C++11: Inheriting Base Class Constructors

Sometimes a derived class’s constructors simply mimic the base class’s constructors. A frequently requested convenience feature for C++11 was the ability to inherit a base class’s constructors. You can now do this by explicitly including a using declaration of the form

anywhere in the derived-class definition. In the preceding declaration, BaseClass is the base class’s name. With a few exceptions (listed below), for each constructor in the base class, the compiler generates a derived-class constructor that calls the corresponding base-class constructor. The generated constructors perform only default initialization for the derived class’s additional data members. When you inherit constructors:

• By default, each inherited constructor has the same access level (public, protected or private) as its corresponding base-class constructor.

• The default, copy and move constructors are not inherited.

• If a constructor is deleted in the base class by placing = delete in its prototype, the corresponding constructor in the derived class is also deleted.

• If the derived class does not explicitly define constructors, the compiler generates a default constructor in the derived class—even if it inherits other constructors from its base class.

• If a constructor that you explicitly define in a derived class has the same parameter list as a base-class constructor, then the base-class constructor is not inherited.

• A base-class constructor’s default arguments are not inherited. Instead, the compiler generates overloaded constructors in the derived class. For example, if the base class declares the constructor

the compiler generates the following two derived-class constructors without default arguments

These each call the BaseClass constructor that specifies the default arguments.