PHP Singleton mode (Singleton pattern) tutorial

Class DatabaseConnection { private static $db; private static $_handle = null; public static function get () { if (self:: $db = = null) { Echo __line__; Self:: $db = new DatabaseConnection (); } return self::$_handle; } Private Function __construct () { $dsn = ' Mysql://root:password@localhost/photos '; Self::$_handle = 123; } } Print ("Handle =". Databaseconnection::get (). " \ n "); Print ("Handle =". Databaseconnection::get (). " \ n "); ?> Copy Code 9Handle = 123 Handle = 123 [finished in 0.1s] Example 2,php single-case mode. !--? php class databaseconnection { public static function get () { static $db = null;//This changes the static member of Example 1 to a static variable if ($db = = null) { echo __line__; $db = new DatabaseConnection (); } return $db; } Private $_handle = null;//here will represent static removal of Example 1 Private Function __construc T () { $dsn = ' Mysql://root:password@localhost/photos '; $this->_handle =123; } //new method to get Private member $_handle public Function handle () { return $this-> ; _handle; } } print ("Handle =". Databaseconnection::get ()->handle (). " \ n "); Print ("Handle =".) Databaseconnection::get ()->handle (). " \ n "); ?> Copy Code 8Handle = 123 Handle = 123 [finished in 0.1s] These two examples of personal preference for the second four. Limit the number of instances that can be generated Class DatabaseConnection { public static function Get ($persistent _id=0) {//pass in an identity Static $db = Array ();//change here to array if (!array_key_exists ($persistent _id, $db)) { Echo __line__; $db [$persistent _id] = new DatabaseConnection (); } return $db [$persistent _id]; } Private $_handle = null; Private Function __construct () { $dsn = ' Mysql://root:password@localhost/photos '; $this->_handle = 123; } Here's a new way to get private member $_handle Public function handle () { return $this->_handle; } } Print ("Handle =". Databaseconnection::get (1)->handle (). " \ n "); Print ("Handle =". Databaseconnection::get (2)->handle (). " \ n "); Print ("Handle =". Databaseconnection::get (2)->handle (). " \ n "); ?> Copy Code 6Handle = 123 6Handle = 123 Handle = 123 [finished in 0.1s] supplement, using the static Statics method allows us to easily implement PHP singleton mode. Of course, you can also use global variable storage, but this approach is only available for smaller applications. In larger applications, you should avoid using global variables and use objects and methods to access resources.

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