When using !(self::$_instance instanceof self) why does this fail to work

Question

I recently had written some code to deal with instantiating a object, assigning a object and some data to the objects properties and then perform a call to a method in order to do something.

But when running the code in a loop, it failed to work and I couldn't understand why, my sample code is :-

Controller functionality :-

$arrayOfObjects = SomeClass::getItems();
foreach ($arrayOfObjects as $object) {
    SomeOtherObject::getInstance($object, time())->run();
}

SomeOtherObject::getInstance() :-

public static function getInstance($object, $timestamp) {
    if (!(self::$_instance instanceof self)) {
        self::$_instance = new self($object, $timestamp);
    }
    return self::$_instance;
}

private function __contruct($object, $timestamp) {
    $this->_theObjectPassed = $object;
    $this->_theTimestampPassed = $timestamp;
}

What baffled me was that the run method on the SomeOtherObject wasn't doing what I expected. When I added debugging within the loop i.e. outputting a getName() method on the $object I got the same one for each item in the loop.

When changing the way I construct the object to the following (instead of getInstance()) it worked :-

$someOtherObject = new SomeOtherObject($object, time());
$someOtherObject->run();

I'm guessing it has something to do with the way the getInstance method works and how it is checking but wondered if anyone could explain it.

Thanks

Answer 1

Looks like you misunderstood static variables. A static variable will be created / initialized once per class and not once per object.

Your if statement will be true only the first time getInstance() is called , when $_instance hasn't been initialized. A reference to a new instance of SomeOtherObject will be assigned to it then.

On all following calls the if will return false and the existing $_instance will just being returned instead of creating a new one.

Remove the if statement from the getInstance() method:

public static function getInstance($object, $timestamp) {
    return new self($object, $timestamp);
}