From: Christoph <chr_mail@...>
Date: 2004-12-04T22:51:36+09:00
Subject: Re: Hash#eql? and Hash key testing

Joel VanderWerf schrieb:

>
> The ri docs for Object#eql? say:
>
>      The +eql?+ method returns +true+ if _obj_ and _anObject_ have the
>      same value. Used by +Hash+ to test members for equality.
>
> However, the second sentence doesn't seem to be consistent with the 
> behavior of Hash (and Set):
>
>   h1 = {1=>2, 3=>4}
>   h2 = {1=>2, 3=>4}
>
>   p h1.eql?(h2) # ==> true
>
>   h={h1=>true}
>
>   p h[h1] # ==> true
>   p h[h2] # ==> nil
>
> Based on the docs, I would have expected
>
>   p h[h2] # ==> true
>
> Have I misunderstood?
>
No you have not, however hashes have different
Hash values (their ids - the same is true for Sets)
so all bets are off

----
class A
  def ==(rhs)
    true
  end
 
  alias :eql? :==
end

def test
  a,b = A.new,A.new
  ah = {a  => true }
  bh = {b => true }
  p ah[b]
end

 test # nil
class A
   def hash
    1
   end
end

 test # true

class A
  remove_method :eql?
end


test  # nil
---

/Christoph