Re: pure virtual template...

From:

mathieu <mathieu.malaterre@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 27 Oct 2007 19:47:25 -0000

Message-ID:

<1193514445.455299.80010@19g2000hsx.googlegroups.com>

On 26 oct, 23:40, dvi...@gmail.com wrote:

On Oct 26, 2:49 pm, mathieu <mathieu.malate...@gmail.com> wrote:

On Oct 26, 2:19 pm, mathieu <mathieu.malate...@gmail.com> wrote:

Hi there,

I don't think I'll be able to describe my issue correctly, so
instead I'll just give a pseudo C++ code I am struggling with.
Basically I am looking for a 'pure virtual template' function that I
would be able to declare in the base class (*).

Hum...without much satisfaction here is my temporary solution.
Hopefully you guys will suggest something not involving making the
base class be polymorphic...

Not sure exactly what you are trying to achieve, but this works well
with template classes instead of template functions.
It does use polymorphism, but that is just another way of defining an
interface:

#include <iostream>

template <typename T>
struct Base
{
        virtual void foo(T x) = 0;

};

template <typename T>
struct A: Base<T>
{
        void foo(T x) { std::cout << "A=" << x << "\n"; }

};

template <typename T>
struct B: Base<T>
{
        void foo(T x) { std::cout << "B=" << x << "\n"; }

};

int main(int argc)
{
        Base<int> *base;
        if (argc > 1)
                base = new A<int>;
        else
                base = new B<int>;
        base->foo(45);
        return 0;

}

I can't move the template at the class level unfortunately.

Explanation:
My objects can be serialized either in big endian or little endian. So
the design is :

struct Object
{
  ...
  void Read<Swapper>(ostream &os) { ... }
  void Write<Swapper>(ostream &os) { ... }
}

Where swapper is either a no-op or actually do a byte-swap. So
template at the class level would not make much sense.

Thanks anyway,
-Mathieu