an enum inside another enum

[Simen Kjaeraas]

On Thu, 26 Jul 2012 18:08:24 +0200, maarten van damme  
<maartenvd1994 at gmail.com> wrote:

> The newly generated ExtendEnum will try to convert my old enum with
> string fields to integer fields. the mixin should generated
> "ExtendEnum : string" when passing in an enum with type string. Same
> problem apply's to the second line of this sniped. enum a doesn't have
> a type yet so it will try to convert everything to ints.
>
>
> As I seem to run into problems few others have, is my usage of enum's  
> incorrect?

I had not considered non-int enums in the first version. There is nothing
wrong with the way you use enums, though I haven't yet found a good reason
to extend them (I just like to :p).

Fixed version below:


import std.traits : OriginalType;

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: OriginalType!T {"~s~"}");})))
{
     mixin(
     "enum ExtendEnum : OriginalType!T {"
     ~ EnumDefAsString!T() ~ s
     ~ "}");
}

enum bar : string {
	a = "a",
	b = "r",
	c = "t",
}

enum baz {
     a = 1,
     b = 2,
     c = 3,
}

unittest {
     alias ExtendEnum!(bar, q{ // Usage example here.
         d = "Text"
     }) bar2;

     foreach (i, e; __traits(allMembers, bar2)) {
         static assert( e == ["a", "b", "c", "d"][i] );
     }
     assert( bar2.a == bar.a );
     assert( bar2.b == bar.b );
     assert( bar2.c == bar.c );
     assert( bar2.d == "Text" );
     static assert(!is(typeof( ExtendEnum!(int, "a"))));
     static assert(!is(typeof( ExtendEnum!(bar, "25"))));
}

unittest {
     alias ExtendEnum!(baz, q{ // Usage example here.
         d = 25
     }) baz2;

     foreach (i, e; __traits(allMembers, baz2)) {
         static assert( e == ["a", "b", "c", "d"][i] );
     }
     assert( baz2.a == baz.a );
     assert( baz2.b == baz.b );
     assert( baz2.c == baz.c );
     assert( baz2.d == 25 );
     static assert(!is(typeof( ExtendEnum!(baz, "25"))));
}

void main() {
}
-- 
Simen