Re: Templates and inheritance

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 17 Oct 2008 00:38:11 -0700 (PDT)

Message-ID:

<b84a2fd4-16e6-4e1a-9255-5d08f86c5add@m36g2000hse.googlegroups.com>

On Oct 16, 4:35 pm, Isaac Gelado <igel...@gmail.com> wrote:

I am having problems with inheritance in templates classes.
Say I have the following classes:

class A {};
class B: public A {};
template<typename T> class C {};

Now in my code I have something like:

C<A *> *myAPtr;
myAPtr = new C<B *>();

I'm getting an error saying that conversion from C<B *> to C<A *> is
not possible.

Normal. C<B*> and C<A*> are two completely unrelated classes.

Does it mean I can no use subclassing with templates without
using ugly casts?

Sure you can, but you're not deriving anything in the templates
here. Derivation in template classes works exactly like
derivation for any other class, and given:

    class Toto
    {
        // ...
        A* pA ;
    } ;

    class Titi
    {
        // ...
        B* pB ;
    } ;

there's no implicit conversion (nor should there be) Titi* to
Toto*. If you replace Toto with C<A*> and Titi with C<B*>, why
would you expect anything different?

--
James Kanze (GABI Software) email:james.kanze@gmail.com
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