Re: friend classes in ada95

[Robert Dewar <robert_dewar@my-deja.com>]

In article <38FD1830.949F5E81@mindspring.com>,
  "John J. Rusnak" <john.rusnak@mindspring.com> wrote:

> I'd have to weigh in on the opposite side.  "Class" and
> "object" are rather easy terms to grasp.

A tagged object in Ada is NOT a class in the OO sense, and oddly
this is true of a class in C++. Just because you call something
a class in C++ does not mean you are defining an object or class
in the OO sense.

I find that pretty confusing in C++ I must say, and it
definitely leads people into the realms of mega-confusion.
I often see people who define "classes" in C++ and thinking
they are doing object oriented programming, when they are just
defining abstract data types.

Class and object may be easy terms for you to grasp, but most
C++ programmers seem quite confused if you ask them to define
the difference between an abstract data type and an object.

Tagged types are simply types with particular properties that
are useful for many programming purposes (e.g. one use is to
simply ensure that objects (in the Ada sense!) of the type are
passed by reference, there are many many other uses, including
the fact that tagged types are suitable for representing
certain kinds of objects (in the OO sense).

> And I can tell you through exeperience that the Ada
> model has been difficult for many I have seen coming into the
> language to grasp.

Anyone who understands what types and abstract data types are
about should have no trouble with the Ada type model. If you are
talking about the "object" model of Ada, then my response is
that this is VERY confused thinking.

Object oriented programming is about a paradigm for program
design, it is not a language construct!

  (Some with OO backgrounds and some without).  But to each
their own
> I suppose.
>
> I agree with the comment on "code words", though.
>
> -John
>
> tmoran@bix.com wrote:
>
> > > A tagged type is not a class. A tagged type is a
programming construct
> >   When first trying to understand this stuff, I personally
found thinking
> > of a tag on a record etc to be much easier to understand
than all the
> > OO stuff about classes and objects.  "class" and "object"
are such
> > vague terms they convey little information. Also they are
used for
> > a variety of *different* things (see mathematics, or MS's
use of "class"
> > in COM).  OTOH, if one's intent is to certify membership in
an
> > exclusive club by the use of code words known only to the
members,
> > then "class" is as good as anything.
>
>


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