From: Simon Strandgaard <qj5nd7l02@...>
Date: 2003-11-18T07:47:17+09:00
Subject: Re: Yet Another Rite Thought: method combination

On Mon, 17 Nov 2003 07:22:01 +0000, gabriele renzi wrote:

> I just looked at matz' slides and I don't have a clear understanding
> of ho9w this is suposed to work.
> 
> Possibly this has been explained verbosely, But I can't get it from
> the slide.
> 
> So, this is the example:
> 
> class Foo
>  def foo(*args)       #1
>    p 'foo'
>  end
>  def foo:pre (*args ) #2
>   p 'pre'
>  end
> end

How about something like ?

This is only a partial example.. I have no clue how to do it with proc's.
But there should be a convertion from yield-block to proc.

server> ruby a.rb
before #test
42
after #test
server> expand -t2 a.rb 
class Object
  def self.def_pre(*args)
    args.each{|symbol| 
      begin
        meth = instance_method(symbol)
      rescue => e
        $stderr.puts "ERROR: symbol2method failure, " + e.inspect
        next
      end  
      name = symbol.id2name
      org = "_defpre_"+name
      arguments = (meth.arity != 0) ? "(*a,&b)" : "(&b)"
      module_eval <<MSG
      alias #{org} #{name}
      def #{name}#{arguments}
        $stdout.puts("before ##{name}")
        #{org}#{arguments}
        $stdout.puts("after ##{name}") 
      ensure
        $debug = nil
      end
      private :#{org}
MSG
    }
  end
end

class A
  def test; p 42 end
end

class B < A
  def_pre :test #{ puts "pre" }
end

B.new.test
server> 


--
Simon Strandgaard