From: Garance A Drosehn <drosihn@...>
Date: 2007-02-06T08:33:58+09:00
Subject: Re: Enumerated Types

On 2/3/07, Dan Stevens (IAmAI) <dan.stevens.iamai@gmail.com> wrote:
> As part of a solution, I wish the value of an attribute to be one of a
> finite set of values, in other words I believe I want an 'enumerated
> type'. I've look at the 'Enumerable' and 'Enumerator' class and they
> appear to me to be unrelated to what I wish to achieve (correct me if
> I'm wrong).
>
> I could do the traditional method of named constants with integer
> values but I can't help feeling that there must be a class or some
> nice method of doing this. Any advice would be appreciated.

I picked up this snippet of code:

# -------+---------+---------+-------- + --------+---------+---------+---------+
#   Add methods enum and bit_enum to the Object class, thus making it much
#   easier and less error-prone to define a long list of constants in a
#   class.  This idea comes from Ara.T.Howard@noaa, in a posting to ruby-talk
#   on August 2, 2005 (in reply to a question).  These work very nicely with
#   a word-list array as generated via %w().  Very clever!
#
class Object
    def enum_constants(*list)
	mc = Module === self ? self : self.class
	list.flatten.each_with_index{|e, i| mc.const_set e.to_s.intern, i}
    end
    def enum_bit_constants(*list)
	mc = Module === self ? self : self.class
	list.flatten.each_with_index{|e, i| mc.const_set e.to_s.intern, 2 ** i}
    end
end
# -------+---------+---------+-------- + --------+---------+---------+---------+

An example of using it:

    #   Constants that define all categories of packets which we recognize.
    enum_constants %w(
	  SBC_NONE  SBC_ARRAY  SBC_NONUSER  SBC_NO_IDSTR
	  SBC_IGNFAIL   SBC_ALL
	  SBC_UNMATCHED )

The difference between enum_constants() and enum_bit_constants is
that enum_constants will define the values as 1, 2, 3, 4, 5, etc, while
enum_bit_constants will define them as 1,2,4,8,16,32.  You can 'or'
the enum_bit_constant values together, and each one is a separate
bit so it won't clobber any other bit constant.

If you are not used to the %w() method of quoting, note that you only
put the names you want in there.  You do *not* separate them with
commas!

-- 
Garance Alistair Drosehn     =             drosihn@gmail.com
Senior Systems Programmer
Rensselaer Polytechnic Institute;             Troy, NY;  USA