From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-09-15T00:20:04+09:00
Subject: Re: Sets, uniqueness not unique.


> OK, it seems I'm thinking along the right lines now.  Here is what I did in
> the end:

< snip code >

> I was particularly pleased to be able not to repeat the FIELDS, by means of
> attr_accessor, and that the idea of doing (self.class)::FIELDS actually
> worked.

i do alot of that type of thing and use my traits lib a lot for it - it can
make it pretty compact.  for instance:

   harp:~ > cat a.rb
   require 'md5'
   require 'traits'

   module TraitCollection
     def initialize(*list)
       list = [ list ].flatten
       wt.each_with_index do |t,i|
         v = list[i] or
           raise ArgumentError, "no <#{ t }> given in <#{ list.inspect }>!"
         send t, v
       end
     end
     def to_s
       (rt.map{|t| [t, send(t)].join '='}. << "hash=#{ hash }").inspect
     end
     alias inspect to_s
     def hash
       rt.inject(::MD5::new()){|d,m| d << send(m)}.hexdigest.hex
     end
     def eql?(other)
       rt.inject(true){|b,v| b && (send(v) == other.send(v)) rescue false}
     end
     def wt; self::class::writer_traits; end
     def rt; self::class::reader_traits; end
     def self::included other
       super; class << other; class << self; alias [] new; end; end
     end
   end

   class Student
     include TraitCollection
     traits *%w( forename surname birth_dt picture coll_status )
   end
   class Course
     include TraitCollection
     traits *%w( aos_code dept_code aos_type full_desc )
   end

   require 'set'

   sset = Set::new
   s0, s1 = Student[%w( a b c d e )], Student[%w( f g h i j )]
   sset.add s0
   42.times{ sset.add s1 }
   p sset

   cset = Set::new
   c0, c1 = Course[%w( a b c d )], Course[%w( e f g h )]
   cset.add c0
   42.times{ cset.add c1 }
   p cset

   harp:~ > ruby a.rb
   #<Set: {["forename=a", "coll_status=b", "birth_dt=c", "picture=d", "surname=e", "hash=227748192848680293725464448333830731654"], ["forename=f", "coll_status=g", "birth_dt=h", "picture=i", "surname=j", "hash=116663401890982171087417074910604104991"]}>

   #<Set: {["dept_code=a", "full_desc=b", "aos_code=c", "aos_type=d", "hash=301716283811389038011477436469853762335"], ["dept_code=e", "full_desc=f", "aos_code=g", "aos_type=h", "hash=41821698252824551223787888325781077799"]}>


cheers.

-a
-- 
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