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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - A tricky code sample"
href="https://bugs.llvm.org/show_bug.cgi?id=37852">37852</a>
</td>
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<tr>
<th>Summary</th>
<td>A tricky code sample
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</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>enhancement
</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>zhonghao@pku.org.cn
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The code is as follow:
#define _GLIBCXX_DEBUG
#include <vector>
struct T { int i; };
int swap_calls;
namespace std
{
template<>
void
vector<T, allocator<T> >::swap(vector<T, allocator<T> >&)
{ ++swap_calls; }
}
// Should use vector specialization for swap.
int main()
{
std::vector<T> A;
std::vector<T> B;
swap_calls = 0;
std::swap(A, B);
return swap_calls;
}
It comes from a gcc bug report:
<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=16021">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=16021</a>
The programmers of gcc have a long discussion on whether the above code is
legal.
I tried the latest g++, and it accepts the above code, but clang++ rejects it.
The error message is as follow:
code0.c.cpp:12:28: error: 'swap' is missing exception specification
'noexcept(noexcept(declval<std::__debug::vector<T, std::allocator<T> >::_Base
&>().swap(__x)))'
vector<T, allocator<T> >::swap(vector<T, allocator<T> >&)
^
noexcept(noexcept(declval<std::__debug::vector<T, std::allocator<T> >::_Base
&>().swap(__x)))
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/8.0.1/../../../../include/c++/8.0.1/debug/vector:688:7:
note: previous declaration is here
swap(vector& __x)
^
1 error generated.
You may have interests in reading the gcc bug report, and I am curious how you
consider the code sample. Is it buggy or not?</pre>
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