From: ara.t.howard@...
Date: 2006-10-11T00:44:36+09:00
Subject: Re: Removing Duplicate Objects from Object List

On Wed, 11 Oct 2006, Mike wrote:

> uniq is failing because, even though the attributes of each instance of
> the rule is 'eq' to the other, the compared instances are different.
>
> class Foo
> def initialize(a,b)
>  @a = a
>  @b = b
> end
> end
>
> x = [Foo.new(:a, :b), Foo.new(:c, :d), Foo.new(:a, :b)]
> p x
> p x.uniq
>
> ruby tst.rb
> [#<Foo:0x3b6128 @a=:a, @b=:b>, #<Foo:0x3b6114 @a=:c, @b=:d>,
> #<Foo:0x3b6100 @a=:a, @b=:b>]
> [#<Foo:0x3b6128 @a=:a, @b=:b>, #<Foo:0x3b6114 @a=:c, @b=:d>,
> #<Foo:0x3b6100 @a=:a, @b=:b>]
>
> I tried defining eq? and hash and uniq still fails.  hash returns
> identical values for objects with identical content and eq? returns
> true in this case, but uniq does not remove them.


harp:~ > cat a.rb
class Foo
   ATTRIBUTES = %w( a b )
   ATTRIBUTES.each{|at| attr at}

   def initialize(a,b) @a, @b = a, b end
   def parts() ATTRIBUTES.map{|at| send at} end
   def eql?(other) parts == other.parts end
   def hash() parts.hash end
end

p [ Foo.new(:a, :b), Foo.new(:c, :d), Foo.new(:a, :b) ]
p [ Foo.new(:a, :b), Foo.new(:c, :d), Foo.new(:a, :b) ].uniq


harp:~ > ruby a.rb
[#<Foo:0xb75d137c @a=:a, @b=:b>, #<Foo:0xb75d1368 @a=:c, @b=:d>, #<Foo:0xb75d1340 @a=:a, @b=:b>]
[#<Foo:0xb75d1214 @a=:a, @b=:b>, #<Foo:0xb75d1200 @a=:c, @b=:d>]



-a
-- 
my religion is very simple.  my religion is kindness. -- the dalai lama