The Rule of Three

If your class directly manages some kind of resource (such as a new'ed pointer), then you almost certainly need to hand-write three special member functions:

• A destructor to free the resource
• A copy constructor to copy the resource
• A copy assignment operator to free the left-hand resource and copy the right-hand one
• Use the copy-and-swap idiom to implement assignment.

The Rule of Zero

If your class does not directly manage any resource, but merely uses library components such as vector and string, then you should strive to write no special member functions.

Default them all

• Let the compiler implicitly generate a default destructor
• Let the compiler implicitly generate the copy constructor
• Let the compiler implicitly generate the copy assignment operator
• (But your own swap might improve performance)