intercepting ruby method calls to log or add debug behaviour

gistfile1.rb

# idea and much of the implementation from http://stackoverflow.com/questions/2135874/cross-cutting-logging-in-ruby
# e.g. o.class.add_logging :method
# IMPROVE would be very nice if instructions to add logging could be scoped.
class Module

  def add_logging(*method_names)
    method_names.each do |method_name|
      original_method = instance_method(method_name)
      define_method(method_name) do |*args,&blk|
        puts "logging #{method_name}: #{args}"
        original_method.bind(self).call(*args,&blk)
      end
    end
  end

  # TODO unintercept method
  # TODO consider using glue or AspectR
  # TODO find out why this often results in a crash in MacRuby
  def add_intercept(method_name, intercept_action = nil)
    original_method = instance_method(method_name)

    if intercept_action
      define_method(:handle_intercept) do |*args,&blk|
        self.instance_exec(*args, blk, &intercept_action)
      end
    end

    begin
      handler_method = instance_method(:handle_intercept)
    rescue Exception => e
      raise "#{e}: probably no proc passed in, no handle_intercept(*args) method defined."
    end

    define_method(method_name) do |*args,&blk|
      puts "begin intercept of #{method_name} on instance #{self.object_id}"

      begin
        handler_method.bind(self).call(*args, &blk)
      rescue Exception => err
        puts "Error while performing intercept action: #{err}"
      end
      puts "end intercept of #{method_name}"
      original_method.bind(self).call(*args,&blk)
    end
  end
end