Object-Oriented Programming-c++_ lesson 22 upward styling

An assignment compatibility rule is a case in which an object of a derived class can be used as an object of the base class in a public-derived case.

The contract class derived is derived from the class base public, which refers to the following 3 scenarios:

(1) A derived object can be assigned to an object of the base class. For example:

Derived D;

Base b;

B=d;

(2) An object of a derived class can initialize a reference to a base class. For example:

Derived D;

base& Br=d;

(3) The address of the object of the derived class can be assigned to a pointer to the base class. For example:

Derived D;

Base *pb=&d;

A pointer or reference to a parent class is an upward shape.

Parent class: People

Subclass: Student

Students can be seen as people, but they can't be seen as students

Object-Oriented Programming-c++_ lesson 22 upward styling