From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-08-03T01:50:26+09:00
Subject: Re: enum collection of constant values

On Wed, 3 Aug 2005, Garance A Drosehn wrote:

> I'd like to have a set of constants for a class, where their values
> need to be unique, and preferably compact.  For instance:
>   SB_NONE = 0; SB_GOOD = 1; SB_BAD = 2; SB_LOGIC_ERR = 3;
>   SB_MAX = SB_LOGIC_ERR
>
> but if I want to modify this list by adding something in the middle,
> then I have to remember to increment (by hand) all the values
> which come after that new value.
>
> In C, I would do something like:
>    typedef enum { SB_NONE, SB_GOOD, SB_BAD,
>        SB_LOGICERR } sb_set;
>
> Looking through the pickaxe book, it looks like the closest thing
> I can do is to create an array of words, and then use the indexes
> of where those words are in the array.  But that isn't really the
> same thing.   I'd like the efficiency of having constant values,
> which would be referred to by name.
>
> (And after I have that for a compact set of values, I'd want a
> similar feature which would give me a bit-wise unique set of
> values.  Eg:  SB_MODA = 1; SB_MODB = 2; SB_MODC = 4;
> SB_MODD = 8; -- such that I could combine the values together
> using '|', and tell which values were 'or'-ed together to get that
> combined value...)
>
> -- 
> Garance Alistair Drosehn     =             drosihn@gmail.com
> Senior Systems Programmer               or   gad@FreeBSD.org
> Rensselaer Polytechnic Institute;             Troy, NY;  USA

class methods are your friend

     harp:~ > cat a.rb
     module Enum
       def self::included other
         other.module_eval do
           def self::enum(*list)
             list.flatten.each_with_index{|e, i| const_set e.to_s.intern, i}
           end
           def self::bit_enum(*list)
             list.flatten.each_with_index{|e, i| const_set e.to_s.intern,  2 ** i}
           end
         end
       end
     end

     class C
       include Enum

       enum %w(
         FOO
         BAR
         FOOBAR
         BARFOO
       )
     end

     class B
       include Enum

       bit_enum %w(
         FOO
         BAR
         FOOBAR
         BARFOO
       )
     end

     p C::FOO
     p C::BARFOO

     printf "0b%8.8b\n", B::FOO
     printf "0b%8.8b\n", B::BARFOO


     harp:~ > ruby a.rb
     0
     3
     0b00000001
     0b00001000


cheers.

-a
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