php 5.3 subclass singleton
for the "Late Static Bindings" imported by php from version 5.3,(http://php.net/manual/en/language.oop5.late-static-bindings.php)singleton patterns:
<?php
class Singleton {
static private $instance;
protected static function create(){
if(is_null(self::$instance)){
self::$instance = new self();
}
return self::$instance;
}
static public function instance(){
return static::create(); //!important to use static
}
public function __construct(){echo 1;}
}
class MySingleton extends Singleton {
static private $instance; //in subclass,explicitly declare this and the method below
protected static function create(){
if(is_null(self::$instance)){
self::$instance = new self();
}
return self::$instance;
}
}
class YourSingleton extends Singleton {
static private $instance;
protected static function create(){
if(is_null(self::$instance)){
self::$instance = new self();
}
return self::$instance;
}
}
class ThirdSingleton extends MySingleton {
static private $instance;
protected static function create(){
if(is_null(self::$instance)){
self::$instance = new self();
}
return self::$instance;
}
}
echo get_class(Singleton::instance());//=>Singleton
echo get_class(MySingleton::instance());//=> MySingleton
echo get_class(MySingleton::instance());//=> MySingleton
echo get_class(YourSingleton::instance());//=>YourSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
a code-less but confusable style:
<?php
class Singleton {
static private $instance;
static public function instance(){
static $instance = null;//should not add self:: or static:: here
return $instance ?: $instance = new static;
}
public function __construct(){echo 1;}
}
class MySingleton extends Singleton {
}
class YourSingleton extends Singleton {
}
class ThirdSingleton extends MySingleton {
}
echo get_class(Singleton::instance());//=>Singleton
echo get_class(MySingleton::instance());//=> MySingleton
echo get_class(MySingleton::instance());//=> MySingleton
echo get_class(YourSingleton::instance());//=>YourSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
the following maybe the best one:
class Singleton {
static protected $instance; //should not be private
static public function instance(){
if(is_null(static::$instance)){ //important to use static
static::$instance = new static();
}
return static::$instance;
}
public function __construct(){echo 1;}
}
class MySingleton extends Singleton {
static protected $instance; //must explicitly declared
}
class YourSingleton extends Singleton {
static protected $instance;
}
class ThirdSingleton extends MySingleton {
static protected $instance;
}
echo get_class(Singleton::instance());//=>Singleton
echo get_class(MySingleton::instance());//=> MySingleton
echo get_class(MySingleton::instance());//=> MySingleton
echo get_class(YourSingleton::instance());//=>YourSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
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