A major behavior i wanted to discuss is how should sealed interfaces work, and specially around `Throwable` which is currently sealed to only `Error` and `Exception`, but allows other interfaces to extend it, and other classes to implement it as long as they extend `Error` or `Exception` ( or another class that does so ).
As per the current proposal, if `Throwable` is to be declared `sealed`, permitting only `Error` and `Exception`, it won't be possible to extend it, resulting in a major BC-break, considering that too many libraries extend this interface in their own `ExceptionInterface`. To work around this, there's two solution: 1. don't declare `Throwable` sealed and keep it as a special case. 2. interfaces declared sealed, can be extended by other interfaces, however, classes that implement either the sealed interface directly, or via another interface, have to extend one of the classes the sealed interface permits. The second solution will allow declaring `Throwable` sealed, and would bring complete consistency between internally sealed symbols, and user land, without any BC breaks, and IMHO, it doesn't hurt as at the end, no one will be able to implement `Throwable` without extending the permitted classes. Note: with the second solution, if an interface is sealed and permits only 2 classes which are final, and you extend that interface into another, there's no way you can actually implement your new interface, and i will be as if you just declared a final interface. ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Saturday, April 24, 2021 11:55 AM, Saif Eddin Gmati <azj...@protonmail.com> wrote: > Hello Internals, > > I'm sending this email to open discussion about sealed classes, interfaces, > and traits feature for PHP 8.1. > > I have create a Draft RFC here: https://wiki.php.net/rfc/sealed_classes > > A major concern for few people have been the syntax, in which it introduces 2 > new keywords into the languages, therefor, i have added a section about > alternative syntax which could be used to avoid this problem. > > Regards, > > Saif.
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