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digitalmars.D - Generating enum members

reply Milli <alezardo02 gmail.com> writes:
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
```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?

Thank you for the help!
Mar 15 2025
next sibling parent reply "H. S. Teoh" <hsteoh qfbox.info> writes:
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
Mar 15 2025
parent Milli <alezardo02 gmail.com> writes:
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!
Mar 15 2025
prev sibling parent cc <us86kj+3rxcwe3ebdv7w grr.la> writes:
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.

 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?

 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:
```d
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.
Mar 27 2025