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Date: Thu, 17 Sep 2015 20:35:58 -0400
Cc: Rowan Collins <rowan.collins@gmail.com>, internals@lists.php.net
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To: Bob Weinand <bobwei9@hotmail.com>
Subject: Re: [PHP-DEV] Let's discuss enums!
From: jbafford@zort.net (John Bafford)


> On Sep 17, 2015, at 20:06, Bob Weinand <bobwei9@hotmail.com> wrote:
>=20
>> Am 18.09.2015 um 01:52 schrieb John Bafford <jbafford@zort.net>:
>>=20
>> If we=E2=80=99re bikeshedding, one feature I would really like to =
see, with typehinting, is warnings if all cases of an enum aren=E2=80=99t =
handled in a switch. So, for example, given our example Weekdays enum, =
if I wrote this code:
>>=20
>> switch(Weekday $someWeekday) {
>> 	case Weekday::MONDAY: break;
>> 	case Weekday::TUESDAY: break;
>> }
>>=20
>> By providing the typehint, I=E2=80=99m indicating that I want to get =
a warning/error that the switch does not cover all enum values. This =
would be very handy if an enum value is added after initial development =
and someone misses a switch statement in cleanup.
>>=20
>> The typehint would also allow generating a warning if someone did =
something like
>>=20
>> switch(Weekday $someWeekday) {
>> 	//case =E2=80=A6 all the weekdays: break;
>> 	case =E2=80=98I am not a Weekday=E2=80=99: echo =E2=80=98Generate =
a fatal error here because string is not a Weekday.=E2=80=99;
>> }
>=20
> So, you mean like an implicit
> default: throw Error("Unhandled enum value Weekday::FRIDAY");
>=20
> Possible, but then you also just can add
> default: assert(0);
> instead of a typehint.
>=20
> At compile-time won't be really possible, as, when the switch is =
encountered, the enum might not yet have been loaded. That's one of the =
consequences of PHP's lazy inclusion system...

Compile-time might not be possible, true, but at least this would =
provide for runtime checks, and the benefit of explicitly stating =
intention is that intention is explicitly stated. Also, it would allow =
the sort of errors I=E2=80=99m proposing be generated to all be =
standardized across all applications, which would allow fancy error =
handlers, such as with Symfony, to offer helpful context-specific =
suggestions. Also, it=E2=80=99d provide static analyzers additional =
information by which to provide correctness alerts.

-John=