Why is Phobos' isIntegral different from the built-in trait of the very same name?

[Walter Bright]

On 10/17/2021 12:19 PM, Andrei Alexandrescu wrote:
> As a pattern, I note just how complex the type system is and how many special 
> cases there are:

and:

 > Do conversions on the call side.

More generally, "is a" and "is implicitly convertible to a" must be treated 
distinctly as separate operations.