Does Visual Studio 2017 need an explicit move constructor declaration?

Question

The below code can be compiled successfully using Visual Studio 2015, but it failed using Visual Studio 2017. Visual Studio 2017 reports:

error C2280:

Answer 1

Visual Studio 2017:

As @Evg indicated, the Visual Studio 2017's vector sourcecode finally call into _Uninitialized_copy because the implicitly-declared move constructor of Node is considered as not-nothrow (is_nothrow_move_constructible is false) and is_copy_constructible is true in Visual Studio 2017.

1) About is_nothrow_move_constructible:

https://en.cppreference.com/w/cpp/language/move_constructor says:

The implicitly-declared (or defaulted on its first declaration) move constructor has an exception specification as described in dynamic exception specification (until C++17)exception specification (since C++17)

Maybe it's reasonable to consider is_nothrow_move_constructible as false beacause Node's data member std::unordered_map's move constructor is not marked as noexcept.

2) About is_copy_constructible:

As @Oliv says, it's seemingly not logical to compute is_copy_constructible as true, specially considering the fact that Node is not copy_constructible has been detected and reported as compile error by Visual Studio 2017 compiler. Node is not copy_constructible beacause std::unique_ptr is not copy_constructible.

Visual Studio 2015:

Visual Studio 2015's vector has a different implemetation. vec.push_back->_Reserve->_Reallocate->_Umove->_Uninitialized_move_al_unchecked->_Uninitialized_move_al_unchecked1->std::move(node). is_nothrow_move_constructible and is_copy_constructible are not involved. It just call std::move(node) instead of copy constructor. So the sample code can be compiled successfully using Visual Studio 2015.