Pattern matching is-expressions

[Stefan Koch]

On Wednesday, 19 August 2020 at 13:07:40 UTC, Stefan Koch wrote:
>
> And I think I have found a way to support them within the 
> typefunctions.
> is(T S == super) would become
> auto f(alias T)
> {
>    static literal bool r = is(T S == super);
>    // here alias S = (r ? SuperTupleOf(T) : ErrorType) is 
> automatically declared.
>    // where ErrorType is the value for which `!is(ErrorType)` 
> is true
> }
>

Back to the drawing board, it turns out my initial fears were 
appropriate.
Making an identifier into a variable declaration depending on 
whether you are in a type function or not; Is a funky thing to do.

I'll to go with additional __traits.

Besides I do think that __traits(getSuperType, T)
does look more readable than is(T S == super)

even though it does not give you the "symbolic equation" feeling 
:)