# Can't include a module in Enumerable? **URL:** \ **Category:** Ruby\ **Created:** [June 23, 2007, 8:49pm UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595 "2007-06-23T20:49:35Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Trans](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@Trans](https://www.ruby-forum.com/u/Trans)\ **Post date:** [June 23, 2007, 8:49pm UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595/1 "2007-06-23T20:49:35Z")
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? T. ---
**Author:** ![Trans](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@Trans](https://www.ruby-forum.com/u/Trans)\ **Post date:** [June 23, 2007, 10:34pm UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595/2 "2007-06-23T22:34:49Z")
On 6/23/07, Trans [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 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? It’s not the instance, it’s the class Array, and that existed (and included Enumerable) before you changed Enumerable. – Rick DeNatale My blog on Ruby [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![Trans](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@Trans](https://www.ruby-forum.com/u/Trans)\ **Post date:** [June 23, 2007, 10:47pm UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595/3 "2007-06-23T22:47:49Z")
On 6/23/07, Trans [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 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 ---
**Author:** ![Trans](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@Trans](https://www.ruby-forum.com/u/Trans)\ **Post date:** [June 24, 2007, 10:38am UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595/4 "2007-06-24T10:38:35Z")
Tom, here’s something to experiment with. I haven’t tested it extensively: class Module alias :old\_include :include def include other old\_include other if self.class == Module this = self ObjectSpace.each\_object Module do |mod| mod.module\_eval do include this end if mod \< self end end end end module Z def x; “x”; end end module Enumerable include Z end a = [1,2,3,4,5] p a.x # =\> “x” Regards, Pit ---
**Author:** ![Trans](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@Trans](https://www.ruby-forum.com/u/Trans)\ **Post date:** [June 24, 2007, 12:28pm UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595/5 "2007-06-24T12:28:45Z")
On 6/23/07, Trans [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > irb(main):009:0\> a.x Just reinclude Enumerable, well that seems to be the simplest way to achieve what you wanted: > 510/10 \> irb irb(main):001:0\> module A; def x; 42 end end =\> nil irb(main):002:0\> module Enumerable; include A end =\> Enumerable irb(main):003:0\> class Array; include Enumerable end =\> Array irb(main):004:0\> [].x =\> 42 And yes it works outside irb too. Robert ---
**Author:** ![Trans](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@Trans](https://www.ruby-forum.com/u/Trans)\ **Post date:** [June 24, 2007, 12:48pm UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595/6 "2007-06-24T12:48:46Z")
On Jun 24, 4:37 am, “Pit C.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ``` > end > > ``` > > end > > a = [1,2,3,4,5] > p a.x # =\> “x” > > Regards, > Pit Pit Smack Down! You go and solve the Double Inclusion Problem just like that!? There must be a large issue. Why wouldn’t Matz have already pursued this? Granted, I see a little inefficiency, but nothing an Observer pattern couldn’t mitigate. What say you? I’m Speechless. T. ---
**Author:** ![Trans](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@Trans](https://www.ruby-forum.com/u/Trans)\ **Post date:** [June 24, 2007, 5:58pm UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595/7 "2007-06-24T17:58:21Z")
On Jun 24, 8:01 am, “Pit C.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Tom, thanks for the kind words, but it’s really not so hard to find > just one solution to this problem. I can’t speak for Matz, but I think > he’s looking for a more efficient solution that doesn’t require a lot > of bookkeeping. Okay, I’m being a bit hyperbolic. But you deserve it anyway. I was surprised to see a solution thrown up in a few lines of code. The impression I had developed over previous discourse was such a thing was not readily possible. Of course, now it seems obvious. I knew we could just re-include the module, I just never put two and two together. T. ---
**Author:** ![Trans](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@Trans](https://www.ruby-forum.com/u/Trans)\ **Post date:** [June 24, 2007, 2:02pm UTC](https://www.ruby-forum.com/t/cant-include-a-module-in-enumerable/107595/8 "2007-06-24T14:02:51Z")
2007/6/24, Trans [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > Pit Smack Down! You go and solve the Double Inclusion Problem just > like that!? > > There must be a large issue. Why wouldn’t Matz have already pursued > this? Granted, I see a little inefficiency, but nothing an Observer > pattern couldn’t mitigate. What say you? > > I’m Speechless. Tom, thanks for the kind words, but it’s really not so hard to find just one solution to this problem. I can’t speak for Matz, but I think he’s looking for a more efficient solution that doesn’t require a lot of bookkeeping. Regards, Pit