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Date: Thu, 27 May 2004 11:47:00 -0000
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From: "bangerth at dealii dot org" <gcc-bugzilla@gcc.gnu.org>
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Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug c++/15664] Linker fails to find (inline) function
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X-SW-Source: 2004-05/txt/msg03111.txt.bz2
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------- Additional Comments From bangerth at dealii dot org  2004-05-26 19:21 -------
Your code looks like this: 
------------------- 
template<typename E, template<typename>class A1, template<typename>class A2> 
bool operator==(const Powerbase<E, A1>& p1, const Powerbase<E, A2>& p2); 
 
template<typename E, template<typename> class Alloc> 
class Powerbase 
{ 
    template<template<typename>class A2> 
    friend 
    bool operator==(const Powerbase<E, Alloc>& p1, 
                    const Powerbase<E, A2>& p2); 
}; 
 
template<typename E, template<typename> class A1, template<typename>class A2> 
inline 
bool operator==(const Powerbase<E, A1>& p1, 
                const Powerbase<E, A2>& p2) { 
  return p1.Relop(p2, Powerbase<E, A1>::equalOp); 
} 
------------------------- 
The problem with it is that the friend declaration is not for the function 
you have previously declared (easily seen by the fact that it has only one 
instead of three template arguments). Thus, the compiler assumes that it 
is a previously undeclared overload of operator== and injects it into the 
global namespace. You therefore have two overloaded declarations, and the 
compiler later on in the program happens to pick the one that was 
declared in the friend declaration. It doesn't exist, though, thus the 
linker error. 
 
The general rule is: since there are no partial specializations for template 
functions, the only thing you can declare a friend is a general template, 
in this case the three-argument template. You can't declare only certain 
possible instantiations of a template a friend. 
 
W. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15664