Add enum E(T) = expression; eponymous template support

Abstract

This pattern has become quite common in D:

   template isIntegral(T) {      enum isIntegral = is(T : long) || is(T : ulong) || ...;    }

Analogously to struct S(T), the enum manifest constant could be written as:

   enum isIntegral(T) = is(T : long) || is(T : ulong) || ...;

This is a natural fit for D. It does not break any existing code, and is simple to implement - it’s just a rewrite in the parser.

Rationale

The pattern is common, and a bit awkward. It’s worth supporting the new syntactic sugar.

Copyright

This document has been placed in the Public Domain.