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Date: Mon, 18 Feb 2019 16:12:47 +0100
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To: Rowan Collins <rowan.collins@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV][RFC] Allow void return type variance
From: mike.php.net@gmail.com (Michael Wallner)

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I second Rowans thoughts.

Am So., 17. Feb. 2019, 17:36 hat Rowan Collins <rowan.collins@gmail.com>
geschrieben:

> On 04/02/2019 03:22, Wes wrote:
> > Recent events convinced me to write this RFC :P
> >
> > Please have a read here https://wiki.php.net/rfc/allow-void-variance
>
>
> I was thinking about this this afternoon, and I think the current
> behaviour is actually correct, and this constraint should stay invariant.
>
> My reasoning is that ": void" isn't actually a *type constraint* - there
> is no "void type" to apply the rules of covariance and contravariance
> to. It's tempting to place it on a par with ": null", but a void
> function evaluates to null only for the same reason an unset variable
> does: because the runtime has to give you *something*.
>
> Instead, ": void" in PHP represents a *behavioural constraint* on the
> function - it declares that within this function, anything of the form
> "return $value" is to be treated as an error. In other languages, the
> same constraint might be enforced by declaring the routine as a
> "procedure" rather than a "function".
>
> As such, it is more appropriate to compare "void vs non-void" to "static
> vs non-static", which is an invariant constraint - you can't over-ride a
> static method with a non-static one, or vice versa.
>
>
> (Incidentally, the RFC mentions TypeScript as precedent; there, "void"
> apparently *is* a type, not just a keyword in function signatures:
> https://www.typescriptlang.org/docs/handbook/basic-types.html)
>
> Regards,
>
> --
> Rowan Collins
> [IMSoP]
>
>
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