Newsgroups: php.internals
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Date: Wed, 03 Sep 2025 23:23:38 +0200
To: internals@lists.php.net
Subject: Re: [PHP-DEV] enum flag backed enum
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References: <9c875e83-ddc8-4c5c-a368-747bef46e4a2@app.fastmail.com>
Message-ID: <F60093E2-9310-4E6D-B1CA-C4B98D60B097@mabe.berlin>
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From: marc@mabe.berlin ("Marc B.")

Hi Rob,

Am 3=2E September 2025 22:44:58 MESZ schrieb Rob Landers <rob@bottled=2Eco=
des>:
>Hello internals,
>
>I would like to propose a new type of backed enum: flag=2E This is an int=
eger-backed enum that requires power-of-two values that can be combined wit=
h the bitwise operators to be used as flags=2E
>
>In some core functions, it might look like this:
>
>enum JSON_FLAG: flag {
>  case None =3D 0;
>  case ThrowOnError =3D 0x1 << 1;
>  // etc=2E
>  case PrettyPrint =3D 0x01 << 4;
>  // etc=2E
>}
>
>function json_decode(string $data, bool $assoc =3D false, int $depth =3D =
512, JSON_FLAG|int $options =3D JSON_FLAG::None) {}
>
>json_decode($data, options: JSON_FLAG::ThrowOnError | JSON_FLAG::PrettyPr=
int);
>
>Note that the goal here isn=E2=80=99t so much to save typing space, as it=
 is to provide easier discoverability through IDEs, better type safety, and=
 better ergonomics in the language overall=2E
>
>Attempting to use a backed value that is not a power-of-two would result =
in a compilation error=2E Bitwise operations are performed as though they=
=E2=80=99re performed on a regular integer=2E
>
>What do you think?

I think what we actually would need is an EnumSet which can be used with a=
ny enum but (based on its ordinal) but this would play nicely together with=
 generics `new EnumSet<JsonOption>`=2E

>
>I couldn=E2=80=99t find any similar proposals (listed on the RFC page) be=
fore proposing this on the list, so if you=E2=80=99re working on this, plea=
se speak up; I=E2=80=99d like to join forces=2E
>
>=E2=80=94 Rob

Marc