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Date: Fri, 24 Jun 2022 18:37:52 +0200
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To: Guilliam Xavier <guilliam.xavier@gmail.com>, Rowan Collins <rowan.collins@gmail.com>
Cc: PHP Internals List <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] [Under Discussion] Auto-implement Stringable for
 string backed enums
From: nicolas.grekas+php@gmail.com (Nicolas Grekas)

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Hi Guilliam,


> > There are also cases where using "->value" is just not possible. I
> mention
> > attributes in the RFC,
>
> which also mentions
> https://wiki.php.net/rfc/fetch_property_in_const_expressions (but with
> "For people that use non-strict mode, this extra =E2=80=9C->value=E2=80=
=9D is
> boilerplate that they'd better remove")
>

Absolutely.

Providing a nice and expressive syntax is critical. We added e.g. short
closures, constructor property promotion, etc. all because we care to not
write ugly code.

With the "Fetch properties of enums in const expressions" RFC, we soon
might be able to reference values in enums with this syntax:
#[MyAttr(MyEnum::Case->value)]

I understand why we're considering this and this might be only me, but I
find this ugly.
The same happens when coding: take_string($enum->value)

This ugliness is part of the problem I'd like to solve. Rowan's proposals
about sets could solve this in a very nice way , but we're not there yet. I
can wait though.



> Symfony YAML has a `!php/const X` feature, which also works when X is
> an Enum::CASE; how about a `!php/enum_value` feature?
>

I submitted something similar today at
https://github.com/symfony/symfony/pull/46771

Otherwise, I also like Rowan's suggestion of implementing "internal
> cast handlers", so that non-strict users could call e.g.
>

I had a look at gmp for example: cast handlers don't work when calling a
function.
They do work when explicit casting and when doing loose comparisons, but
they don't when calling functions (or returning from one.) I don't know the
underlying reason for that behavior but it looks consistent. Unfortunately
that idea looks like a dead end.

In any case, several people requested that it should require to be
> *opted-in* explicitly; but then [for solutions other than "allowing
> user-land to implement Stringable"] we probably also need a way to
> test whether a BackedEnum [instance] is "coercible"?
>

I don't have a solution that meets all the requirements that ppl expressed
so far.
If I could get back in time, I would enable that missing casting rule I
described for gmp in non-strict mode, and I would implement it on backed
enums from the start.

I'm now considering withdrawing the RFC because I don't see a way forward
that could be consensual enough.
If other ppl share my concerns and have a proposal, please let us know.

Nicolas

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