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To: Jesse Schalken <me@jesseschalken.com>
Cc: Andrea Faulds <ajf@ajf.me>, PHP internals <internals@lists.php.net>
Date: Wed, 20 Apr 2016 11:46:46 +0200
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Subject: Re: [PHP-DEV] Re: Improving PHP's type system
From: johannes@schlueters.de (Johannes =?ISO-8859-1?Q?Schl=FCter?=)

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On Wed, 2016-04-20 at 17:57 +1000, Jesse Schalken wrote:
>=20
> With unions:
>=20
> function foo(Bar|string $b) {
>=20
>     if (is_string($b)) {
>         // ...
>     } else {
>         // I know $b is a Bar here. I don't need to check. :)
>     }
> }

I' still missing a real-life use case for this. There's no operation I
can come up with which works with an object or string.

Unions between object types should be handled via interface.

The only relevant union types I found till now are

  array | Traversable
  array | Countable

and eventually

  array | Offset[Get|Set]

The last one is a bit critical due to the fact that arrays are value
types, whereas objects are reference types so

   function ($a) {
       $a[] =3D 42;
   }

behaves notably differently between objects and arrays. So that case
might need some thinking. For the others instead of a generic union type
I'd prefer a special array-solution.

johannes

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