Re: [RFC] [Discussion] Literal Scalar Types

On Mon, 15 Jun 2026 at 19:25, Lars Nielsen <lars@lfweb.dk> wrote: > > > Den 15. jun. 2026 kl. 19.23 skrev Sarina Corrigan <sarina.corrigan@gmail.com>: > >  > It may be worth mentioning that within the Pattern Matching RFC future scope, and mentioned a > couple times within the discussion thread for the RFC, there is a similar proposal that would allow > for this without using specific literal types. > > It's outlined in > https://github.com/Crell/php-rfcs/blob/master/pattern-matching/future.md > under "Parameter or return guards" > > It would allow for: > > ``` > function setLogLevel (string $level is 'debug' | 'info' | > 'warning' | 'error'): void {} > ``` > > Of course, I don't think that a potential future scope of an in-draft RFC is reason to > dismiss a more direct implementation of literal scalar types, but it may be useful to compare other > ways we could achieve the same functionality. I personally find pattern matching within > parameter/return types more versatile while keeping direct typing system more simplified. > Specifically for a range feature that Ben Ramsey brought up, pattern matching for parameters seems > much more appropriate. > > All that being said, I would gladly welcome literal scalar types. > > On Sun, Jun 14, 2026, 21:24 Seifeddine Gmati <azjezz@carthage.software> wrote: >> >> Hello Internals, >> >> I'd like to start the discussion on a new RFC adding literal scalar >> types to PHP. >> >> - RFC: https://wiki.php.net/rfc/literal_scalar_types >> - Implementation: https://github.com/php/php-src/pull/22314 >> >> Thanks, >> Seifeddine. > > > Hi, > This sounds very promising. But I would be confused about receiving a TypeError when just the > value of the parameter is wrong. > > As described in the RFC if I send 4 to a parameter that could only be 1, 2 or 3. I would expect > a TypeError if I sent “abc” ? > > Kind regards > Lars Nielsen Hi Lars, I think the confusion comes from treating "type" and "value" as two separate things, which is the usual mental model. Literal scalar types deliberately blur that line: each value is itself a type, a unit type containing exactly one value. So 1|2|3 is not "an int that happens to be restricted", it is the union of three unit types 1, 2 and 3. Under that view, both 4 and "abc" fail for the same reason: neither is a member of the declared type. There is no separate "the value is wrong" category, it is all type membership, so a TypeError is the consistent outcome. It is the same thing that already happens with the true type today: passing false to a true parameter is a TypeError, even though both are booleans.