Tightening the conditions for generating implicit moves

Change in 12.8 class.copy paragraph 8:

If the class definition does not explicitly declare a copy constructor, and there is no user-declared move constructor, and there is no user-declared move assignment operator, a copy constructor is implicitly declared as defaulted (8.4 dcl.fct.def 8.4.2 dcl.fct.def.default). Such implicit declaration is deprecated if the class has a user-declared copy assignment operator or a user-declared destructor. ...

If the class definition of a class X does not explicitly declare a move constructor, one will be implicitly declared as defaulted if and only if

• X does not have a user-declared copy constructor, and
• X does not have a user-declared copy assignment operator,
• X does not have a user-declared move assignment operator,
• X does not have a user-declared destructor, and
• the move constructor would not be implicitly defined as deleted.

If the class definition does not explicitly declare a copy assignment operator, there is no user-declared move constructor, and there is no user-declared move assignment operator, a copy assignment operator is implicitly declared as defaulted (8.4 dcl.fct.def 8.4.2 dcl.fct.def). Such implicit declaration is deprecated if the class has a user-declared copy constructor or a user-declared destructor. ...

If the class definition of a class X does not explicitly declare a move assignment operator, one will be implicitly declared as defaulted if and only if

• X does not have a user-declared copy constructor,
• X does not have a user-declared move constructor,
• the X does not have a user-declared copy assignment operator is not user-declared and,
• X does not have a user-declared destructor, and
• the move assignment operator would not be implicitly defined as deleted.

[ Example: ... ]

The implicit declaration of a copy constructor is deprecated if the class has a user-declared copy assignment operator or a user-declared destructor. The implicit declaration of a copy assignment operator is deprecated if the class has a user-declared copy constructor or a user-declared destructor. (12.4 class.dtor, 12.8 class.copy)