PHP single-instance mode implementation

/** * * User:jifei * DATE:2013-07-31 * time:23:19 */ /** * Class Singleton * Single-case mode, also known as the list mode, is a common software design mode. When applying this pattern, the class of the Singleton object must ensure that only one instance exists, * Fully embodies the thought of DRY (Don ' t Repeat yourself). * * The idea of implementing a singleton pattern is that a class can return an object with a reference (always the same) and a method that obtains the instance (must be a static method, usually using the name getinstance); * When we call this method, return this reference if the class holds a reference that is not empty, create an instance of the class if the class keeps a reference empty, and give the instance a reference to the class; * At the same time we define the constructor of the class as a private method, so that other code cannot instantiate the class's object by invoking its constructor, only the static method provided by the class to get the unique instance of the class. * * Application Scenario: A scenario that applies to only one instance of a class. Database connection, logging, shopping cart * Cons: PHP runs at the page level and cannot directly implement cross-page memory data sharing. */ Class Singleton { To save a private static member variable for a class instance private static $_instance; Private method of construction Private Function __construct () { Echo ' This is a constructed method; } Create an empty private __clone method to prevent the object from being cloned Private Function __clone () { } A singleton method for obtaining a unique instance object public static function getinstance () { if (! ( Self::$_instance instanceof Self)) { Instanceof is used to detect the dependencies of an object to a class, is_subclass_of whether the class belongs to a subclass of the class Self::$_instance = new self (); } return self::$_instance; } Test Public Function test () { Echo 123; } } $a = singleton::getinstance (); $a->test (); Echo Php_eol; $b = Singleton::getinstance (); Construction method is not executed on second call $b->test (); Echo Php_eol; $c =new Singleton (); Because the construction method is private, this will be an error. $d =clone $a; Clone object error Copy Code

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