Re: [RFC] Transform void into an alias for null

On 02/06/2025 17:27, Gina P. Banyard wrote:

The objective is to fix a weird quirk of PHP's type system, where void lives in its own type hierarchy. This is visible mainly in that a lack of return type is not isomorphic to a function that has a return type of mixed.

I think if "void" was added now, it would be an attribute, rather than a type. It is in effect the exact opposite of #[\NoDiscard], and distinguishes between these two cases: interface Foo {    public function getSomething(): ?Something; } class MyFoo implements Foo {    public function getSomething(): null {

       // My result is always null, but still meaningful to consumers of the Foo interface
       return null;

   }    #[\DiscardReturn]    public function doSomething(): null {

        // I have no meaningful information to return; any assignment of my implicit value is a mistake

   } } I agree the type hierarchy you describe is weird, but rather than throwing away the functionality completely, I wonder if we can make it more consistent: - Make "no return type declared" and "mixed" equivalent - Make "void" a sub-type of "null", and therefore a sub-type of "mixed" If I've got that right, this would then be legal: class A{ public function foo() {} } class B extends A{ public function foo(): mixed{} } class C extends B{ public function foo(): null{} } class D extends C{ public function foo(): void{} } class E extends D{ public function foo(): never {} } That seems reasonable enough; I may have missed something important, though. Regards, -- Rowan Tommins [IMSoP]