From: Avi Bryant <avi@...4.com>
Date: 2001-03-05T23:55:36+09:00
Subject: [ruby-talk:12021] Re: hooking/wrapping all of a classes methods


David -

have a look at http://beta4.com/advice.c - it allows exactly what you're
talking about, a little bit cleaner.

For a more general solution, look at AspectR in the RAA.

On Mon, 5 Mar 2001, David Alan Black wrote:

> 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
>