C++ named requirements: MoveAssignable (since C++11)
Min standard notice:
Specifies that an instance of the type can be assigned from an rvalue argument.
# Notes
The type does not have to implement move assignment operator in order to satisfy this type requirement: a copy assignment operator that takes its parameter by value or as a const Type&, will bind to rvalue argument.
If a MoveAssignable class implements a move assignment operator, it may also implement move semantics to take advantage of the fact that the value of rv after assignment is unspecified.