For value-like types, consider providing a `noexcept` swap function

Reason

A swap can be handy for implementing a number of idioms, from smoothly moving objects around to implementing assignment easily to providing a guaranteed commit function that enables strongly error-safe calling code. Consider using swap to implement copy assignment in terms of copy construction. See also destructors, deallocation, and swap must never fail.

Example, good

class Foo {
public:
    void swap(Foo& rhs) noexcept
    {
        m1.swap(rhs.m1);
        std::swap(m2, rhs.m2);
    }
private:
    Bar m1;
    int m2;
};

Providing a non-member swap function in the same namespace as your type for callers' convenience.

void swap(Foo& a, Foo& b)
{
    a.swap(b);
}

Enforcement

• Non-trivially copyable types should provide a member swap or a free swap overload.
• (Simple) When a class has a swap member function, it should be declared noexcept.