It's not a problem in Ruby because you don't pass around method instances, you pass around Procs (wrapped blocks, lambdas and procs), so if you are passing a callable around, you know it's a Proc. If you are passing around a method instance, you should almost certainly be using a block, lambda or proc.

Also, see wycats post: http://yehudakatz.com/2010/02/21/ruby-is-not-a-callable-orie...