2(L, "thing2", "file2.lua");

    at1.init();
    at2.init();

    return 0;
}