Re: Re: Scala - a Roadmap

On Mon, Jun 15, 2015 at 5:08 AM, Shelby <[email protected]> wrote:
> How would the unification of higher-kinded and abstract types express the
> following semantics?
>
> trait Functor[T, Subtype[T] <: Functor[T, Subtype[T]] {
>   def map : (T => R) => Subtype[R]
> }
>
> Am I correct to assume the following?
>
> trait Functor {
>   type T
>   type Subtype <: Functor
>   def map : (T => R) => Subtype
> }
>
That would lose information. I believe you have to write it like this:

trait Functor { functor =>
  type T
  type Subtype <: Functor { type T = functor.T }
  def map[R] : (T => R) => Subtype { type T = R }
}

To avoid misunderstanding (because I found many people do
misunderstand this point): That would be a compiler expansion; you
will usually still write the original parameterized version:

> trait Functor[T, Subtype[T] <: Functor[T, Subtype[T]] {
>   def map : (T => R) => Subtype[R]
> }
>

Cheers

 - Martin

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-- 
Martin Odersky
EPFL

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