Mid-Level

Returning a moved big object will actually create extra overhead for the compiler, as a zero-cost operation is traded for a cheap move operation.

Ideally, we should never throw on the move Constructor of an object. If a move constructor throws an exception while a vector is resizing, the vector is in a “broken” state: half of the elements are in the new memory, and half are in the old memory. Move operations often modify the source object (leaving it empty or null), making it dangerous to undo the changes. Therefore, the compiler wants to avoid this risk and uses a copy rather than a movment. We want to avoid this, and the way to do this is to declare the move constructor as noexcept. Like this, we give the promise that we do not throw, and the compiler can safely use it. ...

Converting a base-class pointer to a derived-class pointer is downcasting. We should be careful when we do that in order to avoid UBs.