enums extension

[Simen Kjaeraas]

On Wed, 16 May 2012 06:22:15 +0200, Comrad  
<comrad.karlovich at googlemail.com> wrote:

> Dear developers and community,
> I want to draw you attention to the topic which was already discussed  
> here:
> http://forum.dlang.org/thread/9to6n8$12d6$1@digitaldaemon.com
> and here:
> http://forum.dlang.org/thread/bl1n0e$1km5$1@digitaldaemon.com
>
> My question is: was something similar already done? are there some plans  
> to do that?

I have implemented this functionality in user code, with some caveats:

module enumMagic;

string EnumDefAsString(T)()
	if (is(T == enum))
{
	string result = "";
	foreach (e; __traits(allMembers, T)) {
		result ~= e ~ " = T." ~ e ~ ",";
	}
	return result;
}

template ExtendEnum(T, string s)
	if (is(T == enum) &&
		is(typeof({mixin("enum a{"~s~"}");})))
{
	mixin(
		"enum ExtendEnum {"
		~ EnumDefAsString!T()
		~ s
		~ "}");
}

unittest {
     enum Foo {
         a,
         b,
         c
     }
     alias ExtendEnum!( Foo, q{
         d,
         e
     }) Bar;

     Bar b;
     b = Bar.a; // Look ma, I stole this from Foo!
     b = Bar.d;
     assert( Bar.a == Foo.a ); // Can compare the two.
     //b = Foo.a; // But cannot assign from one to the other.
}

void main( ) {
}

A library implementation with the missing features is possible, but would  
use a
struct instead of an enum, an be a rather larger piece of code than this.