Asp Forum - Can't include a module in Enumerable?

Trans

6/23/2007 6:15:00 PM

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.

7 Answers

Rick DeNatale

6/23/2007 8:34:00 PM

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?

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.denh...

Gregory Brown

6/23/2007 8:47:00 PM

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

Pit Capitain

6/24/2007 8:37:00 AM

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

Robert Dober

6/24/2007 10:28:00 AM

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?
>
> T.
>
>
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
--
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw

Trans

6/24/2007 10:48:00 AM

On Jun 24, 4:37 am, "Pit Capitain" <pit.capit...@gmail.com> wrote:
> 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

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.

Pit Capitain

6/24/2007 12:02:00 PM

2007/6/24, Trans <transfire@gmail.com>:
> 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

Trans

6/24/2007 3:58:00 PM

On Jun 24, 8:01 am, "Pit Capitain" <pit.capit...@gmail.com> wrote:
> 2007/6/24, Trans <transf...@gmail.com>:
>
> > 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.

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.

comp.lang.ruby

Can't include a module in Enumerable?

Trans

Rick DeNatale

Gregory Brown

Pit Capitain

Robert Dober

Trans

Pit Capitain

Trans

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