From: James Edward Gray II <james@...>
Date: 2005-10-01T00:28:35+09:00
Subject: Re: Operator Overloading <<

On Sep 30, 2005, at 9:56 AM, Matt Hulse wrote:

> Are delegates common to all OO languages?  I don't remember learning
> about them in my C++ class.

Delegation is a design pattern and in that sense, yes, it's common to  
most languages:

http://en.wikipedia.org/wiki/Delegation_%28programming%29

In Ruby, we have two standard libraries that cover delegation.  I  
just finished documenting them and am trying to get them up on ruby- 
doc.org, but until then, here's some sample code from the docs of  
delegate.rb:

#
# The primary interface to this library.  Use to setup delegation  
when defining
# your class.
#
#   class MyClass < DelegateClass( ClassToDelegateTo )    # Step 1
#     def initiaize
#       super(obj_of_ClassToDelegateTo)                   # Step 2
#     end
#   end
#

and

#
# === DelegateClass()
#
# Here's a sample of use from <i>tempfile.rb</i>.
#
# A _Tempfile_ object is really just a _File_ object with a few  
special rules
# about storage location and/or when the File should be deleted.   
That makes for
# an almost textbook perfect example of how to use delegation.
#
#   class Tempfile < DelegateClass(File)
#     # constant and class member data initialization...
#
#     def initialize(basename, tmpdir=Dir::tmpdir)
#       # build up file path/name in var tmpname...
#
#       @tmpfile = File.open(tmpname, File::RDWR|File::CREAT| 
File::EXCL, 0600)
#
#       # ...
#
#       super(@tmpfile)
#
#       # below this point, all methods of File are supported...
#     end
#
#     # ...
#   end
#

Hope that helps.

James Edward Gray II