fthomas/refined

Health v2 · maintenance only

Adoption not part of the score

1733 stars · 153 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

refined is a Scala library for refinement types, letting you attach type-level predicates to base types so value constraints are checked at compile time (for literals) or runtime (for arbitrary values). It is a port of the Haskell refined library and includes inference rules for converting between compatible refined types.

Use cases

• enforce that an Int is positive at compile time
• validate runtime values against predicates and get Either results
• constrain string values like non-empty or matching a regex via types
• convert between refined types when predicates imply each other
• catch invalid domain values as compile errors instead of runtime bugs

When to choose

• you write Scala and want value constraints encoded in types
• you want compile-time validation of literals and safe conversions between constrained types
• you prefer typelevel-style functional programming idioms

When to avoid

• you work outside the Scala/JVM ecosystem
• your team finds type-level predicates too complex for the codebase
• you need validation in dynamically typed languages

Facets

library · maturity active

type-system form-handling programming-languages developer-tools jvm refinement-types typelevel scala compile-time-validation type-safety

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