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 <57192F87.4080902@fleshgrinder.com>
Date: Fri, 22 Apr 2016 11:42:34 +0200
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To: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Nullable Types
From: quim@kalpe.com (Quim Calpe)

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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.

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