On Mon, 15 Jun 2026 at 03:03, David Gebler <[email protected]> wrote:
>
> On Mon, Jun 15, 2026 at 2:24 AM Seifeddine Gmati <[email protected]>
> wrote:
>>
>> Hello Internals,
>>
>> I'd like to start the discussion on a new RFC adding literal scalar
>> types to PHP.
>
>
> Prima facie, I feel like enums already do what this aims to achieve, much
> better.
>
>>
>>
>> - RFC: https://wiki.php.net/rfc/literal_scalar_types
>> - Implementation: https://github.com/php/php-src/pull/22314
>>
>> Thanks,
>> Seifeddine.
Hi David,
I agree enums are the better fit for a lot of cases. but not all.
1. describing APIs that already exist. `array_filter`'s `$mode` really
accepts `0|1|2`, but it's typed `int` because that's all the type
system can say today. we can't retype it as an enum without breaking
every caller. a literal union lets the signature state the actual
contract.
2. ad-hoc / open value sets. for a library, "ascii"|"utf-8" would need
its own named symbol ( `enum BorderStyle { case Ascii; case Utf8 }`, a
new file, an import ) for what is really two strings. and because an
enum is a closed set, adding a third style later breaks any consumer
that match-es over it without a default. widening the union on a
parameter ( "ascii"|"utf-8"|"unicode" ) is contravariant, so it breaks
nobody.
3. scalar interop. a literal value is the scalar, so it works as an
array key, compares with ===, round-trips through json, etc. enum
cases are objects and don't.
so they overlap a lot, but literal unions reach things enums
structurally can't: existing scalar APIs, and open sets that grow
without a BC break.
Cheers,
Seifeddine.
