Following a discussion on ruby-talk of a few ideas for ruby[1],
thought I'd suggest them (one at a time) to core.
Here's the first.

Add an Object#in? method to complement Enumerable#include?

Background: currently if you want to test for membership you have to
do it "backward" by using include? on the array.

ex:

if STUFF.include?(a)
 puts 'yes'
else
 puts 'no'
end

Clearer to the reader (at least to my eyes) would be

if a.in?(STUFF)
 puts 'yes'
else
 puts 'no'
end

proposed definition (from [3])

module Kernel
  # Is self included in other?
  #
  #   5.in?(0..10)       #=> true
  #   5.in?([0,1,2,3])   #=> false
  #
  def in?(other)
    other.include?(self)
  end

end

currently several developers said they use this idiom already [1,2,3],
facets has it, and I have found it quite useful in the past, therefore
propose its incorporation into core.

drawbacks: existing 'in?' methods would become ambiguous--I'd imagine
this is rare so hopefully a limited impact.

Thoughts?
Thanks.
-=r

[1] http://www.ruby-forum.com/topic/184011
[2] http://snippets.dzone.com/posts/show/3516
[3] http://facets.rubyforge.org/doc/api/core/classes/Kernel.html#M000425