check instance of nested variadic template

[Basile B. via Digitalmars-d-learn]

On Saturday, 5 November 2016 at 14:37:53 UTC, Basile B. wrote:
> On Saturday, 5 November 2016 at 13:34:51 UTC, Gianni Pisetta 
> wrote:
>> [...]
>
> Indeed, I've been fighting against that since a few minutes. We 
> cant select the Base of an eponymous template.
>
>
> template isEponymousTemplate(T)
> {
>     static if (is(T == class) || is(T == interface) || is(T == 
> struct) || is(T == union))
>     {
>         enum p = __traits(parent, T).stringof == T.stringof;
>         enum isEponymousTemplate = p && isTemplateInstance!T;
>     }
>     else
>         enum isEponymousTemplate = false;
> }
>
> template TemplateBase(T : Base!Args, alias Base, Args...)
> if (is(T == class) || is(T == interface) || is(T == struct) || 
> is(T == union))
> {
>     alias TemplateBase = Base;
> }

To be more accurate the template base can be selected for

     template A(T) {class A{}}

but not for

     class A(T){}