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Date: Fri, 30 Jul 2021 12:45:45 +0200
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Subject: Re: Fwd: Re[2]: [PHP-DEV] PHP 8.1 enum const expressions problem
From: marc@mabe.berlin (Marc Bennewitz)


On 30.07.21 02:01, Кирилл Несмеянов wrote:
> Yes, I saw this short description in your RFC ( https://wiki.php.net/rfc/enumerations ) about «enum sets». However, I do not quite understand why we can not now add a cast to scalars (string and int) and math expressions, which would solve this problem? This behavior has  already been implemented for GMP objects.
>
> $mask = gmp_init(0b0001) | gmp_init(0b0010); // object(GMP) { num = 3; }
> echo $mask; // 3
>   
> $mask = $mask + 1; // object(GMP) { num = 4; }
> $mask instanceof \GMP; // true
>   
> I mean, for such cases, we can create a new "virtual enum case" containing a new value instead special «EnumSetCase».
>   
> enum Some: int
> {
>      case A = 0b0001;
>      case B = 0b0010;
> }
>   
> var_dump(Some::A | Some::B); // enum(Some::@anonymous) { value = 3; }
>   
> I don’t think that it is necessary to consider the «enum sets» as a separate case, cause addition is also a fairly popular case:
>   
> case LAST = self::B + 1;
>   
> Like any other mathematical operations.

I think you missing something

Consider this example:

enum Some: int
{
     case A = 0b0001;
     case B = 0b0010;
     case C = 0b0011;
}

var_dump(Some::B | Some::C)

This should result in a set of B|C but with your logic it's the same as 
just C.

and it also needs to work with strings:

enum Some: string
{
     case A = 'a';
     case B = 'b';
     case C = 'c';
}

This is where enum sets comes into play.

Without having PHP internals C knowledge I think it should be possible 
to introduce an EnumSet which internally handles a bit array where each 
bit is pointing to the position (ordinal) of an enum case but I don't 
think the ordinal position is guarantied to be stable over 
processes/versions so this would not directly by serializable nor do we 
have generics to define an enum set of a specific type (ala EnumSet<Some>).

Marc