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Date: Wed, 29 Mar 2023 14:01:44 +0300
Message-ID: <CAF-mU4xeyK1XXEir8-xCuuYXOAg7X4NdfOih0u7w9ekuapqMRw@mail.gmail.com>
To: Christian Schneider <cschneid@cschneid.com>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [IDEA] allow extending enum
From: rokas.sleinius@gmail.com (=?UTF-8?Q?Rokas_=C5=A0leinius?=)

Hi!

There's a hypothetical (based on a similar real world problem that I
am facing) example for the use of extending enums in the OP.

And I don't suppose Tim was arguing for not allowing enum
extendability, but rather contributing a real world example where
users who were having some totally legal fun hacking around with
internal PHP code would break said internal PHP code.

Which may or may not be a big deal from my uneducated point of view,
just saying :) And all could be prevented just by adding a `final`
statement to the definition of `IntervalBoundary`.


On Wed, 29 Mar 2023 at 13:42, Christian Schneider <cschneid@cschneid.com> w=
rote:
>
> Am 29.03.2023 um 11:55 schrieb Tim D=C3=BCsterhus <tim@bastelstu.be>:
> > On 3/29/23 11:42, Sebastian Bergmann wrote:
> >> Am 29.03.2023 um 11:31 schrieb Rokas =C5=A0leinius:
> >>> I wouldn't say removing the final attribute from enums actually "brea=
ks" any functionality.
> >> I am with Marco on this: removing the "finality" from enum would be a
> >> major backward compatiblity break as it breaks a fundamental assumptio=
n
> >> about enums.
> >
> > And to give a specific example from PHP 8.3: As part of the Randomizer =
additions RFC (https://wiki.php.net/rfc/randomizer_additions), PHP 8.3 got =
its first "natively included" enum (\Random\IntervalBoundary). This enum wo=
rks together with the new Randomizer::getFloat() method to specify if the g=
iven min and max value may be returned or not.
> >
> > The Randomizer::getFloat() method internally includes switch statement =
that chooses the implementation based on the IntervalBoundary value given.
> >
> > If a user would be able to extend the IntervalBoundary enum, the method=
 would not be able to make sense of it.
> >
> > The IntervalBoundary enum completely enumerates all four possible combi=
nations for the two possible states for each of the two boundaries (2*2 =3D=
 4). By definition there is no other valid value.
>
> I do understand the reason behind making Enums final and your example ill=
ustrates the point very well.
>
> I still have a question I already asked in a different context: If there =
ever is the need to add a case to an Enum, was there any thought put into m=
aking this possible? Or is this categorically ruled out when using Enums?
>
> Let=E2=80=99s look at a very, very hypothetical example: Imagine a Random=
izer is much, much slower for certain boundaries and it is decided that som=
e programs do not care about Closed/Open but instead care more about speed.=
 So they would want to use something like IntervalBoundary::Fastest.
>
> As far as I understand such an addition would *never* be possible, right?=
 This means people defining Enums have to be very very certain that no one =
will ever want another value, right?
>
> Regards,
> - Chris
>
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