Re: [RFC] Nullable Types

On Thu, Apr 21, 2016 at 9:52 PM, Fleshgrinder <php@fleshgrinder.com> wrote: > On 4/21/2016 1:00 PM, Lin Yo-An wrote: > > I think this is not to make PHP like Java, and it totally makes sense - > > Nullable should be a type of a type instead of a state. In Haskell it's > > named Maybe or Option, and It's better than NullPointerException. > > > > Here is a discussion from Haskell community: > > > > https://mail.haskell.org/pipermail/haskell-cafe/2011-April/091269.html > > > > Why is it /better/? > > final class None {} > > final class Some { > > public $value; > > public function __construct($value) { > $this->value = $value; > } > > } > > final class Maybe { > > private static $none; > > private $value; > > private function __construct($value) { > $this->value = $value; > } > > public static function NOTHING() { > if (self::$nothing === null) { > self::$nothing = new Nothing(); > } > return new static(self::$nothing); > } > > public static function SOME($value) { > return new static(new Some($value)); > } > > public function hasSome(): bool { > return $this->value !== static::$none; > } > > public function isNone(): bool { > return $this->value === static::$none; > } > > public function unwrap() { > if ($this->value === static::$none) { > trigger_error('NullPointerException', E_USER_ERROR); > } > return $this->value->value; > } > > } > > // ---------------------------------------- > > function f1(): Option {} > > $x = f1(); > if ($x->hasSome()) { > echo $x->unwrap(); // 42 > } > > $x = f1(); > if ($x->isNone()) { > echo -1; > } > > echo f1()->unwrap(); // error: NullPointerException :P > > // ---------------------------------------- > > function f2(): ?int {} > > $y = f2(); > if (isset($y)) { > echo $y; // 42 > } > > $y = f2(); > if ($y === null) { > echo -1; > } > > echo f2(); // null > > You can easily build your own Option or Maybe and add the additional > bookkeeping to your runtime but it will not make your program more > secure or anything. It just adds more method calls and makes it more > verbose. > > You can already use static code analyzers to detect if null is being > ignored in your code, however, right now they mainly have to rely on > PhpDoc that is often not properly documented. Adding an explicit syntax > to PHP for documentation would make PhpDoc obsolete and allow static > code analyzers to perform their job better and PHP to error out during > runtime if something else is being returned. > > Honestly, null is not our problem. Every language has its null, just > because they wrap it or rename it does not make null suddenly vanish > from the universe. :P > > -- > Richard "Fleshgrinder" Fussenegger > > IMHO, the point of Optional types is the intention, if you get an Option<Foo> from a method, you have to deal with a None branch. Of course you can just unwrap and go on, but it's a developer decision to do that, not an oversight as using a Foo|null (or ?Foo) as an object directly.