method_logging.rb

# Totally untested.

module MethodLogging
  def self.included(base)
    base.methods.each do |m|
      alias_method :"old_#{m}", m
      define_method(m) do |args|
        puts "Called #{m}(#{args.map{|a|a.inspect}.join(', ')})"
        return_value = send("old_#{m}", *args)
        puts "# => #{return_value.inspect}"
        return_value
      end
    end
  end
end

class Foo
  def bar
    # ...
  end

  include MethodLogging
end