From: Robert Klemme <bob.news@...>
Date: 2004-06-18T16:33:22+09:00
Subject: Re: How to make generic #== method?


"Zakaria" <zakaria@suarametro.com> schrieb im Newsbeitrag
news:20040617211611.GA4734@zakbox.local...
> Hi,
>
> Currently I got many simple class which is just a simple record-like.
> An example
> -----------------------------------
> class LoopTag # :nodoc:
>   attr_reader :param
>   attr_reader :contents
>
>   def initialize(param)
>     @param, @contents = param, []
>   end
>
>   def ==(other)
>     return false unless other.class == self.class
>     return other.param == @param && other.contents == @contents
>   end
> end
> ------------------------------------
> and I got a couple more class like this.
>
> Is there a way to make a generic #== or some Module that I can include ?
>
> I surely need it to do assert_equal on unit test.
> You know, I just waste a couple hour tracking bug that doesn't exists
> because I forgot to implement #== :)

module MemberEquivalence
  def ==(o)
    instance_variables.each do |var|
      return false unless instance_variable_get(var) ==
o.instance_variable_get(var)
    end

    true
  end

  def hash
    h = 0

    instance_variables.each do |var|
      val = instance_variable_get(var)
      h ^= val.hash unless val.nil?
    end

    h
  end

  alias :eql? :==
end

class Foo
  include MemberEquivalence

  attr_accessor :foo, :bar
end


>> f=Foo.new
=> #<Foo:0x10194988>
>> g=Foo.new
=> #<Foo:0x1018f918>
>> f == g
=> true
>> f.foo = "x"
=> "x"
>> f == g
=> false
>> f.foo = nil
=> nil
>> f == g
=> true
>> f.hash
=> 0
>> g.hash
=> 0
>> f.eql? g
=> true
>> h={ f => 1 }
=> {#<Foo:0x10194988 @foo=nil>=>1}
>> h[g]
=> 1

Regards

    robert