Extending singletons in PHP

Question

I\'m working in a web app framework, and part of it consists of a number of services, all implemented as singletons. They all extend a Service class, where the singleton behavio

Answer 1

I have found a good solution.

the following is my code

abstract class Singleton
{
    protected static $instance; // must be protected static property ,since we must use static::$instance, private property will be error

    private function __construct(){} //must be private !!! [very important],otherwise we can create new father instance in it's Child class 

    final protected function __clone(){} #restrict clone

    public static function getInstance()
    {
        #must use static::$instance ,can not use self::$instance,self::$instance will always be Father's static property 
        if (! static::$instance instanceof static) {
            static::$instance = new static();
        }
        return static::$instance;
    }
}

class A extends Singleton
{
   protected static $instance; #must redefined property
}

class B extends A
{
    protected static $instance;
}

$a = A::getInstance();
$b = B::getInstance();
$c = B::getInstance();
$d = A::getInstance();
$e = A::getInstance();
echo "-------";

var_dump($a,$b,$c,$d,$e);

#object(A)#1 (0) { }
#object(B)#2 (0) { } 
#object(B)#2 (0) { } 
#object(A)#1 (0) { } 
#object(A)#1 (0) { }

You can refer http://php.net/manual/en/language.oop5.late-static-bindings.php for more info