🚀 go-pugleaf

In article <1992Dec15.160544.26065@dcs.warwick.ac.uk>, jas@dcs.warwick.ac.uk (Jason Morris) writes:
> 
>   I have a C++ class, Matrix, and from this I derived a class, Vector, which
> is simply a 1-D Matrix. The problem was that I could only have a Matrix of,
> say floats, but I wanted something more flexible that could hold anything. So
> I changed Matrix to be a template with the type of element given as the
> template arguement. That works fine.
>   However, I am now having problems in deriving Vector. Is it actually
> possible to use a template as a base class? Or are parameterised types and
> inheritance mechanisms mutually exlusive? 
>
Remember that a class template defines a family of classes, and is not a
class itself. It is therefore not possible to use the template as a base class
(since it is not a class) but it is possible to use members of the defined
family as base classes. So, given:

	template <class T>
	class foo {
		// junk...
	};

You can say:

	class foobar : private foo<int> {
		// junk...
	};

You can also say:

	template <class T>
	class foobaz : private foo<T> {
		// junk...
	};

I think this final example does what you want - you derive Vector<T> from
Matrix<T>.

Steve.
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In article <1992Dec15.160544.26065@dcs.warwick.ac.uk> jas@dcs.warwick.ac.uk (Jason Morris) writes:
>
>  However, I am now having problems in deriving Vector. Is it actually
>possible to use a template as a base class? Or are parameterised types and
>inheritance mechanisms mutually exlusive? 
>
	It is definitely the intent this be allowed, BC allows it.
So do most of the more recent versions of other compilers. Some older
compilers may have had problems.


-- 
;----------------------------------------------------------------------
        JOHN (MAX) SKALLER,         maxtal@extro.ucc.su.oz.au
	Maxtal Pty Ltd, 6 MacKay St ASHFIELD, NSW 2131, AUSTRALIA
;--------------- SCIENTIFIC AND ENGINEERING SOFTWARE ------------------

You'll have to explicitly state in the derived class which type of the
base class you want to use, ie:

   template <class C>
      class Base<T> { };

   template <class C>
      class Derived<C> : Base <C> { };

or similar, or simpler, like fewer template dependencies.

By the way, for good programming practice, consider deriving Matrix from
Vector rather than the other way round...


Maz