Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:117445
Message-ID: <dc2e29b6-a8d6-23c8-0550-b34a8c1877e8@nunninger.info>
Date: Tue, 29 Mar 2022 15:33:41 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.7.0
Content-Language: en-US
To: internals@lists.php.net
References: <CAOfzkkwiSOP7v9JkEN9t2JPKPLSX+a3-ekBmSL02Hgw3Fmk71w@mail.gmail.com>
 <CA+hqhpdQUa9fjS=QRZgopTnwbzv=WW_9knbC+gO5AmNo3=s19g@mail.gmail.com>
 <CAPzBOBOZGokhdHZC_kYvS8r2fz6GR0TcomaG=7Babz355tXbjw@mail.gmail.com>
 <f19735d0-61c8-e9cb-d842-4cbab547a95b@gmail.com>
In-Reply-To: <f19735d0-61c8-e9cb-d842-4cbab547a95b@gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Subject: Re: [PHP-DEV] instance version of match ?
From: thomas@nunninger.info (Thomas Nunninger)

Hi,

Am 29.03.22 um 14:34 schrieb Rowan Tommins:
> On 29/03/2022 11:59, Robert Landers wrote:
>>          $object instanceof AnotherInterface => 'bar',
>>
>> We can see that `SomeInterface` will resolve the interface and not the
>> constant.
> 
> 
> Yeah, the instanceof operator is magic in that regard - it has a special 
> parsing rule to consume the next token and avoid it being evaluated as a 
> constant.
> 
> 
>> I think what they are proposing is that when the match is an object,
>> and the branches are class/interface/etc names, it should just do an
>> `instanceof` operation instead of a value-equals operation.
> 
> 
> That wouldn't work, because the type of value passed to match() can vary 
> at run-time, but you'd need to compile the expression one way or the other.
> 
> If it did work, it would be extremely confusing:
> 
> function example(string|object $input) {
>      return match($input)  {
>            SomeClass => 'found class',
>           SOME_CONSTANT => 'found constant',
>      };
> }
> var_dump( example(new SomeClass) );
> var_dump( example(SOME_CONSTANT) );
> 
> Do both of those matches succeed? What if I set `const SomeClass = 
> 'hello';`?
> 
> 
> So unfortunately we need some extra syntax to say that something should 
> be an instanceof check, and therefore a class name.

While I liked the intention of Karoly, I did not like the proposed magic.

Would it be an idea (and possible) to extend the syntax somehow like:

$result = match ($value) {
     instanceof MyObject => ...,
     >= 42 => ...,
     !== 5 => ...
};

to be equivalent to:

$result = match (true) {
     $value instanceof MyObject => ...,
     $value >= 42 => ...,
     $value !== 5 => ...
};


Regards
Thomas