Online PHP editor | output for l8eG6

<?php interface I {} interface J {} // Simulate a "never" parameter type. interface AlmostNever extends I, J {} class C implements I {} interface Base { public function foo(AlmostNever $x, AlmostNever $y): mixed; } interface ReturnI extends Base { public function foo(AlmostNever $x, AlmostNever $y): I; } interface AcceptI extends Base { public function foo(I $x, AlmostNever $y): mixed; } interface AcceptSecondI extends Base { public function foo(AlmostNever $x, I $y): mixed; } class AcceptReturnI implements ReturnI, AcceptI, AcceptSecondI { public function foo(I $x, I $y): I { return $x; } } function f(AcceptI&AcceptSecondI&ReturnI $callme, I $x): I { return $callme->foo($x, $x); } f(new AcceptReturnI(), new C(), new C());