TITLE: templates 101

(Newsgroups: comp.lang.c++, 22 Sep 97)


KOH: Shannon Koh <shack19@cybertech.com.sg>

> Has anyone ever wondered about the inheritance of template classes?


BJARNE: bs@research.att.com (Bjarne Stroustrup)

Yes, someone has :-)


KOH:

> Can a template class inherited from a normal class?


BJARNE: 

Yes:
	class B { ... };

	template<class T> class X : public B { ... };


KOH:

> Or can a normal class inherit from a template class?


BJARNE: 

No, if you mean this:

	class D1 : public X { ... };	// error X is a template (not a class)

Yes, if you mean this:

	class D2 : public X<int> { ... };	// X<int> is a class


KOH:

>How about one template class inheriting from another template class,


BJARNE: 

Yes:

	template<class T> class X2 : public X<T> { ... };


KOH:

> and better still, with different template classes?


BJARNE: 

Yes, if you mean something like this:

	template<class T> class Z { ... };

	template<class T> class X3 : public X<T>, public Z<T> { ... };

You can even have a template class inherit from one of its template
parameters:

	template<class T> class X4 : public T { ... };


KOH:

> Seeking all who know and have experienced... Bye!


BJARNE: 

Hmm. That's quite a lot of people.

Actually, the real question is not just what you can do, by why you would
want to do it. That is, what are good uses of the constructs presented above?

For some answers to many such questions, see

	Stroustrup: The C++ Programming Language (3rd Edition)

and also

	Stroustrup: The Design and Evolution of C++

There are information about these books on my homepages.

	- Bjarne

Bjarne Stroustrup, AT&T Labs, http://www.research.att.com/~bs