<html>
<head>
<base href="https://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Call to friend function template of a class template considered ambiguous"
href="https://llvm.org/bugs/show_bug.cgi?id=31507">31507</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Call to friend function template of a class template considered ambiguous
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>t@sharklasers.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The following code attempts to declare a function template as a friend to a
class template and defines it subsequently:
template <typename T>
class A {
template <typename T1, typename T2>
friend auto func(T1 a, T2 b);
private:
T a;
};
template <typename T1, typename T2>
auto func(T1 x, T2 y) {
return x.a + y.a;
}
int main() {
A<int> a;
A<double> b;
func(a, b);
}
Clang version 4.0.0 (trunk 290784) rejects this code saying:
test.cpp:21:5: error: call to 'func' is ambiguous
func(a, b);
^~~~
test.cpp:6:17: note: candidate function [with T1 = A<int>, T2 = A<double>]
friend auto func(T1 a, T2 b);
^
test.cpp:13:6: note: candidate function [with T1 = A<int>, T2 = A<double>]
auto func(T1 x, T2 y) {
GCC, ICC and MSVC accept that code. With the following change:
template <typename T>
class A {
template <typename T1, typename T2>
friend auto func(T1 x, T2 y) {
return x.a + y.a;
}
private:
T a;
};
int main() {
A<int> a;
A<double> b;
func(a, b);
}
Clang accepts, however GCC, ICC and MSVC reject with similar error messages:
test.cpp: In instantiation of ‘class A<double>’:
test.cpp:16:15: required from here
test.cpp:6:17: error: redefinition of ‘template<class T1, class T2> auto
func(T1, T2)’
friend auto func(T1 x, T2 y) {
^~~~
test.cpp:6:17: note: ‘template<class T1, class T2> auto func(T1, T2)’
previously defined here
test.cpp: In instantiation of ‘auto func(T1, T2) [with T1 = A<int>; T2 =
A<double>; T = int]’:</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>