From: Logan Capaldo <logancapaldo@...>
Date: 2005-05-30T06:03:01+09:00
Subject: Re: method visibility

On 5/28/05, Bob Aman <vacindak@gmail.com> wrote:
> More nubyness.  Apologies.
> 
> Ok, so, I have this rss feed caching system i'm working on.  Ideally,
> I'd like to have as little of the internal workings of the thing
> visible as possible.  I just want the programmer to interact with Feed
> and FeedItem objects, not the caching mechanisms.
> 
> It seems to me that I don't really want the programmer to be able to
> create instances of a FeedItem manually.  All FeedItems ought to be
> created automatically by a Feed object.  But it seems like ruby lacks
> the direct equivalent of c++'s "friend", so I guess I can't give
> access to the "new" class method only to Feed.
> 
> Also, I'd like to make the caching mechanism be changable.  It'd be
> nice to be able to switch between, say, a database-based cache and a
> file system-based cache.  Perhaps like this:
> 
> FeedCache.cache_type = :DatabaseFeedCache
> 
> And then the Feed object would simply use the DatabaseFeedCache behind
> the scenes.  But again, I'm not sure how to make the cache's behavior
> available only to the Feed and FeedItem classes (or even if I can).
> --
> Bob Aman
> 
> 

You could do one of these:

class A
private_class_method :new
end

class FriendOfA
    def make_an_A
          A.class_eval { new }
    end
end

Of course still doesn't stop anyone from just doing a class_eval
themselves, but it does make it slightly more discouraging, and they
definitely won't do it by accident.