Why is a vector considered nothrow_move_constructible?

Question

Vector move constructor specification (copied outside the standard):

vector(vector&&); 

Note the lack of noexcept . But both gcc 4.8 and Clang 3.2 report that std::is_nothrow_move_constructible<std::vector<int>>::value returns true (ie, 1):

 #include<vector> #include<iostream> int main() { std::cout << std::is_nothrow_move_constructible<std::vector<int>>::value << '\n'; } 

What is the reason for this apparent discrepancy?

Answer 1

The standard allows the implementation to strengthen the specification of a method exception according to

17.6.5.12 Limitations on Exception Handling [res.on.exception.handling]

⁴ Destructor operations defined in the C ++ standard library should not throw exceptions. Each destructor in the C ++ standard library should behave as if it had an exception specification to exclude metadata. Any other functions defined in the C ++ standard library that do not have an exception specification may raise exceptions defined during implementation, unless otherwise specified. ¹⁹¹ An implementation can enhance this implicit exception specification by adding an explicit one. ¹⁹²