A friendly newtype library for Scala 3.
"io.github.kitlangton" %% "neotype" % "0.2.4"- Compile-time Checked Values
- Write validations as plain, old Scala expressions
- Helpful compilation errors (see below)
- No runtime allocations (Thanks to
inlineandopaque type) - Integrates with other libraries (e.g.
zio-json,circe,tapir, etc.)
Here is how to define a compile-time validated Newtype.
import neotype.*
// 1. Define a newtype.
object NonEmptyString extends Newtype[String]:
// 2. Optionally, define a validate method.
override inline def validate(input: String): Boolean =
input.nonEmpty
// 3. Construct values.
NonEmptyString("Hello") // OK
NonEmptyString("") // Compile ErrorAttempting to call NonEmptyString("") would result in the following compilation error:
Error: /src/main/scala/examples/Main.scala:9:16
NonEmptyString("")
^^^^^^^^^^^^^^^^^^
—— Newtype Error ——————————————————————————————————————————————————————————
NonEmptyString was called with an INVALID String.
input: ""
check: input.nonEmpty
———————————————————————————————————————————————————————————————————————————Neotype integrates with the following libraries.
- zio-test
DeriveGen - zio-json
- zio-config
- zio-schema
- play-json
- tapir
- quill
- circe
- jsoniter
import neotype.*
import neotype.ziojson.given
import zio.json.*
type NonEmptyString = NonEmptyString.Type
object NonEmptyString extends Newtype[String]:
override inline def validate(value: String): Result =
if value.nonEmpty then true else "String must not be empty"
case class Person(name: NonEmptyString, age: Int) derives JsonCodec
val parsed = """{"name": "Kit", "age": 30}""".fromJson[Person]
// Right(Person(NonEmptyString("Kit"), 30))
val failed = """{"name": "", "age": 30}""".fromJson[Person]
// Left(".name(String must not be empty)")By importing neotype.ziojson.given, we automatically generate a JsonCodec for NonEmptyString. Custom
failure messages are also supported (by overriding def failureMessage in the Newtype definition).