From: Caleb Clausen <vikkous@...>
Date: 2007-04-23T23:43:42+09:00
Subject: Re: Arrow operator with dash instead of equals (->)

It's not possible to define a -> operator in Ruby, but you can
(sometimes) define <-. Watch:

class Right
  def -@
     return Negated.new(self)
  end

  class Negated
     def initialize(right)
        @inner=right
     end

     attr :inner
  end
end

class Left
  def <(negated_right)
     self.inspect + " <- " + negated_right.inner.inspect
  end
end

Left.new <- Right.new   #=> "#<Left:0x403cf68c> <- #<Right:0x403cf678>"

It's actually two operators, so there's a caveat: if the right-side
class already defines unary minus, this won't work.

(I first read about this trick in a C++ book. I'm not necessarily
recommending it.)