Restriction on interface function types

[monarch_dodra]

On Wednesday, 12 March 2014 at 10:57:10 UTC, Steve Teale wrote:
> interface I
> {
>    auto myType();
> }
>
> class A: I
> {
>    auto myType() { return cast(A) null; }
> }
>
> void main()
> {
>    I x = getSomeI();
>    typeof(x.myType()) y;
> }

Seems like you want covariance? I don't see how else having an 
interface that returns "auto" could work.

That said, I'd expect this to work:

//----
interface I
{
    I myType();
}

class A: I
{
    //auto myType() { return cast(A) null; } //Nope
    A myType() { return cast(A) null; } //OK
}
//----

But app