Question

I wrote code for an Enumerables module:

module Enumerables
  def palindrome?
    if self.is_a?(Hash)
      return false
    else
      self.join('').gsub(/\W/,"").downcase == self.join('').gsub(/\W/,"").downcase.reverse
    end
  end
end

The problem is, I have to write these:

class Array
  include Enumerables
end

class Hash
  include Enumerables
end

to make the code run successfully.

Is there an easy way to make the “palindrome?” method run with different instance types?

Answer 1

You could use the ObjectSpace.each_object iterator with a filter to find classes that include Enumerable and extend them dynamically:

# XXX: this iterator yields *every* object in the interpreter!
ObjectSpace.each_object do |obj|
  if obj.is_a?(Class) && (obj < Enumerable)
    obj.module_eval { include Enumerables }
  end
end

[1,2,1].palindrome? # => true
{}.palindrome? # => false

Now the trick is to write something that works for all enumerable types in a meaningful way! Note also that this sort of metaprogramming is fun for kicks but has serious implications if you plan to use it for anything other than “toy” programs.