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From: jhrwalter@yahoo.com (Joerg Walter)
Newsgroups: comp.std.c++
Subject: Problem with function template overload resolution
Date: Sat, 20 Sep 2003 16:49:05 +0000 (UTC)
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Xref: archiver1.google.com comp.std.c++:20826

Hello,

I've already tried to discuss the following two programs on
comp.lang.c++.moderated. Kresimir Fresl's test case

----------
#include <iostream>

template<typename A, typename T>
struct result {};

template<typename T>
struct arg1 {
   typedef T value_type;
};
template<typename T>
struct arg2 {
   typedef T value_type;
};

template<typename A>
result<A, typename A::value_type> foo(A const& a) {
   std::cout << "foo<A>" << std::endl;
   return result<A, typename A::value_type>();
}
template<typename R, typename A>
R foo(A const& a) {
   std::cout << "foo<R, A>" << std::endl;
   return R();
}

int main() {
   arg1<int> s1;
   arg2<int> s2;

   foo(s2);    // OK

   foo<arg1<int>, arg2<int> >(s2);  // OK
   foo<arg2<int>, arg2<int> >(s2);  // OK

   foo<arg1<int> >(s2);    // OK
   foo<arg2<int> >(s2);    // Ambigous?
}

----------

is accepted by GCC 3.3.1, a program run results in

foo<A>
foo<R, A>
foo<R, A>
foo<R, A>
foo<R, A>

ICC 7.1 and MSVC 7.1 reject this code. Patrick Kowalzick's reduced
test case

----------
#include <iostream>

// no basic types to avoid automatic casting
class arg_1 {};
class arg_2 {};

template<typename A> void foo(A const& a)
{
   std::cout << "foo<A>" << std::endl;
}

template<typename R, typename A> void foo(A const& a)
{
   std::cout << "foo<R, A>" << std::endl;
}

int main() {

 foo ( arg_1() );

 foo < arg_1 > ( arg_1() );  // Ambigous?
 foo < arg_2 > ( arg_1() );  // OK

 foo< arg_1 , arg_1 > ( arg_1() );  // OK
 // foo< arg_1 , arg_2 > ( arg_1() );  // no casting from 1 to 2
 foo< arg_2 , arg_1 > ( arg_1() );  // OK
 // foo< arg_2 , arg_2 > ( arg_1() );  // no casting from 1 to 2

}

----------

is accepted by GCC 3.3.1 and ICC 7.1. MSVC 7.1 rejects that code.

Are these legal C++ programs?

Thanks for any enlightenment,
Joerg Walter

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