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Date: Fri, 30 Jul 2021 21:01:57 +0100
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Subject: Re: Fwd: Re[2]: [PHP-DEV] PHP 8.1 enum const expressions problem
From: rowan.collins@gmail.com (Rowan Tommins)

On 30/07/2021 18:24, Kirill Nesmeyanov wrote:
> enum ErrorGroup: int
> {
>      case NOTICE = 0;
>      case WARNING = 10;
>      case ERROR = 20;
> }
>   
> enum ErrorCode: int
> {
>      case UNKNOWN = 0;
>      
>      case A = ErrorGroup::NOTICE + 1;
>      case B = ErrorGroup::NOTICE + 2;
>      case С = ErrorGroup::NOTICE + 3;
>      case D = ErrorGroup::WARNING + 1;
>      case E = ErrorGroup::ERROR + 1;
> }


As I say, those are not enums in the way the current feature defines "enum".

An enum, as implemented in the current 8.1 alphas, is not just a special 
kind of constant, even if it has an integer or string associated. Every 
enum is its own type (essentially a class), and every value is a 
distinct value of that type (essentially an instance), which compares 
equal only to itself.

var_dump(ErrorGroup::WARNING); // enum(ErrorGroup::WARNING);
var_dump(ErrorGroup::WARNING == 10); // bool(false)
var_dump(get_class(ErrorGroup::WARNING)); // string(10) "ErrorGroup"


There are languages where enums are just fancy names for integers, and 
you can write things like "if ( ErrorCode::D >= ErrorGroup::WARNING )". 
In my opinion, that makes enums much less useful, because it means you 
can also write nonsensical things like "if ( Month::JANUARY <= 
Day::WEDNESDAY )".

If you want to pass around an integer, but have a convenient name for 
it, you can still use a class constant. The main value of native enums, 
in my opinion, is being able to write strongly typed code saying "this 
accepts a value of type ErrorGroup, and nothing else".

Regards,

-- 
Rowan Tommins
[IMSoP]