https://bugs.llvm.org/show_bug.cgi?id=39619
Bug ID: 39619
Summary: iterator_traits isn't SFINAE-friendly enough
Product: libc++
Version: 7.0
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: All Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: enieb...@boost.org
CC: llvm-bugs@lists.llvm.org, mclow.li...@gmail.com
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.
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