From: Denis Leclair <lists@...>
Date: 2012-08-19T00:10:43+09:00
Subject: accessing protected or private methods from class methods

There is all kinds of information out there on Ruby method visibility
rules. After doing a lot of reading I think I have pretty good handle on
how the rules work but what I'm still struggling with is the philosophy.

Let me clarify where I'm having difficulty with a specific example...

There are times when I want to setup a class interface in such a way
that the normal instantiation method (new() method in most languages)
cannot
be used and to force the caller to use a class (a.k.a. static) factory
method so that certain decisions can be made prior to object creation.

After a lot of trial and error, and reading on the subject, I've reached
the conclusion that this pattern cannot be done cleanly in Ruby. The
fundamental problem seems to be that as soon as the new() method is made
private then not only is it restricted from the
public API, but it's also blocked from being called from the class' own
factory method. The only way I can see to circumvent the restriction is
to use the ugly .send() method to bypass visibility rules.

The code snippet (http://snipt.org/vAk4) shows how I've implemented this
in Ruby, but again, it just seems wrong that I have to bypass the
visibility rules using the .send() method.

Can anybody clarify the rationale for the restrictions placed on class
methods and/or if there is a better way to implement this common pattern
in Ruby?

Thanks,
Denis

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