How to infer the right type parameter from a projection type?

Question

I have some troubles having Scala to infer the right type from a type projection.

Consider the following:

trait Foo {
  type X
}

trait Bar extends Foo {         


        

Answer 1

The program compiles by adding this implicit conversion in the context:

implicit def f(x: Bar#X): Foo#X = x

As this implicit conversion is correct for any F <: Foo, I wonder why the compiler does not do that by itself.