<?php
class A
{
public static $instance;
public static function getInstance() {
if (self::$instance === null) {
self::$instance = new static();
}
return static::$instance;
}
}
class B extends A
{
public static $instance;
}
class C extends A
{
}
echo get_class(A::getInstance()) . PHP_EOL;
echo get_class(B::getInstance()) . PHP_EOL; //As you can see, a new B is instantiated here, because B::$instance is a priority over A::$instance.
echo get_class(A::getInstance()) . PHP_EOL;
A::$instance = null;
echo PHP_EOL;
echo get_class(A::getInstance()) . PHP_EOL;
echo get_class(C::getInstance()) . PHP_EOL; //But here, there is no C::$instance, so let's check the A::$instance which is not empty.
echo get_class(A::getInstance()) . PHP_EOL;
A
Fatal error: Uncaught TypeError: get_class(): Argument #1 ($object) must be of type object, null given in /in/qZZWP:25
Stack trace:
#0 {main}
thrown in /in/qZZWP on line 25
Process exited with code 255.