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From: =?ISO-8859-1?Q?Falk_Tannh=E4user?= <falk.tannhauser@crf.canon.fr>
Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng
Subject: Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: Wed, 09 Mar 2005 18:31:52 +0100
Organization: Canon Research Centre France
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Xref: g2news1.google.com comp.lang.ada:8954 comp.lang.c++:44817
 comp.realtime:1144 comp.software-eng:4702
Date: 2005-03-09T18:31:52+01:00
List-Id: <comp.lang.ada>

Pascal Obry wrote:
> Hum, since you answered "no" and I answered "yes" it seems there is something
> about "templates recurse" that I did not understand. In short what is a
> recursive template in C++ ?

One example in C++:

   template<unsigned N> struct factorial
   {
     static unsigned const value = N * factorial<N-1>::value;
   };

   // Partial template specialisation to terminate the recursion:
   template<> struct factorial<0>
   {
     static unsigned const value = 1;
   };

With this, 'factorial<7>::value' will be a compile time constant equal to 5040.

Another example:

   template<typename T> struct pointer_info
   {
     typedef T base_type;
     static unsigned const indir_level = 0;
   };

   // Partial template specialisation for types that are pointers:
   template<typename T> struct pointer_info<T*>
   {
     typedef typename pointer_info<T>::base_type base_type;
     static unsigned const indir_level = pointer_info<T>::indir_level + 1;
   };

With this, suppose that you have
   typedef int***** foo_t;
Then 'pointer_info<foo_t>::base_type' is a typedef (alias) for 'int' and
'pointer_info<foo_t>::indir_level' is a compile time constant equal to 5.

Falk