From: Peter Vandenabeele <peter@...>
Date: 2011-10-26T23:28:06+09:00
Subject: Re: Modify only a .rb file, but not other .rb files, while still extending core classes?

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2011/10/26 Jes=C3=BAs Gabriel y Gal=C3=A1n <jgabrielygalan@gmail.com>

> On Wed, Oct 26, 2011 at 4:04 PM, Marc Heiler <shevegen@linuxmail.org>
> wrote:
> > Given is a small .rb file.
> >
> > In that .rb file, class Array is modified and a convenience
> > method is added.
> >
> > class Array
> >
> >  def rand
> >
> > I want to limit this modification to only that specific
> > .rb file though.
> >
> > When I use that .rb file in a larger project, I do not want
> > the modification of class Array to leak out into other .rb
> > files. Is there a way to limit the scope of the modification?
> >
> > Of course I can define a method simply and call that, but:
> >
> >  array.rand
> >
> > Looks better to my eyes than:
> >
> >  rand(array)
> >
> > So I would prefer to be able to do only the array.rand.
>
> One solution would be to create a module with the rand method, and
> extend only the arrays you use in that .rb:
>
> # small.rb
>
> module Randomizable
>  def rand
>     # your implentation
>  end
> end
>
> some_elements =3D [1,2,3,4,5]
> some_elements.extend(Randomizable)
> some_elements.rand
>
> All other arrays in the system will not be affected.
>
> Jesus.
>


I think an equivalent way is to directly open the singleton class of a
(what extend is doing in your implementation).

peterv@ASUS:~$ irb
001:0> a =3D [1,2,3,4,5]
=3D> [1, 2, 3, 4, 5]
002:0> class << a
003:1> def rand
004:2> self.sort_by!{|e| Kernel.rand} # without the Kernel reference,
infinite loop is created
005:2> end
006:1> end
=3D> nil
007:0> a.rand
=3D> [4, 1, 5, 3, 2]
008:0> b =3D [6,7,8,9,10]
=3D> [6, 7, 8, 9, 10]
009:0> Array.methods.grep(/rand/)
=3D> []
010:0> a.methods.grep(/rand/)
=3D> [:rand]
011:0> b.methods.grep(/rand/)
=3D> []

HTH,

Peter

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