Re: [RFC] $this return type

On 07.09.2021 at 15:02, Andreas Heigl wrote: > On 07.09.21 12:28, Nikita Popov wrote: > >> 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 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