Why it does not allow to assign descendant class ?

interface TopicDelegate<T: ProfileItem> {
    val title: Int
}

class DistrictDelegate(val api: INetworkApi): TopicDelegate<District> {
    override val title: Int = R.string.choose_districts
}

abstract class TopicFragment<T: ProfileItem> : BaseFragment() {
    private var modeDelegate: TopicDelegate<T> = DistrictDelegate(mNetworkApi) //does not work
    //Type mismatch. Required: TopicDelegate<T> Found: DistrictDelegate
}

DistrictDelegate

is a

TopicDelegate<District>

, but a

TopicDelegate<T>

is required.

T

might not be

District

.

District extends ProfileItem

so

TopicDelegate<District>

should fit into

TopicDelegate<T: ProfileItem>

right ?

No.

T

is a parameter, it may stand for anything that extends

ProfileItem

. So if

T

is actually a

SomeOtherProfileItem

, you can't put a

District

in there.