# [RFC] $this return type - Thread: https://externals.io/message/115986 - Original archive: https://news-web.php.net/php.internals/115986 - Started by Nikita Popov on 2021-09-07T10:28:32+00:00 - Messages: 9 - RFC: Static return type (Implemented (PHP 8.0)) — https://externals.io/rfc/static_return_type.md - Reply by email to internals@lists.php.net - More for agents: search with https://externals.io/search.md?q={query} · RFCs at https://externals.io/rfc.md · JSON API at https://externals.io/api · documentation at https://externals.io/llms.txt --- ## #115986 — Nikita Popov — 2021-09-07T10:28:32+00:00 URL: https://externals.io/message/115986#115986 Hi internals, I'd like to pick up a loose thread from the future scope of the https://wiki.php.net/rfc/static_return_type RFC, the $this return type for fluent APIs: https://wiki.php.net/rfc/this_return_type I have some reservations about this (which basically come down to $this not being a proper "type", so should it be in the type system?) but I can see the practical usefulness, so I think it's worth discussing this. Regards, Nikita --- ## #115991 — michal.brzuchalski@gmail.com — 2021-09-07T11:38:40+00:00 URL: https://externals.io/message/115986#115991 · In reply to: #115986 Hi Nikita, wt., 7 wrz 2021 o 12:29 Nikita Popov napisał(a): > Hi internals, > > I'd like to pick up a loose thread from the future scope of the > https://wiki.php.net/rfc/static_return_type RFC, the $this return type for > fluent APIs: > > https://wiki.php.net/rfc/this_return_type > > I have some reservations about this (which basically come down to $this not > being a proper "type", so should it be in the type system?) but I can see > the practical usefulness, so I think it's worth discussing this. If the aim of $this return type is to force and check the return $this why would we still need/require return statement to be obligatory? Does that make sense to assume at the end of function flow the return $this; statement to be present by default if the return type is not an union etc.? Cheers, -- Michał Marcin Brzuchalski --- ## #115992 — Andreas Heigl — 2021-09-07T13:02:28+00:00 URL: https://externals.io/message/115986#115992 · In reply to: #115986 Hey Nikita > Hi internals, > > I'd like to pick up a loose thread from the future scope of the > https://wiki.php.net/rfc/static_return_type RFC, the $this return type for > fluent APIs: > > https://wiki.php.net/rfc/this_return_type > > I have some reservations about this (which basically come down to $this not > being a proper "type", so should it be in the type system?) but I can see > the practical usefulness, so I think it's worth discussing this. > > Regards, > Nikita If we allow a $this (let's keep the actual naming out for the moment) as a returntype to clarify that it has to be the same instance that is returned, I would also either expect that the returntype 'self' does explicitly *not* allow the same instance to be returned. As that would be a huge BC break I would on the other hand also think that we should implement a returntype "!$this" to explicitly state that the contract here returns *not* the current instance but a new one. That way a lot of immutable contracts could be made more clear. What'S your or others idea regarding that? Cheers Andreas -- ,,, (o o) +---------------------------------------------------------ooO-(_)-Ooo-+ | Andreas Heigl | | mailto:andreas@heigl.org N 50°22'59.5" E 08°23'58" | | https://andreas.heigl.org | +---------------------------------------------------------------------+ | https://hei.gl/appointmentwithandreas | +---------------------------------------------------------------------+ --- ## #115993 — Christoph M. Becker — 2021-09-07T13:24:02+00:00 URL: https://externals.io/message/115986#115993 · In reply to: #115992 > > > > […] > > If we allow a $this (let's keep the actual naming out for the moment) as > a returntype to clarify that it has to be the same instance that is > returned, I would also either expect that the returntype 'self' does > explicitly *not* allow the same instance to be returned. As that would > be a huge BC break I would on the other hand also think that we should > implement a returntype "!$this" to explicitly state that the contract > here returns *not*  the current instance but a new one. That way a lot > of immutable contracts could be made more clear. > > What'S your or others idea regarding that? In my opinion, we should not muddy the waters here. $this is not a type. Instead we should consider to head for a more general solution, namely suporting post-conditions, i.e. assertions which are part of the function/method signature. But that would certainly be the topic of another RFC. Christoph --- ## #115994 — Sebastian Bergmann — 2021-09-07T13:27:37+00:00 URL: https://externals.io/message/115986#115994 · In reply to: #115986 Am 07.09.2021 um 12:28 schrieb Nikita Popov: > I have some reservations about this (which