From: Marc Merlin <mmerlin@...>
Date: 2004-12-30T13:26:44+09:00
Subject: Re: #send and private methods

I find that my sympathies lie with the original poster (Brain Palmer) with
regard to Object#send bypassing conventional access controls, although I do
agree that the rationales presented by the other responders are more than
likely historically accurate.

What I mean is this.  Private access designation, although an artifact of OO
methodology, serves a much broader role.  It is a mechanism for allowing a
programmer to organize his or her implementation while explicitly noting
that certain details of the implementation are subject to change.  It is
way of saying that such details should not be relied upon by clients of the
implementation.  Why?  To put it simply, it is a way of saying "these
things may behave differently or be entirely absent in future releases of
this component."

Although I agree that programming languages should be "enabling" in that
they should promote creative problem-solving and although I agree that
"adult" programmers accept the responsibility of bypassing the constraints
imposed upon them by the structure of the programming languages that they
use, the fact of the matter is that it is not necessarily the creative and
mature programmer who suffers the consequences of having taken such
liberties with access control.  Sadly, other programmers - and ultimately
end users - who rely on the integrity of complex software systems to
continue to function properly in spite of ongoing revision are the ones
likely to be injured when access controls are disregarded.

In other words, information hiding is a way of making software systems
resilient in the face of change.  It is not simply a way "nanny"
programming languages try to keep "top-gun" programmers from getting their
job done.  Of course, for small projects with a restricted user base these
constraints hardly matter.  If Ruby were intended to be only a prototyping
tool, then bypassing access controls would be no big deal.  But Ruby
apparently is on the way to being adopted as a bona fide
progamming-language-in-the-large, as evidenced by such trailblazing
projects as the Rails framework.  (I certainly hope so!)  Consequently I
think that the adherence to a rigorous informtation hiding schema should be
taken seriously and mechanisms to bypass it should be brought into
question.

- Marc Merlin