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Date: Thu, 17 Sep 2015 20:49:35 -0400
Cc: Rowan Collins <rowan.collins@gmail.com>,
        PHP internals <internals@lists.php.net>
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References: <55FB4791.4040807@gmail.com> <CAOsHV+tE_JCd05K8iTgRoEi40n_ryOJ0E0fqCESae9Vep9F=vw@mail.gmail.com> <55FB533F.7080301@gmail.com> <BLU436-SMTP36B564DE5BD199CFB724DFE2590@phx.gbl>
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 20:15, Bob Weinand <bobwei9@hotmail.com> wrote:
>=20
>> Am 18.09.2015 um 01:56 schrieb Rowan Collins =
<rowan.collins@gmail.com>:
>>=20
>> On 18/09/2015 00:16, Marcio Almada wrote:
>>> A kitten is working on thathttps://wiki.php.net/rfc/enum. Many =
points
>>> on the linked RFC are compatible to the points you raised so it =
might
>>> be worth reading before even starting any new proposal.
>>=20
>> Aha, I hadn't seen that, should have thought to search the wiki. =
Still, interesting that we seems to mostly agree on the key decisions, =
although I've gone into more detail about things that he's left as =
Future Scope, which is fair enough.
>>=20
>> The main thing I'd change if I was writing it is the implicit =
"ordinal" property; I don't really see the point of insisting that the =
order I write "Red, Green, Blue" has some meaning. On the other hand, =
I'd give much more prominence to the name, e.g. by making values() =
return an associative array. You're much more likely to want to say "the =
value whose name is 'RED'" than "the value I defined first in the list", =
IMHO.
>>=20
>> If you have some kind of initialiser syntax for the values - with or =
without a constructor - you get to have ordinals or explicit values =
(like the Flags example) if you want them, and just names if not:
>>=20
>> enum RenewalAction{
>>   Deny( 0 ),
>>   Approve( 1 );
>>=20
>>   public $ordinal;
>> }
>> enum Flags{
>>   a (1  <<  0),
>>   b( 1  <<  1),
>>   c(  1  <<  2),
>>   d(  1  <<  3 ); public $value; }
>>=20
>> enum PimaryColours { RED, GREEN, BLUE }
>>=20
>> Regards,
>>=20
>> --=20
>> Rowan Collins
>> [IMSoP]
>=20
> The reason it is not an associative array is that the names are not =
important.
>=20
> But we actually need ordinal(), else we'll end up writing =
array_search(TheEnum::values(), $value).
> It's mainly important for the purpose of serializing/unserializing =
(manually or internally).
>=20
> You never should *rely* on the ordinal value of the enum for anything. =
Enums are supposed to be value-less. It's a type. It's not a value. The =
only usage of the value is going external.
>=20
> Also, I honestly think the Flags example is a bad one. (At least as =
long as we don't have a possibility to typehint combined enums...). If =
you need that, use class constants. They provide exactly what you need.
>=20
> Bob

Besides providing serialization mapping (or, the equivalent of a =
__toString() value if the enum is used in a strong context), an =
important benefit to providing a value for enums would be to allow for =
changing or deprecating enums. So you might want to say something like:

enum FormEvents {
	PRE_SUBMIT,
	PRE_BIND =3D PRE_SUBMIT, //deprecated name, provide mapping to =
new name
}

Another good reason for wanting to provide values is so that you could =
write code like this:

$eventHandlers =3D [
	FormEvents::PRE_SUBMIT =3D> function() { =E2=80=A6 },
	FormEvents::POST_SUBMIT =3D> function() { =E2=80=A6 },
	...
];

Although maybe the ideal solution here would be to allow for array =
indexes to have more types than just int and string (so that the array =
index actually is the enum, not some serialized representation).

-John=