Restriction on interface function types

[Steven Schveighoffer]

On Wed, 12 Mar 2014 09:13:08 -0400, Steve Teale  
<steve.teale at britseyeview.com> wrote:

> On Wednesday, 12 March 2014 at 11:56:43 UTC, Steven Schveighoffer wrote:
>> On Wed, 12 Mar 2014 06:57:08 -0400, Steve Teale  
>> <steve.teale at britseyeview.com> wrote:
>>
>>
>> What you want simply isn't possible. An interface binds at runtime, and  
>> you need to declare types at compile-time. You can't use an interface  
>> method to define the type of y.
>>
>> -Steve
>
> Steve
>
> OK, it was a bad illustrative example, but
>
> (cast(typeof(a.myType()) whatever).foo();
>
> could be useful, when foo() is not in the interface.
>
> It was the failure of auto in an interface that I was remarking on -  
> should at least be documented. Also the covariant return values as  
> suggested by md don't work either.

Auto doesn't work if you don't define what it returns. Auto is not a type  
in itself, it means "infer the type". If there's nothing to infer with,  
it's an error.

-Steve