Modify only a .rb file, but not other .rb files, while still extending core classes?

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.

On Wed, Oct 26, 2011 at 4:04 PM, Marc H. [email protected]
wrote:

.rb file though.

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 = [1,2,3,4,5]
some_elements.extend(Randomizable)
some_elements.rand

All other arrays in the system will not be affected.

Jesus.

2011/10/26 Jesús Gabriel y Galán [email protected]

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).

[email protected]:~$ irb
001:0> a = [1,2,3,4,5]
=> [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
=> nil
007:0> a.rand
=> [4, 1, 5, 3, 2]
008:0> b = [6,7,8,9,10]
=> [6, 7, 8, 9, 10]
009:0> Array.methods.grep(/rand/)
=> []
010:0> a.methods.grep(/rand/)
=> [:rand]
011:0> b.methods.grep(/rand/)
=> []

HTH,

Peter

On Wed, Oct 26, 2011 at 4:28 PM, Peter V.
[email protected] wrote:

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).

Sure, but if you need it in several arrays, the module approach is
cleaner.
And I’d say that even for one array is cleaner too :).

Jesus.

On Wed, Oct 26, 2011 at 9:04 AM, Marc H. [email protected]
wrote:

.rb file though.

rand(array)

So I would prefer to be able to do only the array.rand.


Posted via http://www.ruby-forum.com/.

Things like that will be available in Ruby 2.0, but aren’t available yet
(
http://yehudakatz.com/2010/11/30/ruby-2-0-refinements-in-practice/)

2011/10/26 Jess Gabriel y Galn [email protected]:

On Wed, Oct 26, 2011 at 4:28 PM, Peter V.
[email protected] wrote:

2011/10/26 Jess Gabriel y Galn [email protected]

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

Sure, but if you need it in several arrays, the module approach is cleaner.
And I’d say that even for one array is cleaner too :).

Not only that: I’d expect it to use less resources, too. Reason is
that there is just one definition of the method. Plus, it’s easier to
later change it for all Array instances if that should be needed.

Marc, we do not know what your method #rand does and which Ruby
version you are using, but since 1.9 there is Array#sample which might
be exactly what you are looking for.

Kind regards

robert

2011/10/26 Jesús Gabriel y Galán [email protected]

One solution would be to create a module with the rand method, and
some_elements = [1,2,3,4,5]
(what extend is doing in your implementation).

Sure, but if you need it in several arrays, the module approach is cleaner.
And I’d say that even for one array is cleaner too :).

Agreed.

I just thought that maybe it was easier to understand the concept of a
singleton
class of an object in isolation “change only the behavior of this
instance,
not
of the class or of other instances of the class”, without adding the
difference
between Module include and extend into the example.

HTH,

Peter

On an unrelated note, if you want a random element from an array,
there’s already a method for that, Array#sample. (or #choice in
1.8.7).

– Matma R.

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