NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/gnu/g/help/1593

Text File | 1992-12-15 | 1.9 KB | 55 lines

Xref: sparky gnu.g++.help:1593 comp.lang.c++:17995
Newsgroups: uw.dcs.general,gnu.g++.help,comp.lang.c++
Path: sparky!uunet!stanford.edu!agate!doc.ic.ac.uk!warwick!dcs.warwick.ac.uk!maths.warwick.ac.uk!steve
From: [e-mail] (Steve Rumsby)
Subject: Re: Deriving C++ Templates
Message-ID: <[e-mail]>
Sender: [e-mail] (Network News)
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Organization: Geometry Group, Maths Institute, Warwick University, UK.
References:  <[e-mail]>
Date: Tue, 15 Dec 1992 16:20:41 GMT
Lines: 41

In article <[e-mail]>, [e-mail] (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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