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@ 2015-10-09T23:07:18Z

<?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;

Output for git.master, git.master_jit, rfc.property-hooks: 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.

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2020-03-21 RFC: Is_Literal - declined
2020-12-04 Enumerations - included in PHP 8.1
2018-06-15 Typed Properties v2 - implemented in PHP 7.4
2016-08-12 Object typehint - included in PHP 7.2
2016-08-14 Arrow functions - withdrawn
2016-05-29 array_change_keys() - withdrawn
2016-04-19 Lexical scope support for anonymous classes - suspended
2016-04-17 Functional Interfaces - declined
2016-03-16 Typed Properties - superseded in favor of Typed Properties 2.0
2015-08-27 Callable Prototypes - declined
2015-05-01 Short Closures - declined / withdrawn in favor of Arrow Functions
2015-02-18 Scalar type hints v5 - included in PHP 7
2015-02-14 Union Types - declined
2013-09-22 Anonymous classes - included in PHP 7

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