Hi --

On Fri, 20 Jan 2006, Thomas Snide wrote:

> Can someone clarify the difference between declaring a method Protected
> vs. Private?
>
> I thought that a private method could only be accessed within the
> specific defining class.  However, it may also be called by subclasses.
> So why the need for protected?

A private method can only be called with no explicit receiver.  That
means that the receiver has to be "self" -- because that's the only
time there can be no explicit receiver.  (Private methods ending in
"=" do allow an explicit receiver, because they have to so that they
won't be parsed as variable assignments.)

What protected does is to let you call a method *with* an explicit
receiver, as long as that receiver is of the same class is "self".

That means you can do things like:

   def compare_with(other)
     self.x <=> other.x
   end

even if x is protected, whereas you can't do that from the outside
(without instance_eval or some other "invasive" technique).


David

-- 
David A. Black
dblack / wobblini.net

"Ruby for Rails", from Manning Publications, coming April 2006!
http://www.manning.com/books/black