From: David Alan Black <dblack@...>
Date: 2002-04-21T20:38:37+09:00
Subject: Re: problem with alias

Hi --

On Sun, 21 Apr 2002, Guy N. Hurst wrote:

> I just discovered a problem with how alias works while
> testing some code in irb.
>
> It is common in ruby to alias a method you are about to
> override so you can still access the original functionality.
> However, if that portion of code is executed more than
> once (such as being included or evaluated more than once),
> then the original method gets lost.
>
> In short,
>
> alias old_meth meth
> alias old_meth meth
>
> will result in meth being lost forever.

[...]

> Perhaps a companion to #send would work, such as #send_original ?
> Yet, I suppose someone could override *that* and cause problems.
> So it really does point to the possible need for a new keyword, if
> not an alteration to the existing functionality of alias. Perhaps
> adding a third parameter indicating whether the original or existing
> method should be aliased?
>
> alias old_sf % true   # true means use original
> alias old_meth meth false  # false means don't use original; this is default
> alias old_meth meth   # same as using false for third param
>
> Comments?

I'm not sure the concept of an "original" definition is an exact fit
for the problem.  You might not always know what the first definition
of something was, and/or the one you want to revert to might be an
interim definition.

For instance -- a very contrived example, but anyway -- let's say you
write this:

  # thing.rb
  class Thing
    def action
      puts "original definition"
    end

    alias :oldaction :action true

    def action
      puts "second definition"
      puts "I used to do this: "
      oldaction
    end
  end

and then someone else writes this:

  class Thing
    def action
      puts "sneaky pre-original definition"
    end
  end

  require 'thing'


(Hey, I *said* it was contrived :-)


David

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