C like macro is useful

[Jarrett Billingsley]

"downs" <default_357-line at yahoo.de> wrote in message 
news:g67bqp$20ma$2 at digitalmars.com...

> version(v1) auto cond = a == b;
> else auto cond = a != b;
>
> What's the problem again?

That's one solution for one case.  It does not hold up in the general case. 
How about the enum example?  How about differing declarations in general? 
How about trying to make class invariants work in both D1 and D2?