[phobos] sizediff_t

[Walter Bright]

Yes we do, ptrdiff_t, defined in object.

Andrei Alexandrescu wrote:
> One question - we don't have a type for the difference of two size_t 
> objects. That would be int on m32 and long on m64. C has historically 
> used ptrdiff_t for that, but not all size differences are pointer 
> differences, so gnu has acknowledged that by defining ssize_t ("signed 
> size_t" I suppose).
>
> While being in a crunch making some 64-bit changes I defined the type 
> sizediff_t. I wonder if that's okay as a permanent solution.
>