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This article mainly introduces "php richter replacement principle example analysis," in daily operation, I believe many people in php richter replacement principle example analysis problems exist doubts, small make up access to all kinds of information, sorting out simple and easy to use operation methods, hope to answer "php richter replacement principle example analysis" doubts helpful! Next, please follow the small series to learn together!

In PHP, the Richter substitution principle is a constraint on class inheritance. The main idea of the principle is that classes that are not suitable, have redundant methods or attributes cannot be inherited casually. Subclasses can extend the functions of parent classes, but cannot change the original functions of parent classes.

Operating environment: Windows 10 system, PHP 7.1 version, Dell G3 computer.

What is the concept of Richter substitution principle in PHP?

The Richter substitution principle tells us that replacing a base class object with its subclass object in software will not generate any errors or exceptions, and vice versa. If a software entity uses a subclass object, it may not be able to use the base class object.

Richter substitution principle is one of the important ways to implement the open-closed principle. Since the subclass object can be used wherever the base class object is used, the base class type is used to define the object as much as possible in the program, and the subclass type is determined at runtime, and the parent class object is replaced by the subclass object.

When using the Richter substitution principle, note that all methods of a subclass must be declared in the parent class, or that the subclass must implement all methods declared in the parent class. Try to design the parent class as an abstract class or interface, let the child inherit the parent class or implement the parent interface, and implement the method declared in the parent class. At runtime, the child instance replaces the parent class instance, so we can easily expand the system function without modifying the original child code. Adding new functions can be achieved by adding a new child.

A code to understand

The Richter substitution principle is a constraint on class inheritance. There are two interpretations of the Richter substitution principle:

1. You can't just inherit inappropriate classes with redundant methods or attributes. (Example 1)

2. Subclasses can extend the functionality of parent classes, but they cannot change the functionality of parent classes. (Example 2)

The Richter substitution principle contains several hidden meanings:

Subclasses can implement abstract methods of their parent classes, but they cannot override non-abstract methods of their parent classes.

2 Subclasses can add their own unique methods.

When a method of a subclass overloads a method of a parent class, the preconditions (i.e., parameters) of the method are looser than the input parameters of the parent class method.

When a child class's method implements an abstract method of its parent class, the postcondition of the method (i.e., the return value of the method) is stricter than that of the parent class.

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