Ruby #in method.

in.rb

# in extension to object.
#
class Object
  # Returns true if the object sent #in is included in the argument list.
  #
  # Usage in conditionals:
  #
  #   if 1.in 1, 2, 3
  #     puts "1 was included"
  #   end
  #
  #   if "x".in *xyz
  #     puts "x was included"
  #   end
  #
  #   if color.in :white, :gray, :black
  #     puts "#{color} isn’t a color."
  #   end
  #
  # It can also be used a safe alternative to ==.
  #
  #   if 1.in 1.0
  #     puts "1 == 1.0 #=> true"
  #   end
  #
  # Using in like this avoids accidental assignment, like .eql?, but unlike .eql?
  # has the same semantics as ==, which is often idea. 
  #
  def in(*ary)
    ary.include?(self)
  end
end

"(Am I the only person to have ever thought of this?)"

Nope :-) I like it though!

Oh well... It's sooo sexy.

Hey @maletor @jeyb @smcpherson, what do you guys think?

Here's another implementation using recursion.

class Object
  def in(head, *tail)
    head == self || tail.any? && self.in(*tail)
  end
end

@blakefrost That implementation is probably less efficient, will break if you're searching for nil or false. (See Enumerable#any?)