Re: friend classes in ada95

[Jon S Anthony <jsa@synquiry.com>]

Charles Hixson wrote:

> My original definition of an Object (I was coming to C++ from C
> after being exposed to Apple's Object Pascal) was: An object is a
> data structure combined with the methods defined to access it.  It
> is made useful by inheritance.

Or true delegation (you don't need to have class based "oo" to have
"oo", ;-)


> I still think that this is the "basic" definition in most languages,
> however Ada and Lisp parse the world very differently.  In their
> view, the methods are NOT a part of the object.

They are just being more "honest" - the methods are not part of the
object in nearly any of these other languages either.  About the only
exceptions to this are some CL based methods-per-object object systems
and Object Logo.

Note that building a standard simple "distinguished object" version of
OO in CL is about 4 or 5 pages of code.  Complete with standard
module/class conflation, er constructs, method definition, etc.  Even
includes MI.


>  So we are left with Tagged ADT's which are made useful

In Ada.

In CLOS you have: generic functions and true multiple dispatch (+ the
MOP, with which you can decide your own method dispatch protocol if
need be).


> through inheritance.  Personally, I think that it makes a reasonable
> amount of sense to chunk the methods with the object, but I'm not
> vehement on the point,

It is the naive and simplistic way.  It is also rather limited (and
limiting) and a poor way if you really are interested in creating
highly expressive systems, i.e., solving problems and not just
interested in towing the standard simplistic OO line.

Frankly, the standard OO line is highly overrated and rather boring.


/Jon

-- 
Jon Anthony
Synquiry Technologies, Ltd. Belmont, MA 02478, 617.484.3383
"Nightmares - Ha!  The way my life's been going lately,
 Who'd notice?"  -- Londo Mollari