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Date: Wed, 30 Mar 2022 15:50:29 +0200
Message-ID: <CAC5V6ggybWQ6pntF5B+4pvbOaiMCKpM=dxhcc4TZk=jjufKb4Q@mail.gmail.com>
To: Mark Niebergall <mbniebergall@gmail.com>
Cc: php internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000b826c905db6fd473"
Subject: Re: [PHP-DEV] Typed constants revisited
From: guilliam.xavier@gmail.com (Guilliam Xavier)

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Hi Mark,

I have updated the RFC https://wiki.php.net/rfc/typed_class_constants with
>>> more details and examples from this thread, and updated the RFC status to
>>> Under Discussion. Hopefully the updated RFC helps answer questions and
>>> clarifies what the proposal includes.
>>>
>>
Thanks (I assume that you talked with the original author) -- not sure if
you should have started a new thread with the "[RFC]" tag in the subject?


> I think you should also update the "Supported types" section.
>> Starting with enums, constants can also be objects. Once a good technical
>> solution is found, any object would be supported probably
>> https://wiki.php.net/rfc/new_in_initializers#future_scope
>> I think that only void, never and callable types should not be supported,
>> just like on properties.
>>
>
> I have updated the "Supported types" to list out all types that are
> supported and which types are not supported.
>

A few comments, by subsection:

  - **Supported types**: This corresponds to the types currently allowed
for const values (as well as unions thereof) except it [still] doesn't
mention enums (which internally are classes implementing the `UnitEnum`
interface, and whose values are ultimately of `object` type) although
currently allowed. It also doesn't mention `mixed` (used later in examples).
  - **Strict and coercive typing modes**: I didn't understand it on first
read; I had to read the later "Constant values" section and compare both
with
https://wiki.php.net/rfc/typed_properties_v2#strict_and_coercive_typing_modes
and https://wiki.php.net/rfc/typed_properties_v2#default_values
  - **Inheritance and variance**: Several occurrences of "Class constants"
should probably be "*Typed* class constants". Also, I still think that
`protected bool $isExtinct` is *not* a good parallel to `public const bool
CAN_FLY` (see my previous message).
  - **Constant values**: You should probably remove the `iterable` example
now [and maybe add an `enum` one].


> Constants cannot be objects since objects are mutable, so typed constants
> will not be allowed to be an enum (which is technically an object). A typed
> constant _may_ be an enum value though, so the following example will be
> valid:
>
> ```
> enum Fruit
> {
>     case Apple;
>     case Banana;
> }
>
> class Colors
> {
>     protected const string RED = Fruit::Apple;
>     protected const string YELLOW = Fruit::Banana;
> }
> ```
>

This is incorrect, `Fruit::Apple` is of type `Fruit` (ultimately `object`),
not `string`. But it is *not* mutable, and *is* allowed as a const value
currently.

Besides, I realized that the RFC is [only] for *class* constants; what
about *namespaced (and global)* constants?

Regards,

-- 
Guilliam Xavier

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