Inherit attributes

somezombiegm · March 2014

Hello, I want my "plane" class to inherit from my "vehicle" class, but I don't know how to add my vehicle attributes to the plane attributes.

I'm thinking the solution could be calling from "plane:init" the vehicle.init, but I don't know how to do it. In java you could call the superior constructor by using "this".

Please help. Here is my test code:

vehicle = gideros.class(Sprite)
 
function vehicle:init(name, speed, passengers)
	self.name = name
	self.speed = speed
	self.passengers = passengers
end
------------------------------------
plane = gideros.class(vehicle)
 
function plane:init(name, speed, passengers, height)
	self.height = height
        -- in here should I call the vehicle's init??
end
------------------------------------
vehicleTest = gideros.class(Sprite)
 
function vehicleTest:init()
	obj = plane.new("name", 100, 30, 3000)
	print(obj.height)
	print(obj.passengers)
end

ar2rsawseen · March 2014

the init of the parent class is called automatically, even before your classes init is called

meaning when function plane:init is called, all the name, speed, etc properties should already be set, because vehicle:init already did that

ar2rsawseen · March 2014

This way for example, you can extend native classes, like creating CenteredBitmap

 
CenteredBitmap = Core.class(Bitmap)
 
function CenteredBitmap:init(texture)
    self:setAnchorPoint(0.5, 0.5)
end
 
stage:addChild(CenteredBitmap.new(Texture.new("myimage.png", true)))

somezombiegm · March 2014

Ok, but how can I retrieve the passengers attribute? when I print

print(obj.passengers)

it returns me a nil value

ar2rsawseen · March 2014

Really?
I just tried your example and it works as expected, printing all the attributes

Which Gideros Version are you using?

somezombiegm · March 2014

Yeah, but it doesn't print it right either, it prints 30 rather than 3000.

I'm using Gideros v2014.01 for windows

ar2rsawseen · March 2014

So does it print nil or values?

Here is my test result, that works correctly for me

vehicle = gideros.class(Sprite)
 
function vehicle:init(name, speed, passengers)
 self.name = name
 self.speed = speed
 self.passengers = passengers
end
------------------------------------
plane = gideros.class(vehicle)
 
function plane:init(name, speed, passengers, height)
 self.height = height
end
------------------------------------
vehicleTest = gideros.class(Sprite)
 
function vehicleTest:init()
	obj = plane.new("name", 100, 30, 3000)
	print(obj.name, obj.speed, obj.passengers, obj.height)
	--prints name 100 30 3000
end
 
vehicleTest.new()

somezombiegm · March 2014

I edited the init on plane cause it needed and extra argument for the object I think. So I changed this:

function plane:init(name, speed, passengers, height)

to this:

function plane:init(newObj, name, speed, passengers, height)

However I can't retrieve the vehicle values, they print nil values. I don't even think they're being initialized correctly.

Let me test your last comment...

ar2rsawseen · March 2014

if you pass newObj as first argument and it is meant only for plane, then you have a problem, because first three arguments will be automatically used by vehicle class as name, speed and passengers

somezombiegm · March 2014

The newObj change I made was because I tried to create the object using ":" but I change it back again now.

So I tried your exact code and it prints

nil nil nil 3000

somezombiegm · March 2014

Wait, it works! But I added all the code to main.lua. I had each file separated on vehicle.lua, plane.lua and vehicleTest.lua. Sorry for not specifying.

But I would preffer doing it my way, cause my actual code is pretty large, that's just a test code. So, any thoughts why it doesn't work separating the files?

ar2rsawseen · March 2014

@somezombiegm ah I see
it makes sense now
click on the plain.lua in your project manager and select Code Dependencies
and there select vehicle.lua
So it would always load vehicle class before plain class

somezombiegm · March 2014

Yes! that fixed it! But I still don't understand why it works. Specially this part:

function vehicle:init(name, speed, passengers)
	self.name = name
	self.speed = speed
	self.passengers = passengers
end

I never call vehicle.new and send those 3 parameters. Does it know I am calling the plane class and gets the parameters in order of appearance automatically?

One more thing. I change the plane class parameters leaving only height and it still works:

function plane:init(height)
 self.height = height
end

Man I'm so confused

ar2rsawseen · March 2014

Basically it automatically passes to the parent class all the parameters you pass to the current class constructor (but only constructor, not other methods)

And it should not have worked with simply height
if you only accept height in plane, then height should have value "name"

somezombiegm · March 2014

It prints all the values when I put only height on "plane" though

ar2rsawseen · March 2014

@somezombiegm and correct values?
in you example self.height should be name.

Can you post a complete example for me to try

somezombiegm · March 2014

I'm sorry, I triple checked it and it does't work with only height on plane. The working code is:

vehicle.lua

vehicle = gideros.class(Sprite)
 
function vehicle:init(name, speed, passengers)
 self.name = name
 self.speed = speed
 self.passengers = passengers
end

plane.lua

plane = gideros.class(vehicle)
 
function plane:init(name, speed, passengers, height)
 self.height = height
end

vehicleTest.lua

vehicleTest = gideros.class(Sprite)
 
function vehicleTest:init()
	obj = plane.new("name", 100, 30, 3000)
	print(obj.name, obj.speed, obj.passengers, obj.height)
end
 
vehicleTest.new()

and it prints: name 100 30 3000

Thanks a lot for your help!

ar2rsawseen · March 2014

yes but here you have

function plane:init(name, speed, passengers, height)

somezombiegm · March 2014

Yeah, what I meant is that with

function plane:init(height)

doesn't work. I thought it did but I wasn't correctly checking the print. It printed name 100 30 name $:\$ ">

@ar2rsawseen Thanks

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