Hi there, i'm trying to understand generics inside...

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[felislynx]

Hi there, i'm trying to understand generics inside kotlin and i'm blocked. Given sample below i wanted to use in base class my FooList as param and extend this class where i'm using BarList. But i'm unable to

open class Foo {

}
class Bar:Foo(){

}
open class FooList {
	open var list:List<Foo>?=null
}
class BarList:FooList(){
	override var list:List<Bar>?=null
}
open class BaseTest {
 open var llist:List<FooList>?=null
}
class BaseTestTwo : BaseTest {
	override var llist:List<BarList>?=null
}

[Andreas Sinz]

is BaseTestTwo failing?

[felislynx]

Yes

[felislynx]

normally in Java i would use <? extends FooList>

[felislynx]

sorry, i've made one mistake rewriting this sample

[felislynx]

open class FooList<T:Foo> {
    open var list: List<T>? = null
}
class BarList : FooList<Bar>() {
    override var list: List<Bar>? = null
}

[Andreas Sinz]

the problem is that list: List<T>? is a var and thus is reassignable

[felislynx]

ide error: var property type List<BarList> which is not a type of overriden public var list List<FooList<Foo>>

[felislynx]

i've many times overrided default value of var or val in subclass but i didn't changed type of it during process

[Andreas Sinz]

FooList<T: Foo> is invariant, that means FooList<Bar> is not a subtype of FooList<Foo>

[felislynx]

is this achiveable ?

[felislynx]

i mean what i meant, not how i did 🙂

[Andreas Sinz]

if you change it to val and use FooList<out T: Foo>

[felislynx]

but in doing it as val, i cannot reasign it

[felislynx]

there is no other way?

[Andreas Sinz]

nope, not without losing type-safety

[Andreas Sinz]

if you can show me more code around it, maybe we can work out a better approach

[felislynx]

Foo,Bar,FooList,BarList are classes used in retrofit

[felislynx]

BaseTest and BaseTestTwo are classes representing ViewModel

[felislynx]

where Base is in main module, and Two i is in other flavors

[Andreas Sinz]

and why do you need to reassign the list?

[felislynx]

open val lists: MutableLiveData<Pair<String, ArrayList<Foo>>> = MutableLiveData()

[felislynx]

after new network call

[felislynx]

i have to use lists.value = Pair("Some String",response.body())