Given
trait Foo[T <: Bar] {
def foo: T
}
why does the compiler NOT interpret signature like
def foo(f: Foo[_])
to mean that the unknown _ must be a type of Bar. Instead, it forces me to do this
def foo(f: Foo[_ <: Bar])
which complicates signatures. I'm sure the compiler must be right and I'm missing some subtlety but clearly a Foo[X] where X is NOT some kind of Bar so not possible by construction, so why?
Thank you.
In short - seems to be a deficiency of the compiler and an open question whether to address it. Fixing it may have unintended consequences but it's been raised often enough to still be considered seriously as a possible fix. Here are some of the most relevant and still open Bugs tickets.
P.S. It seems that Dotty does honor such bounds so they may well fix it!