Re: Can this be done with templates?

From:

kwikius <andy@servocomm.freeserve.co.uk>

Newsgroups:

comp.lang.c++

Date:

Sat, 1 Mar 2008 05:20:39 -0800 (PST)

Message-ID:

<92e9e2af-afbb-48ba-9f44-7c04624ee594@q33g2000hsh.googlegroups.com>

On Mar 1, 10:43 am, sip.addr...@gmail.com wrote:

On Mar 1, 4:09 am, Ian Collins <ian-n...@hotmail.com> wrote:

sip.addr...@gmail.com wrote:

OK, that makes a little more sense.

If the derived class don't add any functionality, why have them? I=

f you

want a family of unique classes, how about

template <unsigned N>
class D : public B
{
public:
D(const std::string& id) : B(id) {}

};

template <unsigned N0, unsigned N1>
class DD : public D<N0>
{
public:
D(const std::string& id) : D<N0>(id) {}

};

then you can instantiate D<1>, D<2>, DD<1,1> etc.

Thanks, but I was looking for something more generic. For instance,
this inheritance tree could be deeper (imagine having like 20 classes,=

and a tree depth of 5 for instance). Also, I named the classes like
D1, D11, etc. but it was just for brevity. In a normal situation, I'd
use a proper name in each case. This is why I'd like some generator
that also names the classes I want to instantiate, and also defines
its hierarchy.

Would it be possible to achieve this?

I still can't see why you'd want a tree of derived classes that don't
add functionality to their base.

If you want to be lazy with typing, resort to a macro!

I thought it would be possible to rely on the compiler, for better
type safety.

The rationale of this is just proof of concept, so there's no specific
practical application to it at the moment.-

I don't know whether the following is what you mean:

#include <string>

template <typename Base, int Tag = 0>
struct D : Base{
  D(std::string const & id) : Base(id){}
};

struct B{
  B(const std::string& id) : id_(id) {}
  std::string id_;
};

#include <iostream>
int main()
{
  typedef D<B> D1;
  typedef D<B,1> D2;
  typedef D<D1> D11;
  D11 d11("hello") ;
  std::cout << d11.id_ <<'\n';
}

regards
Andy Little