basically come down to $this not > being a proper "type", so should it be in the type system?) but I can see > the practical usefulness, so I think it's worth discussing this. I am not conviced that there is enough value in this to introduce syntax for it, but if at all, then please not "$this" as the name for a type. Off the top of my head, I think that "same" could make sense. --- ## #116024 — flaviohbatista@gmail.com — 2021-09-09T14:26:20+00:00 URL: https://externals.io/message/115986#116024 · In reply to: #115994 On Tue, Sep 7, 2021 at 10:27 AM Sebastian Bergmann wrote: > Am 07.09.2021 um 12:28 schrieb Nikita Popov: > > […] > not > > […] > > I am not conviced that there is enough value in this to introduce syntax > for it, but if at all, then please not "$this" as the name for a type. > > Off the top of my head, I think that "same" could make sense. > > -- > > To unsubscribe, visit: https://www.php.net/unsub.php > > Hi all, I'm sorry if I'm being naive, or simply put dumb, but the main difference that we're trying to achieve with having "$this" (or variations of it) as a valid return type as opposed to simply using "self" is to ensure that the underlying code is actually doing a "return $this" rather than returning any other valid "self" instance (such as "return new self();")? -- Atenciosamente, Flávio Heleno --- ## #116025 — Mike Schinkel — 2021-09-09T14:47:26+00:00 URL: https://externals.io/message/115986#116025 · In reply to: #116024 > > > On Tue, Sep 7, 2021 at 10:27 AM Sebastian Bergmann > wrote: > > > […] > Hi all, > > I'm sorry if I'm being naive, or simply put dumb, but the main difference > that we're trying > to achieve with having "$this" (or variations of it) as a valid return type > as opposed to simply > using "self" is to ensure that the underlying code is actually doing a > "return $this" rather > than returning any other valid "self" instance (such as "return new > self();")? So a *mutable* fluent style vs. an *immutable* fluent style? -Mike --- ## #116026 — Ben Ramsey — 2021-09-09T15:00:03+00:00 URL: https://externals.io/message/115986#116026 · In reply to: #116025 > > > > […] > > So a *mutable* fluent style vs. an *immutable* fluent style? > > -Mike For clarity, in comparing to `self` and `static`… `self` : the return value must be an instance of the same class that sets this type declaration `static` : the return value must be an instance of the same class that calls the method with this type declaration `$this` : the return value must be the same instance as the instance that calls the method with this type declaration Cheers, Ben --- ## #116098 — Nicolas Grekas — 2021-09-19T13:39:01+00:00 URL: https://externals.io/message/115986#116098 · In reply to: #115986 Hi Nikita Hi internals, > > I'd like to pick up a loose thread from the future scope of the > https://wiki.php.net/rfc/static_return_type RFC, the $this return type for > fluent APIs: > > https://wiki.php.net/rfc/this_return_type > > I have some reservations about this (which basically come down to $this not > being a proper "type", so should it be in the type system?) but I can see > the practical usefulness, so I think it's worth discussing this. > Thank you so much for the RFC. I'm really looking forward to being able to use $this as a return type. > On a dataset of 2k composer packages, @return $this occurs 29k times, while @return static is used 38k times This is really good to know. It makes it pretty clear to me that being able to declare $this as a return value would be valuable to many projects! As far as my experience is concerned, I tried switching from the `@return $this` annotation to `function (): static`, which is the closest approximation currently supported by the engine, when I realized that this would loosen the semantics of the corresponding interfaces and kinda force ppl to deal with the return value while this doesn't make sense in fluent-style APIs. I therefore kept the annotation in place and I'm now looking forward to being able to write this declaration using native syntax - with the added benefit of having it enforced by the engine. About the syntax, I think the one proposed in the RFC is crystal clear. I've been used to seeing the "$" symbol when reading `@return $this`, and this just makes sense, past the first surprise. I also think that using "this" (without the dollar) could too easily be confused with something that means our "static" (esp. considering that TypeScript uses "this" in place of our "static".) I'm reading in responses that $this is not a type, but I fail to understand how that makes it an argument against the RFC. Neither false is a type, and null is both a type and a value. Yet we have them because they provide clear added value. Having $this could benefit 29k times the top 2k packages. It doesn't look like a niche use case! As you might have understood, I support the RFC and would vote for it as is personally! Nicolas