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How do I extend a class successfully?

Asked by

NotInventedHere 158

8 years ago

Hello, I am trying to figure out OOP in Roblox Lua.

What I have here is a "class" named BrickModel which can spawn bricks, and a "class" named UnanchoredBrickModel which can spawn bricks differently.

01local BrickModel = {}
02BrickModel.__index = BrickModel
03 
04function BrickModel:new(color, size)
05    local mt = setmetatable({color = color, size = size}, BrickModel)
06    mt.__index = self
07    return mt
08end
09 
10function BrickModel:createInstance(positionVector3) 
11 
12    -- code for creating a new part and returning it
13 
14end
15 
16local UnanchoredBrickModel = {}
17UnanchoredBrickModel.__index = UnanchoredBrickModel
18 
19function UnanchoredBrickModel:new(color, size)
20    local mt = setmetatable({color = color, size = size}, UnanchoredBrickModel)
21    mt.__index = self
22    return mt
23end
24 
25-- There is also a separate createInstance method for UnanchoredBrickModel, this has been skipped as it is self-explanatory
 View all 25 lines...

Ideally I would like UnanchoredBrickModel to just extend BrickModel. I have tried doing this by doing something like this:

`1`	`local` `UnanchoredBrickModel` `=` `BrickModel:new()`

However, when I called UnanchoredBrickModel:createInstance(), it seemed to call BrickModel:createInstance() instead. My friend suggested separating the two classes, although I would like to know if it would be possible to extend BrickModel to UnanchoredBrickModel, and if so, how.

1 answer

Answered by

pericuIosa 32

8 years ago

Edited 8 years ago

Don't quote me on any of this - I'm still getting the hang of OOP and metatables myself, but hopefully I can be of some use.

01--> declare the 'base' class.
02local Brick = {}
03Brick.__index = Brick
04 
05--> create the constructor for the 'base' class.
06function Brick.new(color, size)
07    local self = setmetatable({}, Brick)
08 
09    self.__index = self
10    self.color = color
11    self.size = size
12 
13    return self
14end
15 
16--> define methods for the 'base' class.
17function Brick:GetData()
18    print(self.color, self.size)
19end
20 
21--> declare the 'derived' class inheriting the 'base' class.
22local TransparentBrick = Brick.new()
23 
24--> create the constructor for the 'derived' class.
25function TransparentBrick.new(color, size, transparency)
26    local self = setmetatable(Brick.new(color, size), TransparentBrick)
27 
28    self.__index = self
29    self.transparency = transparency
30 
31    return self
32end
33 
34--> define methods for the 'derived' class.
35function TransparentBrick:GetData()
36    print(self.color, self.size, self.transparency)
37end
38 
39local brick = Brick.new('Deep orange', Vector3.new(1, 1, 1))
40brick:GetData()
41 
42local transparentBrick = TransparentBrick.new('Lavender', Vector3.new(2, 2, 2), 0.5)
43transparentBrick:GetData()
 View all 43 lines...

How do I extend a class successfully?

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