From: "Florian Groß" <florgro@...>
Date: 2006-04-13T23:38:03+09:00
Subject: Re: Array#-

jogloran wrote:

> I need items to be compared based on their values, and not by object
> equality, so I provide #== for the array elements. The problem is that I've
> been trying to use Array#- as a set difference-like operation, and it
> doesn't seem to respect any kind of user-provided means of defining
> equality. A look into the Ruby source seems to indicate that it works by
> populating a hash with the elements of the second array, then appending to
> the result array if an element of the first array is in the hash. Does this
> mean that it is impossible to get the behaviour I want from Array#- as it is
> implemented?

Nope, you just need to redefine hash and alias == as eql?.

This will work:

def hash()
   # But it's a good idea to actually define this in a meaningful way so
   # that putting the object into hashes is efficient.
   0
end

alias :eql? :==

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