Abstract Class

[Merlin]

Hi

Been reading the GOF book and started to make the distinction between
Class and Interface inheritance. One question though:

Do pure abstract classes have representations ? (data members?)
What about abstract classes?

Should abstract classes have a destructor and or constructor? What
about pure abstract classes?

What are the conditions that must be satisfied for a class to be

A) Pure Abstract class
B) Abstract Class

Regards

Merlin

[Claudio Puviani]

"David White" <[e-mail] ded> wrote

They might be homework, but now I'm curious. Abstract classes I know, but
"pure abstract classes" I haven't come across. I would have guessed that
"pure" somehow came across from "pure virtual" and is redundant or
inappropriate. Or is a "pure abstract class" one that contains nothing but
an interface of pure virtuals? If so, "pure abstract" sounds more like an OO
term than a C++ term.

You can have pure virtual functions and you can have abstract base classes. You
can't have pure abstract classes. That's just someone mingling unrelated
concepts. Those who do are usually trying to attach a name to a class that has
only pure virtual functions. This, of course, is clearly impossible because every
class must have at least one constructor -- either explicitly or implicitly
defined -- if it's to be instantiated or inherited from and constructors cannot
be virtual. Some add to this fabricated definition that the so-called "pure
abstract class" can have no data members. Others try to call it an interface.
Since these terms are bogus to start with in the context of C++, it's really
irrelevant what rules anyone tries to impose on them. :-)

This is actually symptomatic of something that we see fairly often: some people
are uncomfortable with the vast number of combinations that C++ offers and try to
label and compartmentaliz e specific combinations. Once an arbitrary combination
has been named, these people feel more secure in criticizing code that falls
outside their little subset of absorbed concepts by saying things like, "You're
doing that wrong. You should be using a pure virtual abstract ethereal diaphanous
base class as described in the 'Horde of Sixty-Two' book."

Claudio Puviani

[Jeff Schwab]

Julie wrote:

Victor Bazarov wrote:

Merlin wrote:

Been reading the GOF book and started to make the distinction between
Class and Interface inheritance. One question though:

One? Really?

Do pure abstract classes have representations ? (data members?)

Some do, some don't. Up to you.

What about abstract classes?

What about them?

Should abstract classes have a destructor and or constructor? What
about pure abstract classes?

They should when needed.

What are the conditions that must be satisfied for a class to be

A) Pure Abstract class
B) Abstract Class

Homework questions should be answered by reading your textbook.

What is the purpose of such senseless non-responses and blind assumptions?

Victor answered the meaningful questions correctly and concisely.

[jeffc]

"David White" <[e-mail] ded> wrote in message
news:Dm******** ************@na sal.pacific.net .au...

They might be homework, but now I'm curious. Abstract classes I know, but
"pure abstract classes" I haven't come across. I would have guessed that
"pure" somehow came across from "pure virtual" and is redundant or
inappropriate. Or is a "pure abstract class" one that contains nothing but
an interface of pure virtuals? If so, "pure abstract" sounds more like an OO term than a C++ term.

It is. And of course C++ is an OO language, so there's nothing wrong with
OO terminology.

[Merlin]

It is quite amazing how people can make assumptions and believe that
it is true. I am afraid you were wrong. Also the origin of the post is
not news.maxwell.sy r.edu as I live in the UK. But if it makes you
happy you can make further assumptions and feel that you are right.

The motivation behind those questions (yes there was more than one)
came from reading the GOF book. I wanted to understand the difference
between Interface and class inheritance. If you look on pages 16-18
you will see that abstract classes (pure or otherwise) mentioned. A
pure interface inheritance is said to be approximated in C++ by
inheriting publicly from a pure abstract class. So I wanted to know
what a pure abstract class was in c++.

You can be proud of your achievement of polluting this thread of
discussion.

Well done!

[Jeff Schwab]

Merlin wrote:

It is quite amazing how people can make assumptions and believe that
it is true. I am afraid you were wrong. Also the origin of the post is
not news.maxwell.sy r.edu as I live in the UK. But if it makes you
happy you can make further assumptions and feel that you are right.

The motivation behind those questions (yes there was more than one)
came from reading the GOF book. I wanted to understand the difference
between Interface and class inheritance. If you look on pages 16-18
you will see that abstract classes (pure or otherwise) mentioned. A
pure interface inheritance is said to be approximated in C++ by
inheriting publicly from a pure abstract class. So I wanted to know
what a pure abstract class was in c++.

You can be proud of your achievement of polluting this thread of
discussion.

Well done!

This seems to be a direct response to my brief message, although it does
not appear here... Is all of this vitriol actually directed at me?

[Jorge Rivera]

Who but an instructor or test writer would
write questions like that? Seriously, do you think that anyone would ever
actually have come up with those questions out of curiosity? Also, the post
comes via news.maxwell.sy r.edu, which sure looks like a school site to me.

Yes,

but finals were over two weeks ago at Syracuse...

If they are designing a test, it would be nice to have the input from
"experts".

If it's a student trying to learn (not to cheat), what's the harm?

If you feel this is inappropriate, you don't need to answer.

Let others post whatever they want. It's their problem...

JLR

[Howard]

"Jeff Schwab" <je******@comca st.net> wrote in message
news:xf******** ************@co mcast.com...

Merlin wrote:

It is quite amazing how people can make assumptions and believe that
it is true. I am afraid you were wrong. Also the origin of the post is
not news.maxwell.sy r.edu as I live in the UK. But if it makes you
happy you can make further assumptions and feel that you are right.

The motivation behind those questions (yes there was more than one)
came from reading the GOF book. I wanted to understand the difference
between Interface and class inheritance. If you look on pages 16-18
you will see that abstract classes (pure or otherwise) mentioned. A
pure interface inheritance is said to be approximated in C++ by
inheriting publicly from a pure abstract class. So I wanted to know
what a pure abstract class was in c++.

You can be proud of your achievement of polluting this thread of
discussion.

Well done!

This seems to be a direct response to my brief message, although it does
not appear here... Is all of this vitriol actually directed at me?

Nah, some of it was obviously directed at me (and Victor). I saw that .edu
address in the chain, which may or may not mean anything at all (a sender
usually has no control where it goes, especially when posted from
groups.google.c om). I still say the questions sounded very much like
homework. It wouldn't have seemed so if Merlin had simply asked "what is a
pure abstract class in C++", to which he would have gotten the reply "there
is no such thing in C++...maybe you mean an abstract class with no members?"

(By the way Merlin, what makes you assume we know what the heck the "GOF
book" is, let alone have a copy of it?)

*Assuming* you're telling truth Merlin, then I apologize for the previously
incorrect assumptions.

-Howard