PHP singleton pattern (Singleton Pattern) example 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" );
?>

9Handle = 123 Handle = 123 [Finished in 0.1s]

Example 2, PHP singleton mode.

class DatabaseConnection
{
 public static function get()
 {
 static $db = null;//Change the static members of Example 1 into static variables here
 if ( $db == null ){
 echo __LINE__;
 $db = new DatabaseConnection();
 }
 return $db;
 }

 private $_handle = null;//This will represent the static removal of Example 1

 private function __construct()
 {
 $dsn = 'mysql://root:password@localhost/photos';
 $this->_handle =123;
 }
 //A new method to get the private member $_handle is added here
 public function handle()
 {
 return $this->_handle;
 }
}

print( "Handle = ".DatabaseConnection::get()->handle()."n" );
print( "Handle = ".DatabaseConnection::get()->handle()."n" );
?>

8Handle = 123 Handle = 123 [Finished in 0.1s] Of these two examples, my personal preference is the second one Four. Limit the number of instances that can be generated

class DatabaseConnection {
 public static function get($persistent_id=0) {//Pass in an identifier
 static $db = array();//Change to array here
 if ( !array_key_exists($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;
 }
 //Add private member $_handle here Method
 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" );
?>

6Handle = 123 6Handle = 123 Handle = 123 [Finished in 0.1s] In addition, using static method allows us to easily implement PHP's singleton mode. Of course it is also possible to use global variable storage, but this approach is only suitable for smaller applications. In larger applications, avoid using global variables and use objects and methods to access resources.