How to implement in php that a class can only be loaded once

php method to implement a class that can only be loaded once: 1. Create a php sample file; 2. Create a private static variable to store the class instance. This variable must be private to ensure that it can only be loaded once. Access it within the class; 2. Create a private constructor to prevent the class from being instantiated; 3. Create a public static method to obtain an instance of the class.

Operating system for this tutorial: Windows 10 system, php8.1.3 version, Dell G3 computer.

In PHP, you can implement the method of loading a class file once by using the "singleton" mode.

The specific steps are as follows:

1. Create a private static variable to store class instances. The variable must be private to ensure that it can only be accessed within the class and not directly created instances outside.

class SingletonClass {
    private static $instance;
}

2. Create a private constructor to prevent the class from being instantiated. If you directly try to instantiate a singleton class, a Fatal Error will be thrown.

private function __construct() {
   // Initialization code here...
}

3. Create a public static method to obtain an instance of the class. Check if the instance already exists. If it does not exist, create a new instance and return it. If it exists, the existing instance is returned directly.

public static function getInstance() {
    if (!isset(self::$instance)) {
       self::$instance = new SingletonClass();
    }
    return self::$instance;
}

This class will only be loaded once, because the same instance is returned every time the getInstance method is called. This method ensures that only one instance of a singleton class runs in memory, avoiding conflicts and data inconsistencies between multiple class instances.

Note that since an instance always exists, updates or modifications to it must always be handled with caution.

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