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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 - iterator_traits isn't SFINAE-friendly enough"
href="https://bugs.llvm.org/show_bug.cgi?id=39619">39619</a>
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<th>Summary</th>
<td>iterator_traits isn't SFINAE-friendly enough
</td>
</tr>
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<th>Product</th>
<td>libc++
</td>
</tr>
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<th>Version</th>
<td>7.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>All Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>eniebler@boost.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
</td>
</tr></table>
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<div>
<pre>The following program fails to compile:
#include <iterator>
struct not_an_iterator {
using iterator_category = std::input_iterator_tag;
};
std::iterator_traits<not_an_iterator> x;
The error is as follows:
In file included from <source>:1:
/opt/compiler-explorer/clang-trunk-20181110/bin/../include/c++/v1/iterator:456:29:
error: no type named 'difference_type' in 'not_an_iterator'
typedef typename _Iter::difference_type difference_type;
~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
/opt/compiler-explorer/clang-trunk-20181110/bin/../include/c++/v1/iterator:467:8:
note: in instantiation of template class
'std::__1::__iterator_traits_impl<not_an_iterator, true>' requested here
: __iterator_traits_impl
^
/opt/compiler-explorer/clang-trunk-20181110/bin/../include/c++/v1/iterator:482:7:
note: in instantiation of template class
'std::__1::__iterator_traits<not_an_iterator, true>' requested here
: __iterator_traits<_Iter, __has_iterator_category<_Iter>::value> {};
^
<source>:5:39: note: in instantiation of template class
'std::__1::iterator_traits<not_an_iterator>' requested here
std::iterator_traits<not_an_iterator> x;
^
In file included from <source>:1:
/opt/compiler-explorer/clang-trunk-20181110/bin/../include/c++/v1/iterator:457:29:
error: no type named 'value_type' in 'not_an_iterator'
typedef typename _Iter::value_type value_type;
~~~~~~~~~~~~~~~~^~~~~~~~~~
/opt/compiler-explorer/clang-trunk-20181110/bin/../include/c++/v1/iterator:458:29:
error: no type named 'pointer' in 'not_an_iterator'
typedef typename _Iter::pointer pointer;
~~~~~~~~~~~~~~~~^~~~~~~
/opt/compiler-explorer/clang-trunk-20181110/bin/../include/c++/v1/iterator:459:29:
error: no type named 'reference' in 'not_an_iterator'
typedef typename _Iter::reference reference;
~~~~~~~~~~~~~~~~^~~~~~~~~
4 errors generated.
The primary iterator_traits template merely tests for the presence of a nested
::iterator_concept typedef. It is required by the standard to test for the
presence of all the iterator typedefs: ::value_type, ::difference_type,
::reference, and ::pointer.</pre>
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