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Inherit, Delegate, or Forwarding?

netghost

1/5/2006 6:10:00 PM

When do you guys choose to inherit from a class, use a delegate, or
forwarding?
What are some examples of common uses for Delegates or Forwardable?

I have these fuzzy notions of times they may be useful, but some common
examples would be nice.

Any thought?
.adam


For reference:
[Forwardable]
http://ruby-doc.org/stdlib/libdoc/forwardable/rdoc/...
[Delegate] http://ruby-doc.org/stdlib/libdoc/delegate/rdoc/...
2 Answers

James Gray

1/5/2006 10:23:00 PM

0

On Jan 5, 2006, at 12:12 PM, Adam Sanderson wrote:

> When do you guys choose to inherit from a class, use a delegate, or
> forwarding?

As the saying goes, "Favor composition over inheritance." The theory
there is simply that inheritance is a tighter coupling than
composition, so the latter handles change better. Delegation is a
form of composition.

Any Design Patterns book will have a detailed treatment of this very
topic.

> What are some examples of common uses for Delegates or Forwardable?

Well, I wrote the documentation for both, and I must confess that I
still rarely use Delegate. It can think of one example where I
wanted full delegation and I wanted it for two classes, so I had to
roll my own anyway. The best example I can think of for it is
TempFile[1], in the standard library.

I use forwardable all the time, on the other hand. I love that
library. It allows me to control what gets delegated and rename
delegated methods. Good stuff. Two examples from my work would be
my solution-in-progress to the Ruby Test First Challenge[2] and my
FasterCSV library[3].

Hope that helps.

1: http://stonecode.org:3000/article...
2: http://groups.google.com/group/Ruby-Test-First-Chal...
1df37a6f0b781a88
3: http://rubyforge.org/plugins/scmsvn/viewcvs.php/...
faster_csv.rb?root=fastercsv&view=markup

James Edward Gray II

Berger, Daniel

1/5/2006 10:58:00 PM

0

James Edward Gray II wrote:

> I use forwardable all the time, on the other hand. I love that
> library. It allows me to control what gets delegated and rename
> delegated methods. Good stuff. Two examples from my work would be my
> solution-in-progress to the Ruby Test First Challenge[2] and my
> FasterCSV library[3].

Note that, with some help, I revamped forwardable.rb and it has been
tentatively accepted by Matz for 2.0. The current version has lots of warning
spewage.

http://rubyforge.org/tracker/index.php?func=detail&aid=1923&group_id=426&...

Regards,

Dan