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Date: Thu, 29 Jul 2021 18:23:36 -0500
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Subject: Re: [PHP-DEV] PHP 8.1 enum const expressions problem
From: larry@garfieldtech.com ("Larry Garfield")

On Thu, Jul 29, 2021, at 5:16 PM, =D0=9A=D0=B8=D1=80=D0=B8=D0=BB=D0=BB =D0=
=9D=D0=B5=D1=81=D0=BC=D0=B5=D1=8F=D0=BD=D0=BE=D0=B2 wrote:
>=20
> Hello internals! I apologize if such a discussion has already taken=20=

> place, but I didn't find anything like it.
> =C2=A0
> When working with enums, I ran into problems that are currently not=20=

> resolved.=C2=A0In some cases, enumerations require self references and=
=20
> constant arithmetic expressions:
> =C2=A0
> enum Example: int
> {
> =C2=A0 =C2=A0 case A=C2=A0=3D 0b0001;
> =C2=A0 =C2=A0 case B=C2=A0=3D 0b0010;
> =C2=A0 =C2=A0 case C=C2=A0=3D 0b0100;
> =C2=A0
> =C2=A0 =C2=A0 public const EXAMPLE_MASK=C2=A0=3D self::A | self::B; //=
 <<=C2=A0Invalid expression
> =C2=A0 =C2=A0 public const EXAMPLE_MASK2 =3D self::A->value | self::B-=
>value; // <<=C2=A0Same
> }
> =C2=A0
> Similar examples can be taken in the existing PHP=C2=A0code, for examp=
le,=20
> for attributes (Attribute::TARGET_ALL)=C2=A0which is a binary mask for=
=20
> existing =C2=ABtargets=C2=BB.=C2=A0Thus, if targets=C2=A0for attribute=
s were implemented=20
> through enumerations, and not through constants, then it would be=20
> impossible to implement such functionality.
> =C2=A0
> In addition, enumeration values are not part of constant expressions,=20=

> so implementation through "Example::A->value" is also not available.
> =C2=A0
> Can you please tell me, maybe there have already been some discussions=
=20
> of this problem?=C2=A0And if not, then maybe we should solve this prob=
lem=20
> before PHP=C2=A08.1 release?=C2=A0Since it seems to me that the lack o=
f such=20
> functionality is quite critical.

What you're describing is enum sets.  That is, a value that is itself a =
union of two enum values.  Those are not supported at this time.  It's a=
ctually a bit tricky to do, since internally enum cases are not a bit va=
lue but an actual full PHP object.  So self::A | self::B would be trying=
 to bitwise-OR two objects, which is of course meaningless.

The second doesn't work because technically self::A is an object, not a =
constant, so it cannot be used in a constant expression.  The only dynam=
icness added in 8.1 was for "new" expressions in initializers.  The obje=
cts don't exist at compile time so they cannot be reduced down to a cons=
tant value pre-runtime.

I agree the current situation is suboptimal.  I don't think anyone is op=
posed to enum sets, but they're a non-trivial amount of work to do and w=
e haven't figured out how to do them yet.  There's no simple way to addr=
ess it as as bug, so any larger effort will have to wait for 8.2.

--Larry Garfield