From: Michael Neumann <neumann@...>
Date: 2001-10-24T05:25:19+09:00
Subject: [ruby-talk:23083] Re: Deprecate keyword? (what does 'module_eval <<END' mean?)

Phil Tomson wrote:
> In article <3BD58DB4.2090404@emn.fr>,
> Pierre-Charles David  <Pierre-Charles.David@emn.fr> wrote:
> >Morris, Chris wrote:
> 
> I was looking through your code snippet and there is an idiom that I don't 
> understand, so I thought I'd ask and maybe learn something...
> >
> >----------------------------------------------------
> >class Module
> >   def deprecate(methodName)
> 
> What does this following line mean/do?
> >     module_eval <<END
> >     alias_method :deprecated_#{methodName}, :#{methodName}
> >     def #{methodName}(*args)
> >       $stderr.puts "Warning: calling deprecated method 
> >#{self}.#{methodName}"
> >       return deprecated_#{methodName}(*args)
> >     end
> >END


"<<END" is a here-document string. It is the String to the next "END"
starting on a next line.

"module_eval" evaluates it's first paramter (a string - in our case the here
document) in the module's context.

Above, the module_eval creates an alias to the current definition to
method "methodName". Then it overwrites the method "methodName" with
a new definition. This new definiton outputs at first a warning message
before it calls the original implementation of the method (the alias to
the original definition).

Regards,

  Michael

-- 
Michael Neumann
merlin.zwo InfoDesign GmbH
http://www.merlin-zwo.de