A PHP internals mailing list discussion around a proposed RFC to add literal scalar types to PHP, allowing function signatures to express exact allowed values like `0|1|2` or `'success'|'error'`. The RFC author argues these fill gaps that enums cannot: describing existing scalar APIs without breaking callers, ad-hoc open value sets that can grow without BC breaks, and direct scalar interoperability (JSON round-trips, array keys, === comparisons with raw values). Skeptics counter that enums already handle most cases, backed enums cover scalar interop, and a gradual enum migration path exists for legacy APIs. The discussion also touches on potential range syntax (e.g., `int -1..1`) and the strongest use case identified is typing structured scalar payloads like decoded JSON responses.
