Type aliasing to avoid name clash in type refinement

问题

Can I use aliasing so I don't need to change either of the type parameter/member in the following name clash situation:

trait Bar {
  type A
}

trait Foo {
  def get[A]: Option[Bar { type A = A }]  // "illegal cyclic reference"
}

I know I can write

trait Foo {
  def get[A1]: Option[Bar { type A = A1 }]
}

But I would really prefer not to change the type name.

回答1:

You could e.g. do something like this:

trait Bar {
  type A
}

trait Foo {
  type M[X] = Bar { type A = X }
  def get[A]: Option[M[A]]
}

Or inline:

def get[A]: Option[({ type X[Y] = Bar { type A = Y }})#X[A]] = ???

Or, if you prefer:

def get[A]: Option[({ type A1 = A; type X = Bar { type A = A1 }})#X] = ???

来源：https://stackoverflow.com/questions/16375857/type-aliasing-to-avoid-name-clash-in-type-refinement