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 that enums cannot: describing 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 non-exhaustive enum marker RFC could address open sets. The author concedes enums are better for named, reusable, behaviour-carrying sets, but maintains literal types are uniquely suited for typed scalar data on the wire, especially in future array shape typing scenarios.
