From: Caleb Clausen <vikkous@...>
Date: 2010-06-12T04:11:00+09:00
Subject: Re: comparing objects

On 6/11/10, Robert Dober <robert.dober@gmail.com> wrote:
> OP wanted to use Array#&, and Array#&, for a reason not too clear to
> me, uses Object#eql? instead of Object#== I did discourage the
> overloading of Object#eql? and Object#hash for *that purpose*.

Array#& uses eql? instead of == because internally, it works something
like this:

class Array
  def &(other)
    h1={}
    other.each{|x| h1[x]=true}
    select{|x| h1[x] }
  end
end

In other words, it creates a (hash) index to get a speedup. (From
O(M*N) to O(M+N).)