Doc->Bug #81038 [Nab->Opn]: the variance and traits

Edit report at https://bugs.php.net/bug.php?id=81038&edit=1 ID: 81038 Updated by: cmb@php.net Reported by: sh-ya at ya dot ru Summary: the variance and traits -Status: Not a bug +Status: Open -Type: Documentation Problem +Type: Bug -Package: Documentation problem +Package: Scripting Engine problem PHP Version: 7.4.19 -Assigned To: cmb +Assigned To: Block user comment: N Private report: N New Comment: Maybe there is actually a bug, but I don't think it will be fixed. Previous Comments: ------------------------------------------------------------------------ [2021-05-17 12:58:18] sh-ya at ya dot ru comment out "use SomeTrait" and that order will work ------------------------------------------------------------------------ [2021-05-17 10:43:30] cmb@php.net The problem is the order of the definitions. Animal cannot be resolved until AnimalFood is defined, and that trips up the script. This is basically documented[1]: | Unless autoloading is used, the classes must be defined before | they are used. If a class extends another, then the parent class | must be declared before the child class structure. This rule | applies to classes that inherit other classes and interfaces. So yes, the best solution is to use autoloading; alternatively you can fix the order of definitions[2] (that may not always be possible). [1] <https://www.php.net/manual/en/language.oop5.inheritance.php> [2] <https://3v4l.org/RsDcu> ------------------------------------------------------------------------ [2021-05-13 12:55:25] sh-ya at ya dot ru Description: ------------ using the variance requires pre-definition of classes that use traits Test script: --------------- interface Animal { public function eat(AnimalFood $food); } class Dog implements Animal { public function eat(Food $food) {} } trait SomeTrait { public $b = true; } class Food { use SomeTrait; public $i = 0; } class AnimalFood extends Food {} var_dump(new AnimalFood); Expected result: ---------------- object(AnimalFood)#1 (2) { ["i"]=> int(0) ["b"]=> bool(true) } Actual result: -------------- Fatal error: Could not check compatibility between Dog::eat(Food $food) and Animal::eat(AnimalFood $food), because class AnimalFood is not available in ... ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=81038&edit=1