The difference between php classes and functions

Object-oriented programming (OOP) has introduced quite a few features, making programming more complex. Encapsulation, inheritance, and polymorphism are the three elements of OOP, which are not found in functions in procedures.

is embodied in:

1. Encapsulation: class/interface/public/protected/private

2. Inheritance: extends/implements (recommended learning: PHP Programming from entry to proficiency)

3. Polymorphism: method rewriting/method overloading

New New variable scopes have been added to classes and interfaces, that is, the code blocks in classes and interfaces have a scope that functions do not have.

In this scope, you can define variables and functions as members of classes and interfaces, and support the use of public/protected/private keywords to control access to these members. For example, public means that external access is allowed, and protected means that external access is allowed. Access is allowed for the class and its subclasses, and private means access is only allowed within the class.

Classes must be declared with the keyword class. Classes are composed of attributes and methods. Objects can be instantiated and classes can be inherited. Generally, classes are used in object-oriented programming; functions have no attributes and generally Used in process-oriented, written to solve a specific problem.

Moreover, OOP also introduces the polymorphic features of method rewriting and method overloading, namely:

Method rewriting: the parameter list is the same, the method body Different.

Method overloading: different parameter list, different method body.

Method overriding relies on inheritance, which means that the method of the subclass overrides the method of the parent class, and the method name and parameter list are required to be the same.

Method overloading does not rely on inheritance. It is two or more methods with the same name in the same class, with different parameter lists.

It should be noted that inherited and overridden methods only Access permissions can be maintained or enlarged, but cannot be reduced.

For example, it is feasible for a parent class's protected method to be overloaded as public in a subclass.

In PHP, because multiple A method with the same name, so method overloading like C/Java is not supported.

But PHP provides magic methods (__call, __callStatic) for indirect method overloading.

Method rewriting in PHP does not require the same parameters.

PHP does not support multiple inheritance (inheriting multiple parent classes), but it can implement multiple interfaces, and you can also use trait attributes to indirectly support multiple inheritance.

Some people think that inheritance will increase the coupling between subclasses and parent classes, so they oppose inheritance. Some new programming languages, such as Go, do not support inheritance directly, but use combination to replace inheritance. For example, dependency injection, in essence It is also a combination of ideas, used to achieve decoupling. In PHP, you can final modify a class to prohibit this class from being inherited.

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