From: Gregory Brown <gregory.t.brown@...>
Date: 2007-06-24T05:46:49+09:00
Subject: Re: Can't include a module in Enumerable?

On 6/23/07, Trans <transfire@gmail.com> wrote:
> irb(main):002:1> module Z
> irb(main):003:1>   def x; "x"; end
> irb(main):004:1> end
> => nil
> irb(main):005:0> module Enumerable
> irb(main):006:1>   include Z
> irb(main):007:1> end
> => Enumerable
> irb(main):008:0> a = [1,2,3,4,5]
> => [1, 2, 3, 4, 5]
> irb(main):009:0> a.x
> NoMethodError: undefined method `x' for [1, 2, 3, 4, 5]:Array
>         from (irb):9
>         from :0
>
> Is the Double Inclusion Problem worse than I realized? I thought the
> above would be okay b/c 'a' is instantiated _after_ the inclusion
> (which is why I've often called it the Dynamic Inclusion Problem).
> What gives?

Rick answered this, but maybe this is a solution for what you're trying to do:

>> module ZEnumerable
>>   include Enumerable
>>   def x; "x"; end
>> end

>> class B
>>   include ZEnumerable
>>
?>   def each
>>     [1,2,3].each { |e| yield(e) }
>>   end
>> end

>> class Array
>>   include ZEnumerable
>> end
=> Array
>> [1,2,3].x
=> "x"
>> B.new.map { |e| e + 1 }
=> [2, 3, 4]
>> B.new.x
=> "x"

Yeah, you'd need to go remix existing enumerable classes, but it keeps
you from having to do the additional include for *new* objects