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Date: Tue, 16 Apr 2002 10:16:00 -0000
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Subject: c++/6327: g++ problems where partial specializing nested templates
X-SW-Source: 2002-04/txt/msg00844.txt.bz2
List-Id: <gcc-prs.sourceware.org>


>Number:         6327
>Category:       c++
>Synopsis:       g++ problems where partial specializing nested templates
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Apr 16 10:16:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     g++
>Release:        Thread model: single - gcc version 3.0
>Organization:
>Environment:
Mandrake 8.0 on AMD Athlon 800
>Description:
It seems that the compiler doesn't use correctly partial specialization of a nested template, even if it produce correct code when template are not nested.
>How-To-Repeat:
#include <typeinfo>
#include <iostream>

// generic template
template<class T>
struct Array_traits
{
  template<class U>
  struct Rebind
  {
    typedef U Type;
  };
};

// partial specialization for arrays
template<class T, int N>
struct Array_traits<T[N]>
{
  template<class U>
  struct Rebind
  {
    typedef Array_traits<T>::Rebind<U>::Type Type[N];
  };
};

int main()
{
  typedef int array_of_int[10][20][30];
  Array_traits<array_of_int>::Rebind<float>::Type array_of_float;

  // it prints out A10_A20_A30_i
  std::cout << typeid(array_of_int).name() << std::endl;

  // it should print A10_A20_A30_f, but it prints A10_f
  std::cout << typeid(array_of_float).name() << std::endl;
}
>Fix:
Here is a work-around that doesn't use nested templates:

// generic template
template<class T, class U> 
struct Array_rebind
{
  typedef U Type;
};

// partial specialization
template<class T, int N, class U>
struct Array_rebind<T[N], U>
{
  typedef Array_rebind<T,U>::Type Type[N];
};
>Release-Note:
>Audit-Trail:
>Unformatted: