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Date: Fri, 18 Sep 2015 02:48:52 +0200
CC: Rowan Collins <rowan.collins@gmail.com>,
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To: John Bafford <jbafford@zort.net>
Subject: Re: [PHP-DEV] Let's discuss enums!
From: bobwei9@hotmail.com (Bob Weinand)

> Am 18.09.2015 um 02:35 schrieb John Bafford <jbafford@zort.net>:
>=20
>> 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...
>=20
> 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.
>=20
> -John

Static analyzers etc. all can look at the cases and conclude that the =
type indeed should have been of a certain Enum. I don't really see a =
particular advantage here.

And for the run-time checks, just add a default: assert(0); as said. I =
don't see loads of benefits from this extra syntax.
Also, as said, I'd pretty much prefer that to be separated out in a =
different RFC as it isn't crucial to the Enum feature itself.

Bob=