Create properties and methods Lua C++

Question

This is rather tricky to explain and I could not find anything on this in the documentation or anywhere on the net so I thought this would be a suitable place for this question.

I'm trying to register properties and methods on an object in Lua using C++.

This is what I'm trying to achieve in Lua:

player = createPlayer()
player:jump() // method
player.x = player.x + 3 // properties

I can easily achieve the first line in the example using C++

int create_player(lua_State *L)
{
    Player* player = new Player();
    ..

    return 0;
}

int main(int args, char * argv[])
{
    lua_State* L = lua_open();
    luaL_openlibs(L);    

    lua_register(L, "createPlayer", create_player);

    luaL_dofile(L, "main.lua");

    ..
    return 0;
}

But how do I create the method :jump() and properties .setX and .getX for createPlayer?

Answer 1

What you could have searched is "Binding C++ to Lua".

Since it's a rather popular question, I'll post an answer with a project compilable online:

Starting from a C++ class:

class Player {
  int x;
public:
  Player() : x(0) {}
  int get_x() const { return x; }
  void set_x(int x_) { x = x_; }
  void jump() {}
};

You can then create bindings using LuaBridge without writing the boilerplate for each of the bound members yourself:

void luabridge_bind(lua_State *L) {
 luabridge::getGlobalNamespace(L)
 .beginClass<Player>("Player")
  .addConstructor<void (*)(), RefCountedPtr<Player> /* shared c++/lua lifetime */ >()
  .addProperty("x", &Player::get_x, &Player::set_x)
  .addFunction("jump", &Player::jump)
 .endClass()
 ; 
}

Using a dedicated Lua State wrapper LuaState, you can then open a Lua state and perform the bindings:

lua::State state;
luabridge_bind(state.getState());

Running the script using some trace output:

try {
  static const char *test =
  "player = Player() \n"
  "player:jump() \n"
  "player.x = player.x + 3"
  ;
  state.doString(test);
}
catch (std::exception &e) {
  std::cerr << e.what() << std::endl;
}

Produces the following output:

Player
jump
get_x
set_x 3
~Player

You can see the whole thing live at Travis-CI