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run code in 300+ PHP versions simultaneously
<?php interface OldInterface { public function foo(); } interface NewInterface { public function foo(): mixed; } final class MyClass implements OldInterface, NewInterface { public function foo() { return null; } } $c = new MyClass(); $c->foo();
Output for 7.4.0 - 7.4.33, 8.0.1 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
Fatal error: Declaration of MyClass::foo() must be compatible with NewInterface::foo(): mixed in /in/EntQu on line 13
Process exited with code 255.

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