Re: Inheriting from a userdata object

[Stephen Virgo <melonrock@...>]

> Excellent, this worked and is in fact a much more full solution than I need

In actual fact it didn't quite work when I tried it fully in the wild,
my apologies. I was able to re-arrange your solution to the following
however, which fulfills my needs:-



game_wrapper = {
	this_bool = false,
	that_bool = true,
	some_value = 7
};


-- allow game_wrapper to inherit from game
function game_wrapper:__index(key)
 	local field = rawget(getmetatable(self), key);
	local retval = nil;
	
	if type(field) == "nil" then
		-- key doesn't exist in self, look for it in the prototype object
		local proto = rawget(self, "game");
		field = proto and proto[key];
				
		if type(field) == "function" then
			-- key exists as a function on the prototype object
			retval = function(obj, ...)
				return field(proto, ...);
			end;
		else
			-- return whatever this key refers to on the prototype object
			retval = field;
		end;
	else
		-- key exists in self
		if type(field) == "function" then
			-- key exists as a function on the self object
			retval = function(obj, ...)
				return field(self, ...);
			end;
		else
			-- return whatever this key refers to on the self object
			retval = field;
		end;
	end;
	
	return retval;
end;


function game_wrapper:some_function()
	return self.some_value;
end;


function game_wrapper:quit()
	self:out("A call to game:quit() would usually end the game, but it
won't now that it's overridden!");
end;


function game_wrapper:new(new_game)
	gw = {
		game = new_game
	};
	
	setmetatable(gw, game_wrapper);

	return gw;
end;



my_game = game_wrapper:new(game);

my_game:out("This prints as if I'd used game:out!");
my_game:out("my_game.that_bool is " .. tostring(my_game.that_bool));
my_game:out("my_game:some_function() returns " ..
tostring(my_game:some_function()));
my_game:quit();


--[[ Output would be..

This prints as if I'd used game:out!
my_game.that_bool is true
my_game:some_function() returns 7
A call to game:quit() would usually end the game, but it won't now
that it's overridden!

]]