From: Jim Weirich <jim@...>
Date: 2006-06-06T20:59:24+09:00
Subject: Re: Ruby and the Open-Closed Principle

Jeff Cohen wrote:
> For most of my OO career (C++ for a long time, and then C#) I believed 
> in the OCP very strongly.  It's supposedly the cornerstone of OOP, 
> right?  I came across this article today which brought it mind again: 
> http://www.ddj.com/blog/architectblog/archives/2006/05/open_closed_pri_1.html?cid=GS_blog_arnon
> 
> But I remember my mind getting warped for a few hours when I was first 
> learning Ruby last year and came across Rails code that extended 
> existing classes so you could do this:
> 
> 20.minutes.ago
> 
> which I thought was just awesome.  Ruby lets me change anything I want 
> about any class, it seemed, and it was a strange thing to me.
> 
> Of course, I'm not worried about breaking existing code when it's just 
> my own code, but I'm still violating the open closed principle by 
> changing the Time class, right?  But I think this ability is one of the 
> things that makes Ruby so great!

But isn't this the essence of OCP?  The ability to extend a class (open 
for extensions) without modifying the original code? (which remains 
closed).

-- Jim Weirich

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