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Date: Sat, 7 Nov 2020 20:46:06 +0100
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To: Eugene Sidelnyk <zsidelnik@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Union `&` operator
From: olleharstedt@gmail.com (=?UTF-8?Q?Olle_H=C3=A4rstedt?=)

https://wiki.php.net/rfc/intersection_types

2020-11-07 16:37 GMT+01:00, Eugene Sidelnyk <zsidelnik@gmail.com>:
> Yes.
> And I think it will be good if enforced by language.
>
> On Sat, Nov 7, 2020, 5:33 PM Olle H=C3=A4rstedt <olleharstedt@gmail.com> =
wrote:
>
>> 2020-11-07 15:12 GMT, Eugene Sidelnyk <zsidelnik@gmail.com>:
>> > When you follow ISP, you probably would have a lot of interfaces.
>> > Thus, client code may require an object to implement a bunch of
>> interfaces
>> > depending on functionality needed.
>> >
>> > Consider class `Bar`:
>> >
>> > ```php
>> >
>> > interface A {}
>> >
>> > interface B {}
>> >
>> > interface C {}
>> >
>> > interface D {}
>> >
>> > interface E {}
>> >
>> > class Bar implements A, B, C, D, E {
>> >     //
>> > }
>> > ```
>> >
>> >
>> > And some code, which uses `Bar`, but depends rather on interfaces,
>> > which
>> > functionality is actually needed:
>> >
>> > ```php
>> > function foo(A & B & E $object) {
>> >   // some work
>> >
>> >   var_dump($object);
>> > }
>> > ```
>> >
>> > It is currently feasable like this (ugly):
>> >
>> > ```php
>> > function foo(A $object) {
>> >   (function(B $object) {
>> >
>> >     (function(E $object) {
>> >
>> >         // some work
>> >
>> >         var_dump($object);
>> >
>> >     })($object);
>> >
>> >   })($object);
>> > }
>> > ```
>> >
>> > Or like this (more readable, but still):
>> >
>> > ```php
>> > function foo(A | B | E $object) {
>> >
>> >   if (!$object instanceof A) {
>> >     throw new \RuntimeException();
>> >   }
>> >
>> >   if (!$object instanceof B) {
>> >     throw new \RuntimeException();
>> >   }
>> >
>> >   if (!$object instanceof E) {
>> >     throw new \RuntimeException();
>> >   }
>> >
>> >   // some work
>> >
>> >   var_dump($object);
>> > }
>> > ```
>> >
>> > Another possible option is to create interface, which combines `A`,
>> > `B`,
>> > `E`, but in some cases it would lead us to interfaces explosion.
>> >
>> > This idea proposes to eliminate `instanceof` checks by introducing `&`
>> > union operator.
>> >
>>
>> You mean intersections? Psalm supports this notation.
>>
>