Make move operations `noexcept`

Reason

A throwing move violates most people's reasonable assumptions. A non-throwing move will be used more efficiently by standard-library and language facilities.

Example

template<typename T>
class Vector {
public:
    Vector(Vector&& a) noexcept :elem{a.elem}, sz{a.sz} { a.elem = nullptr; a.sz = 0; }
    Vector& operator=(Vector&& a) noexcept {
        if (&a != this) {
            delete elem;
            elem = a.elem; a.elem = nullptr;
            sz   = a.sz;   a.sz   = 0;
        }
        return *this;
    }
    // ...
private:
    T* elem;
    int sz;
};

These operations do not throw.

Example, bad

template<typename T>
class Vector2 {
public:
    Vector2(Vector2&& a) noexcept { *this = a; }             // just use the copy
    Vector2& operator=(Vector2&& a) noexcept { *this = a; }  // just use the copy
    // ...
private:
    T* elem;
    int sz;
};

This Vector2 is not just inefficient, but since a vector copy requires allocation, it can throw.

Enforcement

(Simple) A move operation should be marked noexcept.