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Date: Sat, 7 Nov 2020 15:33:21 +0000
Message-ID: <CAJpLVh29eDnJV=bQz97xdpbRsUqJAkrnkArkymC0EFqJpeaMxg@mail.gmail.com>
To: Eugene Sidelnyk <zsidelnik@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
Content-Type: text/plain; charset="UTF-8"
Subject: Re: [PHP-DEV] Union `&` operator
From: olleharstedt@gmail.com (=?UTF-8?Q?Olle_H=C3=A4rstedt?=)

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.