From: Jamis Buck <jgb3@...>
Date: 2003-12-03T12:53:21+09:00
Subject: Re: What's the best way to create methods dealing with an object	of a certain class?

Lyle Johnson wrote:

> Leif K-Brooks wrote:
>
> > I want to add a method to be run on Strings. Currently, I'm just
> > adding it on to the String class. Should I be subclassing it
> > instead? Creating a method which takes a String as an argument?
>
> I have mixed feelings about re-opening built-in classes (like String)
> to add new methods to them, even though the provision for this is one
> of Ruby's attractions. My concern is that people get used to the
> built-ins and expect certain standard behaviors from them; augmenting
> or otherwise changing them could create confusion for other people
> looking at your code.

I agree with Lyle, but only if you are modifying the behavior of an
existing feature of the class.  For instance, changing the + operator to
do something wierd to a string instead of concatenation is just wrong. 
However, modifying existing classes to augment their behavior by adding
new features is something I find to be very natural.  Just the other day
I wanted a method that would tell me how many initial letters two
strings had in common.  Rather than having a utility method that would
do it, and which would feel very *un*-object-oriented, I added a method
to string and could say:

  prefix_length = string1.prefix_length( string2 )

As Lyle said, though, there is no right or wrong answer here.  I think
it completely depends on personal preference.

- Jamis