A possible enhancement related to is()

[Jakob Ovrum]

On Wednesday, 29 January 2014 at 02:30:00 UTC, bearophile wrote:
> In std.typecons there is this template, that tells if a given 
> type is any tuple, this means if it's the instantiation of a 
> Tuple with any argument type:
>
>
> template isTuple(T)
> {
>     static if (is(Unqual!T Unused : Tuple!Specs, Specs...))
>     {
>         enum isTuple = true;
>     }
>     else
>     {
>         enum isTuple = false;
>     }
> }
>
>
> Do you think it's worth a D enhancement request to be able to 
> write that code like this?
>
> enum isTuple(T) = is(Unqual!T Unused : Tuple!Specs, Specs...);
>
> Bye,
> bearophile

We can already do this, but you have to omit the `Unused` alias 
(a semi-recent enhancement allows for that):

---
import std.traits : Unqual;

struct Tuple(Args...) {}

enum isTuple(T) = is(Unqual!T : Tuple!Types, Types...);

void main()
{
	Tuple!(int, string) t;
	static assert(isTuple!(typeof(t)));
}
---

On a related note, I would like the body of a template to be able 
to access aliases introduced in IsExpression's in the template's 
constraints.