Re: abstraction and encapsulation (Re: Will Java kill C++?)

[Richard Riehle <rriehle@nunic.nu.edu>]

On Wed, 15 May 1996, John English wrote:

> Extensibility is important for maintenance too; a lot of maintenance
> changes involve adding extra bells and whistles which can be a major
> problem if extensibility *wasn't* designed for.  This (IMHO) is a
> much more important consideration than reuse, ...

  Exactly.

  As a software product ages, more of the maintenance (Meyer cites a
  study showing 42%) is devoted to extending that product with new
  features than any other single activity.  In conversations with
  other developers, and based on personal experience, I believe
  that maintenance of a mature software product is closer to
  75% to 80% new features.

  The important thing is to add these new features without breaking
  the existing product. Before OOP, this was the equivalent of
  open-heart surgery, and the mortality rate of the software was
  about the same as one expects from such surgery.

  How do we extend an existing product without breaking it. Inheritance
  is one mechanism.  It is not enough, but it is important. Ada 95
  provides some additional mechanisms, as does Eiffel.  C++ is a little
  frail in this regard, but it is better than what we have had in the
  past.  The reality is that we are a long way off from fully satisfying
  the demands of extensibility.  Yet this is where the long-term
  economic benefits are hidden.

  Richard Riehle