And a `MutableList<Object>` is a `MutableLis...

# announcements

[diesieben07]

And a MutableList<Object> is a MutableList<in CharSequence> because you can put any CharSequence into a list of objects.

[paulex]

Please i'm very Sorry to bother you:
MutableList<in Charsequence>...
var x:MutableList<Charsequence>
var y:MutableList<String>
why is this not correct;

x = y

but

y = x

is correct

[diesieben07]

Apart from the fact that val cannot be reassigned: Both are not correct.

[paulex]

open class Animal{
    private var id:Int = 0
}

data class Cat(
    private var name:String = ""
):Animal()

interface ViewInterface<in T:Animal> {
    fun setAnimal(animal:T)
}

fun main(args:Array<String>){
    
    var x:ViewInterface<Cat> = object:ViewInterface<Cat>{
        override fun setAnimal(s:Cat){
			println("Cat was set")
        } 
    }

    var y:ViewInterface<Animal> = object:ViewInterface<Animal>{
        override fun setAnimal(s:Animal){
			println("Animal was set")
        } 
    }
        
//     x.setAnimal(Animal())
    
    x = y //*This works*
//     y = x //This doesnt
    
//     x.setAnimal(Animal())
    
}

[diesieben07]

x is of type ViewInterface<Cat>. Since ViewInterface uses declaration-site variance, this is really ViewInterface<in Cat> and ViewInterface<Animal> is assignable to that.

[diesieben07]

Because if something can take in a Animal (your y) it can also take in a Cat.

[diesieben07]

ViewInterface<in Cat> means "anything that can take a Cat". And your y fits that, it can even take any animal, which includes cats.

[paulex]

but why would
y = x // fail
y is animal
and i would expect that it to take take a cat x

however if it was covariant
y = x is acceptable
i know im missing a point buh i'm hoping to get it

[diesieben07]

y is ViewInterface<in Animal>, i.e. "i can take animals". But x can only take cats, not any animal.

[paulex]

I want to say i big thank you for thanking out time to explain this..