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trait A {
type m[+x]
}
trait A2 {
type m[+x <: String]
}
trait A3 {
type m[x]
}
trait FooCov[+x]
trait FooCon[-x]
trait FooBound[+x <: String]
trait BOk1 extends A {
type m[+x] = FooCov[x]
}
trait BOk2 extends A2 {
type m[+x <: String] = FooBound[x]
}
trait BOk3 extends A2 {
type m[+x] = FooCov[x] // weaker bound
}
trait BOk4 extends A3 {
type m[+x] = FooCov[x] // weaker variance
}
// there are two aspects to check:
// does type alias signature (not considering RHS) correspond to abstract type member in super class
// does RHS correspond to the type alias sig
trait BInv extends A{
type m[x] = FooCov[x] // error: invariant x in alias def
}
trait BCon extends A{
type m[-x] = FooCon[x] // error: contravariant x
}
trait BBound extends A{
type m[+x <: String] = FooBound[x] // error: x with stricter bound
}
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