You must be careful when getting static property of extended class from parent class, in example below you can see that using property_exists (method getA2) instead of isset with static keyword (method getA1) to check if the static property exist gives much more intuitive result:
<?php
class Foo
{
public static string $A;
public static function init() {
return static::class;
}
public static function getA1() {
if (!isset(static::$A)) {
static::$A = static::class;
}
return static::$A;
}
public static function getA2() {
if (property_exists(static::class, 'A')) {
static::$A = static::class;
}
return static::$A;
}
}
class Bar extends Foo {}
$foo = new Foo();
echo $foo->getA1();
echo $foo->getA2();
echo $foo->getA1();
$bar = new Bar();
echo $bar->getA1();
echo $bar->getA2();
echo $bar->getA1();
?>
Output:
Foo
Foo
Foo
Foo
Bar
Bar
Notice how $bar->getA1() returns "Foo" instead of "Bar" that many people would expect to see.
