But for the promotion possibility, one can only choose either a Queen, a Rook, a Knight or a BIshop.

I see

you should add a marker interface

interface Promotable

to those classes and use

fun <T> foo(factory: () -> T) where T: ChessPiece, T: Promotable

Oh, why I did not thought about that ? Thank you very much 😄

you're welcome

How could I turn T to a reference parameter instead of instance one ?

what do you mean by reference parameter?

In fact I would like to pass Queen::class for example

(Reference in not the good word)

ok, then you write

fun <T> foo(klass: KClass<T>) where T: ChessPiece, T: Promotable

Thank you very much 😄

Sorry again, as a last issue

Oh wait, I think I know why (out keyword, maybe)

Finally still got blocked

@User uploaded a file: Untitled and commented: IDE complains about the fact he got KClass<Queen>.

instead of KClass<T>

why do you need the default parameter?

this works:

fun foo() {
    doMove(1 to 1, 2 to 2, Queen::class)
}
fun <T> doMove(startSquare: Pair<Int, Int>, endSquare: Pair<Int, Int>,
               promotionPiece: KClass<out T>): ChessGame where T: ChessPiece, T: Promotable {
    TODO()
}

Because I wanted to make a general purpose move validator : one for regular moves so that promotion parameter is not needed and one for promotion moves where the promotion piece is needed. Unfortunately, the nature of the move can only be determinated by the two cells.

Thank you. I replace my code with your snippet. 😄

you can overload your function if you want a default value

Oh thank you. I will do this way 😄

Yes : no compilation error. Thank you very much 😄

How about null for no promotion?

I don't like very much to use null for this case.

what's the point of generics then

The @kirillrakhman solution is very good

@kirillrakhman Good question

Maybe null could be a good alternative finally

Null value are simple to deal with