From: Caleb Clausen <vikkous@...>
Date: 2010-03-03T04:36:44+09:00
Subject: Re: Array#join using to_a if defined

On 3/1/10, Benoit Daloze <eregontp@gmail.com> wrote:
> Also, while playing with Array, using Array#&, I saw it look on #eql? and
> #hash methods. These two methods are relative to Hash usually, I didn't
> expect methods of Array to depends of them.

It's because the efficient (O(1)) implementation of Array#& requires
creating a temporary hash (or 2?) internally. However, this would seem
to be an internal detail and callers should not have to know about it,
as your example (quoted below) demonstrates.

> A surprising result to me:
>
> irb for ruby-1.9.2-r26764
>> [1,2]&[2]
> => [2]
>> class N
>>   def initialize(n)
>>     @n = n
>>     end
>>   attr_reader :n
>>   def == o
>>     @n == o.n
>>     end
>>   end
> => nil
>> [N.new(1),N.new(2)]&[N.new(2)]
> => [] # instead of [#<N:.. @n=2>]
>