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 literal types fill gaps 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 non-exhaustive enum marker RFC could address open sets. The author concedes enums are better for named reusable sets but maintains literal types are uniquely suited for typed raw scalar data like decoded JSON payloads and discriminated unions on the wire.
