Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:108070
To: Andreas Hennings <andreas@dqxtech.net>,
 Nikita Popov <nikita.ppv@gmail.com>
Cc: Rowan Tommins <rowan.collins@gmail.com>,
 php internals <internals@lists.php.net>
References: <CAF+90c-vPOmHzjoDFNi3m+iTgfz6dJep1DAHuCFcQDctjeEJMg@mail.gmail.com>
 <e30686d8-4836-4403-851f-06f296ccbafd@www.fastmail.com>
 <CAH0Uv3Hp2GUwKX0YOs-E1-1W9LkXzc71pBsvNQRnRvNicw=YdQ@mail.gmail.com>
 <CALKiJKqTpuyUQ3gu=hVZumxdjut-9HiRBXLy9DRNf41bihe=pw@mail.gmail.com>
 <CAF+90c8fuNLUy4drT1F84E6=WRe44VD9Zq6T+4bT+41BfD5q+Q@mail.gmail.com>
 <CAH0Uv3EZRVtV0ZxV5BBRMo8SVvzB9=g9D4m6kSySApHqFZH9Fg@mail.gmail.com>
Message-ID: <d477b5d8-e7a5-4016-43e7-ba3da1a210c5@xs4all.nl>
Date: Thu, 9 Jan 2020 20:53:26 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.2.2
MIME-Version: 1.0
In-Reply-To: <CAH0Uv3EZRVtV0ZxV5BBRMo8SVvzB9=g9D4m6kSySApHqFZH9Fg@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Subject: Re: [PHP-DEV] [RFC] Static return type
From: d.takken@xs4all.nl (Dik Takken)

On 09-01-2020 17:52, Andreas Hennings wrote:
> On Thu, 9 Jan 2020 at 16:31, Nikita Popov <nikita.ppv@gmail.com> wrote:
> 
>> On Thu, Jan 9, 2020 at 4:06 PM Rowan Tommins <rowan.collins@gmail.com>
>> wrote:
>>
>> An argument could be made that $this does also specify a certain contract
>> to the caller: That the API may be used fluently or not without change in
>> functionality. That is
>>
>>     $foo->setBar();
>>     $foo->setBaz();
>>
>> must be strictly equivalent to
>>
>>     $foo
>>        ->setBar()
>>        ->setBaz()
>>     ;
>>
>> The same is not the case for a plain "static" type. In fact, I think that
>> for all other uses of "static" outside of fluent interfaces, not using the
>> return value would be a programming error.
>>
>> But still, this kind of contract is not a type-system contract, and I'm not
>> sure it's a good idea to mix other types of API contracts into the type
>> system in this fashion.
>>
> 
> We currently don't have another "system" where this kind of info could be
> specified.

How about:

  public fluent function doWhatever(): static

Perhaps this could be introduced at some point in the future to enforce
returning $this.

> And in this case, $this also implies static, so if we would use whichever
> other system to specify $this, the type hint "static" would become
> redundant.
> 
> "@return $this" is common in phpdoc (*) since a while, and so far I have
> not seen any problems with it.
> 
> If we ask "where does this lead?", one natural next step might be to
> specifically say that the return type is the same type, but NOT $this.
> So, a promise that we really get a new object which we can modify without
> changing the original object.
> 
> I don't know how we would express this. Perhaps ": clone", but this would
> be too specific imo, because whether it is a clone is an implementation
> detail.

Maybe ": new" ?

Regards,
Dik Takken