Declaration site variance problem


Hi friends

In funKTionale I use declaration-site variance for Option and Either types

In M10 the compiler is marking this as an error

public fun getOrElse(default: () -> T): T {
    return if (isEmpty()) {
    } else {

The error is "Error:(41, 41) Kotlin: Type parameter T is declared as 'out' but occurs in 'in' position in type () -> T"

Technically that “T” is an “out” 'cause is the return of “default” function… an out.

Am I right or I missing somethig?


The compiler is right: taking a function that returns T is equivalent to taking a T. Allowing such methods would have made it possible to get an exception at runtime.

I’d suggest using extension functions in this case


If that was the case, it would be possible to workaround these compiler errors by changing parameter of type T to the parameter of a functional type returning T, wouldn't it? :)

In fact ‘default’ is in a contravariant (in) position, and covariant (out) of contravariant is still contravariant


Thanks for the idea