Req #80921 [Com]: allow parameter type hints for poorly typed interface methods

Edit report at https://bugs.php.net/bug.php?id=80921&edit=1 ID: 80921 Comment by: smiley at chillerlan dot net Reported by: smiley at chillerlan dot net Summary: allow parameter type hints for poorly typed interface methods Status: Wont fix Type: Feature/Change Request Package: Class/Object related PHP Version: Irrelevant Block user comment: N Private report: N New Comment: Thank you for the quick reply! I understand the general problem with LSP, however, the problem i see with PHP is that (scalar) type hints didn't exist before 7.0 and a lot of userland interfaces therefore technically cannot adhere to LSP (even though types may be declared in docblocks). In the example case of PSR-7, implementors are left with countless type checks that could be avoided if it was possible to add type hints. Previous Comments: ------------------------------------------------------------------------ [2021-03-30 20:52:28] tiffany@php.net Changing parameter types to allow a more specific type opposes the Liskov Substitution Principle. Contravariance states parameter types of a child class method can be less specific than its parent class method. https://www.php.net/manual/en/language.oop5.variance.php ------------------------------------------------------------------------ [2021-03-30 20:51:50] requinix@php.net No parameter type means "mixed", as in any type is accepted. Allowing a child class like StronglyTypedClass to be more restrictive about its *parameter types* violates LSP and the principle of contravariance. *Return types*, on the other hand, can be made more restrictive. https://en.wikipedia.org/wiki/Liskov_substitution_principle https://en.wikipedia.org/wiki/Covariance_and_contravariance_(computer_science) ------------------------------------------------------------------------ [2021-03-30 20:31:08] smiley at chillerlan dot net Description: ------------ Hello! I'd like to be able to add parameter type hints for poorly typed interface methods for type security and consistency. We're currently allowed to add return types in case they're not declared in the interface or omit existing type hints in the interface, but for some reason the aforementioned probably most important feature is missing. A userland example would be the dilemma of a PSR-7 update: https://github.com/php-fig/http-message/pull/83 I understand that this might require an RFC, but i don't possess neither the technical insight, nor the mental capacity to start such a process. Don't mind me if plans/feature request for such an update already exist. :) Test script: --------------- <?php // a poorly typed interface interface PoorlyTypedInterface{ public function methodWithoutTypeHints($string, $int); } // currently we're only allowed to add a return type class PoorlyTypedClass implements PoorlyTypedInterface{ public function methodWithoutTypeHints($string, $int):array{ return [$string, $int]; } } // proposal: allow adding parameter type hints class StronglyTypedClass implements PoorlyTypedInterface{ public function methodWithoutTypeHints(string $string, int $int):array{ return [$string, $int]; } } Actual result: -------------- Fatal error: Declaration of StronglyTypedClass::methodWithoutTypeHints(string $string, int $int): array must be compatible with PoorlyTypedInterface::methodWithoutTypeHints($string, $int) ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=80921&edit=1