From: David Alan Black <dblack@...>
Date: 2001-03-05T23:42:07+09:00
Subject: [ruby-talk:12019] hooking/wrapping all of a classes methods

Hello --

What I mean is:

Let's say I write an IO-layer class with a bunch of methods that do
something with files.  I want every method to lock and unlock the file
(or at least check that it is locked, or whatever).  I don't feel like
having to remember to write that into every method.

My current thinking is to automatically wrap the insides of the
methods.  Here's an example, where my methods are very simple and the
code to wrap them just adds a couple of puts's.  My question is: how
does this rate as a way to do this?  Pitfalls?  (I sense there might
be some in connection with argument handling, though the few tests
I've done have been OK.)  More concise ways?


  class Thing
    def mone
      puts "hi"
    end

    def mtwo(a)
      puts "bye"
    end

    superclass.instance_methods - instance_methods .each do |m|
      al = "__#{m.id}__"
      alias_method al, m

      module_eval <<-EOE
      def #{m}(*args)
	puts "Entering method #{m}"
	#{al}(*args)
	ensure
	puts "Leaving method #{m}"
      end
      EOE
    end

  end


# Test

  t = Thing.new
  begin
    t.mone
    t.mtwo     # ArgumentError
  rescue ArgumentError => msg
    puts msg
    Thing.new.mtwo(3)  # OK
  end


__END__

=>
  Entering method mone
  hi
  Leaving method mone
  Entering method mtwo
  Leaving method mtwo
  wrong # of arguments(0 for 1)
  Entering method mtwo
  bye
  Leaving method mtwo


Thanks --


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav