From: Henrik Horneber <ryco@...>
Date: 2004-10-06T03:29:35+09:00
Subject: Extending existing classes (was: Re: A ruby course)

Hi!

Taking over from Brian (sorry :) ) I need to ask a question of my own.


Brian Schr�der wrote:

> Henrik Horneber wrote:
....
>> - extending String so you can tell it to remove cpp comments /* remove 
>> me */
>>
>> Of course both tasks could be accomplished without extending those 
>> classes. I have no idea in which cases you should write helper methods 
>> and when you should extend existing classes... does anybody have some 
>> 'heuristics' or best practices?
>>
>> regards,
>> Henrik
>>
> 
> Hello Henrik,
> 
....
> 
> Extending string with something like remove_cpp_comments seems awkward 
> to me. In any usecase for this I'd rather have a class CppCode that I 
> can ask to remove_comments. (Or even better, to give me the source 
> without comments.)
> 
> So my personal heuristic tells me not to extend in this case.

Now, the reason I was immediatly reminded of that remove_cpp_comments 
example is, that I wrote a small script some time ago, which used 
exactly this case. First, I implemented remove_cpp_comments in its own 
class (which was not called CppCode, but had the same intend), but out 
of curiosity (and because in ruby I can, dang it! :) ) I moved the 
remove_cpp_comments method to String. Turns out, the method got shorter 
  and somewhat clearer, at least to me. And I could write something like

source_code = IO.readlines(file).join("\n")        	
source_code.strip_comments!
# instead of source_code = CppCode.strip_comments( source_code)	


.... you get the idea.

Even though the code became clearer on that level, I still have to agree 
with Brian that it is somehow dirty/awkward on a different level to 
extend String with such a method.

This, formerly extremly happy, Ruby user is confused.

What are your experiences?

regards,

Henrik