gistfile1.rb

#!/usr/bin/env ruby

def register(object = nil, &block)
  obj = block_given? ? block : object
  obj.call if obj.respond_to?(:call)
end

class MyClass
  def call
    puts "three"
  end
end

register proc { puts "one" }
register { puts "two" }
register MyClass.new
register "foo" # fail silently

# one
# two
# three