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How do I extend a class successfully?

Asked by

NotInventedHere 158

7 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.


local BrickModel = {}
BrickModel.__index = BrickModel

function BrickModel:new(color, size)
    local mt = setmetatable({color = color, size = size}, BrickModel)
    mt.__index = self
    return mt
end

function BrickModel:createInstance(positionVector3) 

    -- code for creating a new part and returning it

end

local UnanchoredBrickModel = {}
UnanchoredBrickModel.__index = UnanchoredBrickModel

function UnanchoredBrickModel:new(color, size)
    local mt = setmetatable({color = color, size = size}, UnanchoredBrickModel)
    mt.__index = self
    return mt
end

-- There is also a separate createInstance method for UnanchoredBrickModel, this has been skipped as it is self-explanatory

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

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

7 years ago

Edited 7 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.

--> declare the 'base' class.
local Brick = {}
Brick.__index = Brick

--> create the constructor for the 'base' class.
function Brick.new(color, size)
    local self = setmetatable({}, Brick)

    self.__index = self
    self.color = color
    self.size = size

    return self
end

--> define methods for the 'base' class.
function Brick:GetData()
    print(self.color, self.size)
end

--> declare the 'derived' class inheriting the 'base' class.
local TransparentBrick = Brick.new()

--> create the constructor for the 'derived' class.
function TransparentBrick.new(color, size, transparency)
    local self = setmetatable(Brick.new(color, size), TransparentBrick)

    self.__index = self
    self.transparency = transparency

    return self
end

--> define methods for the 'derived' class.
function TransparentBrick:GetData()
    print(self.color, self.size, self.transparency)
end

local brick = Brick.new('Deep orange', Vector3.new(1, 1, 1))
brick:GetData()

local transparentBrick = TransparentBrick.new('Lavender', Vector3.new(2, 2, 2), 0.5)
transparentBrick:GetData()

How do I extend a class successfully?

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