有没有办法将 Lua 成员变量绑定为对该变量名称的 C/C++ 函数的调用

Question

I'm totally new to Lua. From what I understand it is possible to bind Lua variables and methods to ones on the C/C++ side.

But is it possible to bind a user type variable to the call of the C/C++ function which may look like properties on the Lua side ?

Example:

// C++
struct player {
  int get_value(const std::string& property) const {
    auto it = values.find(name);

    if (it != values.end()) {
      return it->second;
    }

    return -1;
  }

  std::map<std::string, int> values;
};

And on the Lua side:

-- Lua
p = player.new()
print(p.score)

So when I call p.score in Lua, it gets translated to the call to the player::get_value function on C++ side with the value of property "score" ?

SOLUTION

Thanks to @Vlad for the directions!

I came up using sol2 which is in my opinion a very nice C++ library binding to Lua!

Here is how it can be done with sol2:

struct Player {
  sol::object get(const std::string& key, sol::this_state state) {
    const auto& it = values.find(key);

    if (it != values.cend()) {
      return sol::make_object(state, it->second);
    }

    return sol::lua_nil;
  }

  std::map<std::string, int> values;
};

int main() {
  Player player;

  player.values.emplace("score", 123);

  sol::state lua;

  lua.open_libraries(sol::lib::base);
  lua.new_usertype<Player>("Player", sol::meta_function::index, &Player::get);
  lua.set("player", &player);

  lua.script(R"(
    print("Player score: ", player.score)
  )");
  return 0;
}

Console output

Player score:   123

Answer 1

The object player should have metatable set with fields __index / __newindex set to C function that will be called when Lua is trying to read or write the field that doesn't exist in the Lua object.

Normally the Lua object representing the native object ( player in your case) will be a userdata , either storing the pointer to the C++ object, or hosting it within its storage.

The metamethods __index / __newindex will receive in arguments the reference to the object being queried, the key value (eg your score field), and the value to store in case of __newindex metamethod. So you can find your native object and desired property easily.

Some people prefer using existing binding solutions - tolua++/sol/luabind/etc, but it's very simple to implement required functionality yourself.