Req #73435 [NEW]: Return type-hinting polymorphism

From: php at haravikk dot me Operating system: PHP version: 7.0.12 Package: PHP Language Specification Bug Type: Feature/Change Request Bug description:Return type-hinting polymorphism Description: ------------ I'd like to propose that when implementing/extending that type-hints for return values can be fulfilled by any sub-class of the same type. In other words, sub-classes, when implementing/extending a method, should be able to provide a stricter type-hint for their return value, so long as it is a sub-class of the parent's type-hint. Please see the test script for an example; in it I would expect to be able to provide a return type-hint of "Bar", as it is a sub-type of "Foo", therefore meeting the original requirements while clarifying that the sub-class is more specific in what specific flavour of "Foo" it will actually return. There is a similar issue (#60107) in which the Liskov Substitution Principle is referenced, however, while allowing this behaviour on method arguments might breach LSP, I believe doing so only for return types should be okay. Test script: --------------- class Foo {} class Bar extends Foo {} abstract class MyType { abstract function example(): Foo; } class MyTypeImpl extends MyType { function example(): Bar { /* Do something here */ } } Expected result: ---------------- The implementation of the example method by "MyTypeImpl" should be accepted as a valid implementation of the method in "MyType". Actual result: -------------- Fatal error: Declaration of MyTypeImpl::example(Bar $value) must be compatible with MyType::example(Foo $value) in test.php on line 12 -- Edit bug report at https://bugs.php.net/bug.php?id=73435&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=73435&r=trysnapshot54 Try a snapshot (PHP 5.5): https://bugs.php.net/fix.php?id=73435&r=trysnapshot55 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=73435&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=73435&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=73435&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=73435&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=73435&r=needscript Try newer version: https://bugs.php.net/fix.php?id=73435&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=73435&r=support Expected behavior: https://bugs.php.net/fix.php?id=73435&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=73435&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=73435&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=73435&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=73435&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=73435&r=dst IIS Stability: https://bugs.php.net/fix.php?id=73435&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=73435&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=73435&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=73435&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=73435&r=mysqlcfg