Getting the template name of a template instantiation

[Nordlöw via Digitalmars-d-learn]

If I have a template parameter

    E = S!int

where

    struct S(T) { S x; }

how can I extract the template name part `S` from E`?

Something like:

    static assert(is(templateName!(S!int) == S));

Is this already in Phobos somewhere?