Object Oriented Problem

[jimbobert94]

So I want to use an attribute in the same object/table that the caller is in. i.e.:

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function create_player(self,filename,x,y)
    self = { 
        placement = { 
            x     = x,
            y     = y 
        },  
        image      = { 
            body   = love.graphics.newImage(filename),
            width  = body:getWidth(),
            height = body:getHeight()
        },

The rest of the function is irrelevant. Anyway, when I run the code, an error pops up saying that body is a nil value. So my problem lies there. I've tried

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width = self.image.body:getWidth()

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width = image.body:getWidth()

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width = self.body:getWidth()

So which one is it?

[Santos]

The reason why width = body:getWidth() isn't working is because it's looking for a variable named body, which isn't actually there.

width = self.image.body:getWidth() seems like it should work, however if you're trying to access this within the definition of the self table, self doesn't exist yet. After self has been created though, this will work!

Code: Select all

function create_player(self,filename,x,y)
	self = {
		placement = {
			x     = x,
			y     = y
		},
		image      = {
			body   = love.graphics.newImage(filename)
		}
	}

	self.image.width = self.image.body:getWidth()
	self.image.height = self.image.body:getHeight()

[jimbobert94]

The reason why width = body:getWidth() isn't working is because it's looking for a variable named body, which isn't actually there.

width = self.image.body:getWidth() seems like it should work, however if you're trying to access this within the definition of the self table, self doesn't exist yet. After self has been created though, this will work!

Code: Select all

function create_player(self,filename,x,y)
	self = {
		placement = {
			x     = x,
			y     = y
		},
		image      = {
			body   = love.graphics.newImage(filename)
		}
	}

	self.image.width = self.image.body:getWidth()
	self.image.height = self.image.body:getHeight()

I thought that might be it. Nice alternative, Thanks a lot. If I can upvote you, I will. Let me check.

[Inny]

You probably don't want to abuse the variable "self" like that, since you'll end up heavily shadowing it with other object-oriented code.

Instead, define your player class like so:

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Player = {}
Player.__index = Player
function Player.new(filename,x,y)
  local self = {
    placement = {
      x = x,
      y = y
    },
    image = {
      body = love.graphics.newImage(filename)
    }
  }
  self.image.width = self.image.body:getWidth()
  self.image.height = self.image.body:getHeight()
  return setmetatable(self, Player)
end

function Player:doSomething()
  -- example of defining a class function for the objects to use
end

player = Player.new("player.png", 0, 0)
player:doSomething()

The important parts of this are: self is local to the function, not global. Player, with a capital P, is that table where you can define functions for the player object. player, with a lowercase p, is the global object that you'll interact with.

This is the bare minimum basic class system for lua, which doesn't require a framework, and should cover most of your needs.

Also, I recommend this to everyone, please read the free ebook Programming Lua.

[jimbobert94]

You probably don't want to abuse the variable "self" like that, since you'll end up heavily shadowing it with other object-oriented code.

Instead, define your player class like so:

Code: Select all

Player = {}
Player.__index = Player
function Player.new(filename,x,y)
  local self = {
    placement = {
      x = x,
      y = y
    },
    image = {
      body = love.graphics.newImage(filename)
    }
  }
  self.image.width = self.image.body:getWidth()
  self.image.height = self.image.body:getHeight()
  return setmetatable(self, Player)
end

function Player:doSomething()
  -- example of defining a class function for the objects to use
end

player = Player.new("player.png", 0, 0)
player:doSomething()

The important parts of this are: self is local to the function, not global. Player, with a capital P, is that table where you can define functions for the player object. player, with a lowercase p, is the global object that you'll interact with.

This is the bare minimum basic class system for lua, which doesn't require a framework, and should cover most of your needs.

Also, I recommend this to everyone, please read the free ebook Programming Lua.

Yeah, I got that after running the code, but thanks for the additional help.

[jimbobert94]

There should totally be a upvote/downvote system here by the way.

[Nixola]

There was the Karma mod, but a phpBB update broke it