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digitalmars.D.learn - enum to flags

reply Nicholas Wilson <iamthewilsonator hotmail.com> writes:
so I have a bunch of enums (0 .. n) that i also want to represent 
as flags ( 1 << n foreach n ). Is there anyway to do this other 
than a string mixin?

use like:

enum blah
{
     foo,
     bar,
     baz,
}

alias blahFlags = EnumToFlags!blah;

static assert(blahFlags.baz == 1 << blah.baz)
Sep 28 2015
next sibling parent reply Cauterite <cauterite gmail.com> writes:
On Tuesday, 29 September 2015 at 03:31:44 UTC, Nicholas Wilson 
wrote:

 so I have a bunch of enums (0 .. n) that i also want to 
 represent as flags ( 1 << n foreach n ). Is there anyway to do 
 this other than a string mixin?


You could cheat with operator overloading:

	enum blah {
		foo,
		bar,
		baz,
	};
	
	struct EnumToFlags(alias E) {
		template opDispatch(string Name) {
			enum opDispatch = 1 << __traits(getMember, E, Name);
		};
	};
	
	alias blahFlags = EnumToFlags!blah;
	
	static assert(blahFlags.foo == (1 << blah.foo));
	static assert(blahFlags.bar == (1 << blah.bar));
	static assert(blahFlags.baz == (1 << blah.baz));
Sep 28 2015
parent Nicholas Wilson <iamthewilsonator hotmail.com> writes:
On Tuesday, 29 September 2015 at 06:08:03 UTC, Cauterite wrote:

 On Tuesday, 29 September 2015 at 03:31:44 UTC, Nicholas Wilson 
 wrote:

 so I have a bunch of enums (0 .. n) that i also want to 
 represent as flags ( 1 << n foreach n ). Is there anyway to do 
 this other than a string mixin?


 You could cheat with operator overloading:

 	enum blah {
 		foo,
 		bar,
 		baz,
 	};
 	
 	struct EnumToFlags(alias E) {
 		template opDispatch(string Name) {
 			enum opDispatch = 1 << __traits(getMember, E, Name);
 		};
 	};
 	
 	alias blahFlags = EnumToFlags!blah;
 	
 	static assert(blahFlags.foo == (1 << blah.foo));
 	static assert(blahFlags.bar == (1 << blah.bar));
 	static assert(blahFlags.baz == (1 << blah.baz));


Cheating is always good. I'l probably add some template 
constraints.

Thanks
Nic
Sep 29 2015
prev sibling next sibling parent reply John Colvin <john.loughran.colvin gmail.com> writes:
On Tuesday, 29 September 2015 at 03:31:44 UTC, Nicholas Wilson 
wrote:

 so I have a bunch of enums (0 .. n) that i also want to 
 represent as flags ( 1 << n foreach n ). Is there anyway to do 
 this other than a string mixin?

 use like:

 enum blah
 {
     foo,
     bar,
     baz,
 }

 alias blahFlags = EnumToFlags!blah;

 static assert(blahFlags.baz == 1 << blah.baz)


Answering a slightly different question, I just wanted to be sure 
you're aware of this old idiom:

enum blah
{
     foo = 0b1;
     bar = 0b10;
     baz = 0b100;
     //and so on...
}

auto fdsa = blah.foo | blah.baz;
assert(fdsa & blah.foo);
assert(fdsa & blah.baz);
assert(!(fdsa & blah.bar));
Sep 29 2015
parent Nicholas Wilson <iamthewilsonator hotmail.com> writes:
On Tuesday, 29 September 2015 at 09:18:52 UTC, John Colvin wrote:

 On Tuesday, 29 September 2015 at 03:31:44 UTC, Nicholas Wilson 
 wrote:

 so I have a bunch of enums (0 .. n) that i also want to 
 represent as flags ( 1 << n foreach n ). Is there anyway to do 
 this other than a string mixin?

 use like:

 enum blah
 {
     foo,
     bar,
     baz,
 }

 alias blahFlags = EnumToFlags!blah;

 static assert(blahFlags.baz == 1 << blah.baz)


 Answering a slightly different question, I just wanted to be 
 sure you're aware of this old idiom:

 enum blah
 {
     foo = 0b1;
     bar = 0b10;
     baz = 0b100;
     //and so on...
 }

 auto fdsa = blah.foo | blah.baz;
 assert(fdsa & blah.foo);
 assert(fdsa & blah.baz);
 assert(!(fdsa & blah.bar));


I am. The reason I wanted was so i could easily reorder them 
(logical groupings etc. ) .

Nic
Sep 29 2015
prev sibling parent Meta <jared771 gmail.com> writes:
On Tuesday, 29 September 2015 at 03:31:44 UTC, Nicholas Wilson 
wrote:

 so I have a bunch of enums (0 .. n) that i also want to 
 represent as flags ( 1 << n foreach n ). Is there anyway to do 
 this other than a string mixin?

 use like:

 enum blah
 {
     foo,
     bar,
     baz,
 }

 alias blahFlags = EnumToFlags!blah;

 static assert(blahFlags.baz == 1 << blah.baz)


Take a look at the BitFlags template as well. It won't create 
such an enum for you, but will provide a convenient wrapper for 
using it afterword:
Sep 29 2015