https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71771
Bug ID: 71771
Summary: DR 685 applied incorrectly
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: Casey at Carter dot net
Target Milestone: ---
The resolution of LWG DR 685
(http://cplusplus.github.io/LWG/lwg-defects.html#685) *replaces* the non-member
operator- of reverse_iterator and move_iterator with a cross-type overload
constrained via expression SFINAE on the return type.
libstdc++ trunk adds the cross-type overload for reverse_iterator, but *leaves
the old single-type overload in place*, so operator- does not properly SFINAE
for two reverse_iterators with the same (non-differentiable) base type.
move_iterator also has the new cross-type overload, its old single-type
overload has been left in place but constrained similarly. While technically
conforming, the result is that for a move_iterator i, "i - {}" and "{} - i"
will match this old single-type overload instead of being ill-formed.
