From: Eric Mahurin <eric.mahurin@...>
Date: 2008-02-24T08:27:02+09:00
Subject: Re: Monkeypatching is Destroying Ruby

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On Sat, Feb 23, 2008 at 4:36 PM, Avdi Grimm <avdi@avdi.org> wrote:

> On Sat, Feb 23, 2008 at 5:23 PM, Eric Mahurin <eric.mahurin@gmail.com>
> wrote:
> >  * adding new (or perceived missing) functionality (methods) to a class.
>  The
> >  traditional solution would be to just inherit from the class and use
> the
> >  derived class instead where you want this new functionality.  Since you
> >  can't inherit from some classes (i.e. immediates, a problem with the
> >  language IMHO), you can instead use something like Forwardable instead.
>
> Indeed.  The irony here is that Ruby is perhaps the easiest language
> in the world to implement delegation in.  I'm planning on writing a
> series of posts on alternatives to monkey patching, and delegation is
> going to be one of the first techniques I talk about.
>

Here are the main alternatives I use (in order):

* put the functionality elsewhere.  The simplest example is instead of
monkey-patching String#to_xyz, make XYZ::from_s.  When your new class wants
some interaction with a built-in class, put the functionality in the new
class instead of monkey-patching it into built-in class.  The monkey
patching approach usually just saves you a few characters when using the new
functionality.  I do this 95% of the time where others might monkey-patch.
* inherit the class where you want additional functionality and use the
derived class instead.
* use delegation if inheritance doesn't work (immediates).  Delegation is
basically just a "has-a" implementation of "is-a" (inheritance), but it
gives a little more flexibility.  I've never really had to use this when I
was tempted to monkey-patch.

It would be an interesting exercise to go through some of the ruby stdlib
and show alternatives to monkey-patching.

Eric

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