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Date: Wed, 20 Apr 2016 20:11:33 +1000
Message-ID: <CAF1yvATYTn+tWYk12WeqysAWVRH7G+WCz5WwgMTAZgNq2BSJZg@mail.gmail.com>
To: =?UTF-8?Q?Johannes_Schl=C3=BCter?= <johannes@schlueters.de>
Cc: Andrea Faulds <ajf@ajf.me>, PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001a113ea5f083ee130530e7d189
Subject: Re: [PHP-DEV] Re: Improving PHP's type system
From: me@jesseschalken.com (Jesse Schalken)

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   1. I have a function that converts values to SQL which have SQL
   equivalents, including decimal values represented by a special Decimal
   class. It accepts int|string|bool|null|float|Decimal.
   2. I have a class Expr which represents an expression in SQL.
   Expressions can be composed of other expressions, and of literal values,=
 so
   the constructors for Exprs accept int|string|bool|null|float|Decimal|Exp=
r.
   3. I have a function that converts values to JSON that can be reliably
   converted back into their original. It accepts int|string|bool|null|floa=
t.
   4. I have a function that returns the first key in an array (or throws
   an exception if empty). It returns int|string.
   5. I have a function that returns a value for a key in an array, and
   removes the key. The type of the key is things that are valid array keys
   (int|string|bool|null IIRC).
   6. I have a set of functions which operates on numbers. They accept
   int|float.
   7. All the PHP functions which say "returns ... or FALSE on failure"
   have their correct return type as T|false (where T is the return value o=
n
   success) (or T|bool is "false" is not an allowed type).
   8. Nullability is nothing but a special case of union type with T|null.

If you need more examples, search some PHP codebases for PHPDoc blocks with
union types with a regex, like "@(param|var)\s*(\$\w+\s*)?\w+\|".


On Wed, Apr 20, 2016 at 7:46 PM, Johannes Schl=C3=BCter <johannes@schlueter=
s.de>
wrote:

> On Wed, 2016-04-20 at 17:57 +1000, Jesse Schalken wrote:
> >
> > With unions:
> >
> > function foo(Bar|string $b) {
> >
> >     if (is_string($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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