From: Robert Feldt <feldt@...>
Date: 2001-11-03T01:49:05+09:00
Subject: [ruby-talk:24177] A short, pure-Ruby AOP implementation

Hi,

Couldn't help posting this; its getting late in Sweden and its time to go
home... ;-)

Have a nice weekend!

/R

# Friday-late AOP puzzle: Is this the shortest possible pure-Ruby, 
# call-level AOP implementation?
# I'm sure there are many problems with it but its < 30 LOC!

class Aerial
  def initialize(object)
    @object = object
  end

  # Undefine methods so that we can relay them to the real object
  # Is it really dangerous to undef __id__ and __send__? What can
happen?
  Object.new.methods.each {|m| undef_method(m.intern) unless m =~ /__/}

  def __pre_all__; end
  def __post_all__; end
  def __around_all__; yield; end

  def method_missing(methodId, *args, &b)
    @__result__ = @__exit_status__ = nil
    __around_all__ {
      __pre_all__(methodId, *args)
      begin
	@__result__ = @object.send(methodId, *args, &b)
      rescue Exception => @__exit_status__
      end
      __post_all__(methodId, *args, &b)
    }
    raise @__exit_status__ if @__exit_status__
    @__result__
  end
end

if __FILE__ == $0
  class Tracer < Aerial
    def __pre_all__(methodId, *args, &b)
      print
"#{@object.send(:type).inspect}##{methodId.id2name}(#{args.map{|e|
e.inspect}.join(', ')})"
    end

    def __post_all__(methodId, *args, &b)
      if @__exit_status__
	puts " raised an exception #{@__exit_status__.inspect}"
      else
	puts " = #{@__result__.inspect}"
      end
    end
  end

  t, sum = Tracer.new(Array.new), 0
  t.push 1
  t.length
  t.each {|e| sum += e}
  p sum                  # And it works with blocks!
  begin
    t.dummy
  rescue
  end
  t.pop
end