PHP RFC: Allow abstract function override

• Version: 0.1
• Date: 2017-03-01
• Author: @WesNetmo @ Twitter
• Status: Implemented (in PHP 7.2)
• First Published at: https://wiki.php.net/rfc/allow-abstract-function-override

PHP 7 introduced type declarations for return and improved ones for parameters. They currently support a very limited kind of variance (only to no-type):

<?php class A { function bar(stdClass $x){} } class B extends A { function bar($x): stdClass{} }

However, this isn't currently matched by the equivalent abstract declarations:

<?php abstract class A { abstract function bar(stdClass $x); } abstract class B extends A { abstract function bar($x): stdClass; } class C extends B { function bar($x): stdClass{} } // Fatal error: Can't inherit abstract function A::bar() // (previously declared abstract in B)

This RFC proposes to allow this, even if it has very few uses, and because there is no reason to disallow a compatible redefinition.

Additionally, it comes in handy for documentation:

interface A{ function doSomething(); }   interface B extends A{ function doSomethingElse(); }   abstract class AProxy implements A{ abstract protected function getOrigin(): A; function doSomething(){ return $this->getOrigin()->doSomething(); } }   // This phpdoc syntax has quirks in phpdocumentor // apigen and phpstorm, and it's almost unmanageable // as phpdoc interpreters have poor multiline support // (imagine documenting all the parameters, the return // type, all the throws...): /** @method B getOrigin() */ abstract class BProxy extends AProxy implements B{ /** @return B */ // This is much better! abstract protected function getOrigin(): A; function doSomethingElse(){ return $this->getOrigin()->doSomethingElse(); } }

And, obviously, it will gain more uses when PHP will support a full-featured type variance.

None.

7.2

2/3 majority required.

Pull request to handle the change: https://github.com/php/php-src/pull/2531

Discussion on externals.io