Iron is a lightweight library for refined types in Scala 3.
It enables attaching constraints/assertions to types, to enforce properties and forbid invalid values.
- Catch bugs. In the spirit of static typing, use more specific types to avoid invalid values.
- Compile-time and runtime. Evaluate constraints at compile time, or explicitly check them at runtime (e.g. for a form).
- Seamless. Iron types are subtypes of their unrefined versions, meaning you can easily add or remove them.
- No black magic. Use Scala 3's powerful inline, types and restricted macros for consistent behaviour and rules. No unexpected behaviour.
- Extendable. Easily create your own constraints or integrations using classic typeclasses.
To learn more about Iron, see the microsite.
import io.github.iltotore.iron.*
import io.github.iltotore.iron.constraint.numeric.*
def log(x: Double :| Positive): Double =
Math.log(x) //Used like a normal `Double`
log(1.0) //Automatically verified at compile time.
log(-1.0) //Compile-time error: Should be strictly positive
val runtimeValue: Double = ???
log(runtimeValue.refineUnsafe) //Explicitly refine your external values at runtime.
runtimeValue.refineEither.map(log) //Use monadic style for functional validation
runtimeValue.refineEither[Positive].map(log) //More explicitlyIron provides useful errors when a constraint does not pass:
log(-1.0)-- Constraint Error --------------------------------------------------------
Could not satisfy a constraint for type scala.Double.
Value: -1.0
Message: Should be strictly positive
----------------------------------------------------------------------------Or when it cannot be verified:
val runtimeValue: Double = ???
log(runtimeValue)-- Constraint Error --------------------------------------------------------
Cannot refine non full inlined input at compile-time.
To test a constraint at runtime, use the `refine` extension method.
Note: Due to a Scala limitation, already-refined types cannot be tested at compile-time (unless proven by an `Implication`).
Inlined input: runtimeValue
----------------------------------------------------------------------------SBT:
libraryDependencies += "io.github.iltotore" %% "iron" % "version"Mill:
ivy"io.github.iltotore::iron:version"Note: replace version with the version of Iron.
| Module | JVM | JS | Native |
|---|---|---|---|
| iron | ✔️ | ✔️ | ✔️ |
| iron-borer | ✔️ | ✔️ | ❌ |
| iron-cats | ✔️ | ✔️ | ✔️ |
| iron-circe | ✔️ | ✔️ | ✔️ |
| iron-ciris | ✔️ | ✔️ | ✔️ |
| iron-decline | ✔️ | ✔️ | ✔️ |
| iron-doobie | ✔️ | ❌ | ❌ |
| iron-jsoniter | ✔️ | ✔️ | ✔️ |
| iron-scalacheck | ✔️ | ✔️ | ❌ |
| iron-skunk | ✔️ | ✔️ | ✔️ |
| iron-upickle | ✔️ | ✔️ | ✔️ |
| iron-zio | ✔️ | ✔️ | ❌ |
| iron-zio-json | ✔️ | ✔️ | ❌ |
Here is a non-exhaustive list of projects using Iron.
Submit a PR to add your project or company to the list.