[Bug libstdc++/69301] New: std::atomic::load() won't compile if T doesn't have a default constructor

[anthony.ajw at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69301

            Bug ID: 69301
           Summary: std::atomic<T>::load() won't compile if T doesn't have
                    a default constructor
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anthony.ajw at gmail dot com
  Target Milestone: ---

Created attachment 37360
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37360&action=edit
atomic_no_default_constructor.cpp

The attached simple code fails to compile with g++ 5.3 in C++1y mode because
NoDefaultConstructor doesn't have a default constructor. The error message is
quoted below.


g++-5 -std=c++1y atomic_no_default_constructor.cpp 
In file included from atomic_no_default_constructor.cpp:1:0:
/usr/include/c++/5/atomic: In instantiation of ‘_Tp
std::atomic<_Tp>::load(std::memory_order) const [with _Tp =
NoDefaultConstructor; std::memory_order = std::memory_order]’:
atomic_no_default_constructor.cpp:11:12:   required from here
/usr/include/c++/5/atomic:234:13: error: no matching function for call to
‘NoDefaultConstructor::NoDefaultConstructor()’
         _Tp tmp;
             ^
atomic_no_default_constructor.cpp:5:15: note: candidate: constexpr
NoDefaultConstructor::NoDefaultConstructor(int)
     constexpr NoDefaultConstructor(int i_) noexcept : i(i_) {}
               ^
atomic_no_default_constructor.cpp:5:15: note:   candidate expects 1 argument, 0
provided
atomic_no_default_constructor.cpp:3:8: note: candidate: constexpr
NoDefaultConstructor::NoDefaultConstructor(const NoDefaultConstructor&)
 struct NoDefaultConstructor{
        ^
atomic_no_default_constructor.cpp:3:8: note:   candidate expects 1 argument, 0
provided
atomic_no_default_constructor.cpp:3:8: note: candidate: constexpr
NoDefaultConstructor::NoDefaultConstructor(NoDefaultConstructor&&)
atomic_no_default_constructor.cpp:3:8: note:   candidate expects 1 argument, 0
provided