...it seems fine at least with a template specialization:

//struct S(T)
    //if (is(T...

This is in bugzilla:
https://issues.dlang.org/show_bug.cgi?id=6269

...dmd pull request #14465 "fix 23355: invalid template parameter loses error location in some cases...

...dmd pull request #14465 "fix 23355: invalid template parameter loses error location in some cases...

https://issues.dlang.org/show_bug.cgi?id=23355

mhh <maxhaton@gmail.com> changed:

           What...

...id=23355

          Issue ID: 23355
           Summary: invalid template parameter loses error location in
                    some cases...

Apologies, I only read your comment now.

Thank you, this is indeed what I was...

I am aware of the differences when the if statement fails, though the intent remains...

...the desired constraint cannot be expressed using template specializations. For example:

```d
auto fun(R...

...by Introspection (DbI), the second is a template with requirements.

There are better ways than...