Inheritance: adding parameters to a child class not in the parent class

MoKaLux · December 2021

hope you are all doing fine

I have a problem

~~I want to inherit from classes but that doesn't work for me, could you please have a look?~~
I would like to add parameters to a class that inherits another class but that doesn't work for me, could you please have a look?

I have the base class:

Tiled_Shape_Polygon = Core.class(Sprite)
 
function Tiled_Shape_Polygon:init(xworld, xparams, xlevelscale)
	-- params
	local params = xparams or {}
	params.x = xparams.x or 0
	params.y = xparams.y or 0
	...
	self.x = params.x
	self.y = params.y
end

Then I inherit it from this class:

--!NEEDS:../../tiled/tiled_polygon.lua
Collectibles = Core.class(Tiled_Shape_Polygon)
 
function Collectibles:init()
	self.x += 10 -- this works fine
	self.y += 10 -- this works fine
	...
end

So far so good, but I would like to add additional arguments to the Collectibles class, how can I do?

I tried:

function Collectibles:init(xparams2)
	local params2 = xparams2 or {} -- xparams2 will be a table adding extra stuff to collectibles
	...
end

and this: (because child expects same arguments as parent as seen in an old post from ar2rsawseen here https://forum.gideros.rocks/discussion/comment/22775/#Comment_22775)

function Tiled_Shape_Polygon:init(xworld, xparams, xlevelscale, xparams2)
	-- params
	local params = xparams or {}
	local params2 = xparams2 or {}
	...
end
 
function Collectibles:init(xworld, xparams, xlevelscale, xparams2)
	local params2 = xparams2 or {} -- xparams2 will be a table adding extra stuff to collectibles
	...
end

...

But every time I have this error: attempt to index local 'xparams2' (a nil value)

How can I add extra parameters to Collectibles init without adding them to the parent class? Is it possible?

Thank you in advance for your help

MoKaLux · December 2021

So there are different workarounds:
1) check inside particle2D:init which arguments have been passed, so you could determine who is calling constructor and what to do
2) in particle2D leave the init without argumetns and create antoher method like particle2D:create(texRegion, ID) which you could call from blob:init
3) Do not inherit from particle2D but make the instance of it inside blob:init and store as a property so you could use it for anything you wanted to use it

In the first post I believe I tried solution 1) which didn't work for me

So solution 2) looks good enough

Viva Gideros

rrraptor · December 2021

@MoKaLux

Foo = Core.class(Sprite)
function Foo:init(baz)
	self.baz = baz or 1024
end
 
Bar = Core.class(Foo, function(baz, delta) 
	return baz or 2048 
end)
 
function Bar:init(baz, delta)
	self.delta = delta or 0.001
end
 
foo = Foo.new()
print(foo.baz)
bar = Bar.new()
print(bar.baz, bar.delta)
bar = Bar.new(512, 0.1)
print(bar.baz, bar.delta)

Outputs:
1024
2048 0.001
512 0.1

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