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 enums cannot: typing existing scalar APIs without breaking callers, ad-hoc open value sets that can grow without BC breaks, and direct scalar interop (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 types (e.g., `int -1..1`) as a future extension, and the author clarifies that literal types shine most for typed structured payloads like decoded JSON responses where data is genuinely scalar on the wire.
