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<?php class Foo { private const string PREFIX = "Hello. "; private static string $prefix = "Hello, "; private static function prefix(): string { return "Hello, "; } public function greetFunc(string $to): string { return self::prefix() . $to . "!"; // OK, but unnecessary LSB } public function greetVar(string $to): string { return self::$prefix . $to . "!"; // OK, but unnecessary LSB } public function greetConst(string $to): string { return static::PREFIX . $to . "!"; // It should be self::PREFIX. } } class Bar extends Foo { } echo (new Bar())->greetFunc("World") . PHP_EOL; echo (new Bar())->greetVar("World") . PHP_EOL; // echo (new Bar())->greetConst("World") . PHP_EOL; // Error! Referencing undefined Bar::PREFIX... class Buz extends Foo { protected static string $prefix = "Hi, "; protected static function prefix(): string { return "Hi, "; } } echo (new Buz())->greetFunc("World") . PHP_EOL; // No! private function was actually overridden!! echo (new Buz())->greetVar("World") . PHP_EOL; // No! private property was actually overridden!!