[llvm-bugs] [Bug 32605] New: common_type<T> is not SFINAE-friendly

via llvm-bugs llvm-bugs at lists.llvm.org
Mon Apr 10 12:45:24 PDT 2017


            Bug ID: 32605
           Summary: common_type<T> is not SFINAE-friendly
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: rs2740 at gmail.com
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

The current implementation

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS common_type<_Tp>
    typedef typename common_type<_Tp, _Tp>::type type;

is incorrect, because common_type<_Tp, _Tp>::type need not exist, in which case
the current implementation will cause a hard error. This is the case for
abominable function types (although they currently fail due to a separate bug
in std::decay), and user-defined specializations may also fail to supply a
::type member. P0548 requires this case to be SFINAE-friendly.

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