template and inheritanc

[Tony Johansson]

Hello Experts

To derive a concrete class from a template class in invalid. Why??
So you should not be able have something like this
class Derived : public Base<int, 100>

It's valid to derive a template class from a base class that is also a
template class.
It's valid to derive a template class from a concrete base class.

I do know inheritance but I have never used it together with template
classes.
How should inheritance be understood when we have to do with templated
classes
Can you explain something about that.

Many thanks

//Tony

[Bob Hairgrove]

On Mon, 15 Aug 2005 23:55:16 GMT, "Tony Johansson"
<jo*****************@telia.com> wrote:

Hello Experts

To derive a concrete class from a template class in invalid. Why??
So you should not be able have something like this
class Derived : public Base<int, 100>

It's valid to derive a template class from a base class that is also a
template class.
It's valid to derive a template class from a concrete base class.

I do know inheritance but I have never used it together with template
classes.
How should inheritance be understood when we have to do with templated
classes
Can you explain something about that.

Many thanks

//Tony

I strongly recommend that you read the following book:
"C++ Templates -- The Complete Guide"
by David Vandevoorde and Nicolai M. Josuttis
Addison-Wesley (ISBN 0-201-73484-2)

After you've read it, please drop in again.

--
Bob Hairgrove
No**********@Home.com

[Victor Bazarov]

Tony Johansson wrote:

To derive a concrete class from a template class in invalid.
There is no such thing as a "template class". There is a "class"
and a "class template". I presume you mean the latter.
Why??
Because such are the rules of the language. The base class becomes
a sub-object in th ederived class object. If the base class is
a template, there is no way to create a sub-object, is there? We
can only create objects from a concrete types.
So you should not be able have something like this
class Derived : public Base<int, 100>
Huh???

That's not deriving from a template. That's deriving from a class,
an instantiation of the template. It should work just fine, assuming
that 'Base' is declared, for example, like

template<class T, int a> class Base;
It's valid to derive a template class from a base class that is also a
template class.
(still presuming you mean "class template")... Yes.
It's valid to derive a template class from a concrete base class.
Yes. You can define a class template and give it a base class.
I do know inheritance but I have never used it together with template
classes.
Nothing special. The concepts are orthogonal.
How should inheritance be understood when we have to do with templated
classes
....with class templates... What's different? If you specify some
particular template arguments, the template becomes a concrete type.
Now combine the two concepts.
Can you explain something about that.

What book are you reading that doesn't explain it?

Please do not ask us to write another book for you in a newsgroup
post. Ask specific questions.

V