Generating enum members

Mar 15

1 day ago

Hello everyone.
It's my first time starting a thread here please have patience and let me know if there is anything i have done wrong!

I'm currently doing a project where there are two pretty lengthy enums whose members depend on each other.

Declaring one after the other makes it hard to double check that i haven't missed anything, which is why i'm trying to make a template mixin where i can declare the members together and the template does all the appropriate sorting.
I'm not having any luck in generating the enums though.

The simplified version of what i need would be

mixin template create_enum(alias members) {
  enum enumname {
    static foreach(member; members) {
      mixin(member.stringof,",");
    }
  }
}

which obviously doesn't work.

Is it possible at all to do something like this in D?

Thank you for the help!

On Sat, Mar 15, 2025 at 02:47:01PM +0000, Milli via Digitalmars-d wrote: [...] > I'm currently doing a project where there are two pretty lengthy enums whose members depend on each other. > > Declaring one after the other makes it hard to double check that i > haven't missed anything, which is why i'm trying to make a template > mixin where i can declare the members together and the template does > all the appropriate sorting. > I'm not having any luck in generating the enums though. > > The simplified version of what i need would be > ```D > mixin template create_enum(alias members) { > enum enumname { > static foreach(member; members) { > mixin(member.stringof,","); > } > } > } > ``` > which obviously doesn't work. > > Is it possible at all to do something like this in D? [...] Of course it's possible. D is the king of meta-programming, and something like this is right up its alley. What you want is a string mixin + CTFE: string create_enum(string[] members) { string code = "enum MyEnum { "; foreach (memb; members) { code ~= memb ~ ", "; } code ~= "}"; return code; } mixin(create_enum([ "memb1", "memb2", "memb3" ]); T -- Knowledge is that area of ignorance that we arrange and classify. -- Ambrose Bierce

On Saturday, 15 March 2025 at 15:08:06 UTC, H. S. Teoh wrote: oh my i don't know how i missed this feature of D altogether! > What you want is a string mixin + CTFE: CTFE simplifies greatly how i can approach my problem, thank you a lot!

1 day ago

Re: Generating enum members

Posted by cc
in reply to Milli

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Posted in reply to Milli

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On Saturday, 15 March 2025 at 14:47:01 UTC, Milli wrote:

Hello everyone.
It's my first time starting a thread here please have patience and let me know if there is anything i have done wrong!

I'm currently doing a project where there are two pretty lengthy enums whose members depend on each other.

The simplified version of what i need would be

mixin template create_enum(alias members) {
  enum enumname {
    static foreach(member; members) {
      mixin(member.stringof,",");
    }
  }
}

which obviously doesn't work.

Is it possible at all to do something like this in D?

Thank you for the help!

If you have a 1:1 relationship between the enums, you could also declare one first as normal and then use templates/mixins to generate the second based on the first:

enum FooA {
	RED = 1,
	GREEN = 2,
	BLUE = 4,
}
mixin(cloneEnum!(FooA, "FooB"));
string cloneEnum(E, string name)() {
	string s = "enum "~name~" {";
	foreach (member; EnumMembers!E) {
		s ~= format("%s = %s.%s,", member, E.stringof, member);
	}
	s ~= "}";
	return s;
}

void main() {
	assert(cast(int) FooA.BLUE == cast(int) FooB.BLUE);
}

And of course you can modify the function if you need any special logic to exclude or modify some members.

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