How can I distinguish an enum constant from an actual enum at compile time?

[Gary Willoughby via Digitalmars-d-learn]

On Friday, 30 October 2015 at 12:03:50 UTC, TheFlyingFiddle wrote:
> pragma(msg, is(b == enum)); //True
> pragma(msg, is(a == enum)); //False.

enum isEnum(alias e) = is(e == enum);

isEnum!(a)
isEnum!(b)

;)