Re: template and typedef

From:

Kira Yamato <kirakun@earthlink.net>

Newsgroups:

comp.lang.c++

Date:

Thu, 21 Feb 2008 11:07:45 -0500

Message-ID:

<2008022111074575249-kirakun@earthlinknet>

On 2008-02-21 10:59:16 -0500, Kira Yamato <kirakun@earthlink.net> said:

On 2008-02-21 05:05:38 -0500, Berardino la Torre
<berardino.latorre@hotmail.com> said:

Hi All,

is it possible to do something like this ? :

template <typename Base>
class Object : public Base::Interface {
};

g++ seems to complain that you cannot inherit from an incomplete type Base.

This is interesting. Just when you think you've figured out how
template works, here comes another example showing you how much you
don't know.

Well I suppose it makes sense that this should be an error. It's
basically a circular definition that could lead to infinite regress.
For example,

template<class T>
class A : public T {};

class B : public A<B>
{
int x;
};

But this code expands to

class B : public B
{
int x;
};

Hence the infinite regress.

class IA{
  virtual void print()=0;
};

class A : public Object<A>{
public:
  typedef IA A::Interface;
  void print(){
  }
};

Seems like your goal is to have class A inherit from A::Interface. So,
why not consider the following:

class IA {};

class A : public IA
{
public:
typedef IA Interface;
};

int main(){

return 0;
}

--

// kira