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Date: Fri, 25 Mar 2022 12:52:51 -0600
Message-ID: <CAKWdMuj+GnmhCaUp8DJCFt2QMEta9fsZkT-SiMV333Eo3iJt6Q@mail.gmail.com>
To: Guilliam Xavier <guilliam.xavier@gmail.com>
Cc: php internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Typed constants revisited
From: mbniebergall@gmail.com (Mark Niebergall)

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On Fri, Mar 25, 2022 at 10:55 AM Guilliam Xavier <guilliam.xavier@gmail.com>
wrote:

> I intentionally left `abstract` out of `public const bool CAN_FLY;` in the
>> `abstract class` for consistency with the implementation with `interface`,
>> which would also have to be `public const bool CAN_FLY;`. Currently
>> `abstract` is only used in front of methods `abstract function doThing():
>> bool;`. Open to discussion - which way is ideal or preferred? That could be
>> included as a subset of an RFC vote if a consensus during discussion isn't
>> reached.
>>
>
> I understand, but note that methods are implicitly abstract in an
> interface, but it must be explicit in an abstract class; and since I see
> the proposed feature mainly as a "replacement" for abstract static methods
> [whose all implementations just return a literal value]... (anyway, not
> super important)
>

Constants are not abstract in an interface - they must be assigned a value.
Only classes and methods can be abstract. Within an abstract class it is
not valid to have an abstract property. Properties can be defined
`protected int $id;` and optionally assigned a value `protected int $id =
5;`, but cannot be `abstract protected int $id;`. So to me it makes more
sense to have constants follow the same syntax as properties `public const
bool CAN_FLY;` without the `abstract` keyword.

An example:

```
abstract class Bird
{
    public const bool CAN_FLY;
    protected bool $isExtinct;
```

This allows for similar behavior, similar requirements, and similar syntax
- consistency ftw!

There seems to be interest and good use cases (thanks Sara for the good
practical example!). At this point I'm going to work on a new RFC with all
the details and feedback from this discussion.

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