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Some of us at Apple have experience in implementing object-oriented systems
and seeing how people learn them.  A few of us implemented an
object-oriented application framework called MacApp, which people have been
using for about 2 years.  Users of MacApp are generally experienced
programmers who have little or no experience with object-oriented
programming.

There is some variation in how quickly people learn object-oriented
programming, and how effectively they apply it.  It seems to take a while
before people understand the concepts of objects, inheritance, and dynamic
binding (message passing).  Usually they flounder for a period of time (a
couple of weeks) until the concepts start making sense.  

After this point, they can start using object-oriented programming, but it
seems to take a few more weeks before they fully understand how to use
object-oriented programming in their application design.   In particular,
there is a distinction between defining an object type that serves a
particular purpose and defining an abstract object that can then be used in
many different ways without having to reimplement it each time.

I think learning an object-oriented language requires changing your
perspective on programming.  (This is especially true when using MacApp,
because most of the control structure of your application is implemented for
you.)  Some people can adapt to this change more quickly than others.

Part of the problem has been that there was no way to experiment with
object-oriented programming until a couple of years ago.  Now you can get
versions of Smalltalk on MS-DOS machines or the Macintosh, you can get C++
on a variety of machines, and you can get Object Pascal on the Macintosh.

Until these things came out, object-oriented programming was something you
could only discuss.  (I took a comparative programming languages class at
MIT several years ago, and the class on Smalltalk consisted of watching a
videotape of someone at Xerox using Smalltalk.)

-- 
Larry Rosenstein

Object Specialist
Apple Computer

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