Req #78325 [Nab]: Function overloading type prevents overloading

Edit report at https://bugs.php.net/bug.php?id=78325&edit=1 ID: 78325 Updated by: nikic@php.net Reported by: dallas at ekkysoftware dot com Summary: Function overloading type prevents overloading Status: Not a bug Type: Feature/Change Request Package: Class/Object related Operating System: Both PHP Version: 7.1.30 Assigned To: cmb Block user comment: N Private report: N New Comment: The return type change is allowed in PHP 7.4 (the parameter type change is not, as it is unsound). Previous Comments: ------------------------------------------------------------------------ [2019-07-23 08:31:10] cmb@php.net Sorry, but your problem does not imply a bug in PHP itself. For a list of more appropriate places to ask for help using PHP, please visit http://www.php.net/support.php as this bug system is not the appropriate forum for asking support questions. Due to the volume of reports we can not explain in detail here why your report is not a bug. The support channels will be able to provide an explanation for you. Thank you for your interest in PHP. You're trying to use covariant method signatures here, which violates the Liskov Substitution Principle, and is therefore not allowed in PHP. ------------------------------------------------------------------------ [2019-07-23 08:26:55] dallas at ekkysoftware dot com Description: ------------ Issues with overriding parameters of the same function with different types is causing a compilation errors that I don't know how to fix. If there is a fix, can you please let me know and put it somewhere on the Internet so Google and I can find it. Test script: --------------- class Fie{ protected $value; function copy(Fie $new) : Fie { $this->value = $new->value; return $this; } } class Foh extends Fie{ protected $field; function copy(Foh $new) : Foh { $this->field = $new->field; return parent::copy($new); } } Expected result: ---------------- Not needing to totally rewrite Fie's code in Foh. $n = new Foh(); $b = new Foh(); $b->copy($n); Actual result: -------------- PHP Fatal error: Declaration of Foh::copy(Foh $new): Foh must be compatible with Fie::copy(Fie $new): Fie in test_file.php on line 29 Fatal error: Declaration of Foh::copy(Foh $new): Foh must be compatible with Fie ::copy(Fie $new): Fie in test_file.php on line 29 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=78325&edit=1