Three Common Design Patterns in PHP

First of all, let's look at the singleton pattern

The so-called singleton pattern refers to the existence of only one instance of this class in the application.

The singleton pattern is usually used in instances that allow only database access objects, thus preventing multiple database connections from being opened.

A singleton class should include the following points:

Different from ordinary classes, singleton classes cannot be instantiated directly but can only be instantiated by themselves. Therefore, to achieve such a restricted effect, the constructor must be marked as private.

To make the singleton class not be instantiated directly and have an effect, it must provide such an instance. Therefore, it is necessary for the singleton class to have a private static member variable that can save the class instance and a corresponding public static method that can access the instance.

In PHP, to prevent the cloning of singleton class objects from breaking the above implementation form of the singleton class, an empty private __clone() method is usually provided for the base.

The singleton pattern ensures that a class has only one instance and that it instances itself and provides this instance to the entire system.

The singleton pattern is a common design pattern. In computer systems, thread pools, caches, log objects, dialog boxes, printers, database operations, and graphics driver programs are often designed as singletons.

The singleton pattern is divided into3Types: Lazy initialization singleton, eager initialization singleton, registration singleton.

The singleton pattern has the following3Characteristics:

1. There can only be one instance.

2. It must create this instance itself.

3. It must provide this instance to other objects.

Then why use the PHP singleton pattern?

One of the main application scenarios of PHP is the scenario where applications interact with databases. There will be a large number of database operations in an application, and using the singleton pattern can avoid a large number of new operations for the behavior of connecting to the database through the database handle. Because each new operation will consume system and memory resources.

In the past project development, the situation before using the singleton pattern is as follows: incomplete...

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