Grogs/neotype

A friendly newtype library for Scala 3

neotype

A friendly newtype library for Scala 3.

"io.github.kitlangton" %% "neotype" % "0.1.0"

Features

• Compile-time Checked Values
• Write validations as plain, old Scala expressions
• Very Helpful Error Messages (see below)
• No Runtime Allocations (Thanks to inline and opaque type)
• Ability to integrate with other libraries (e.g. zio-json, circe, etc.)

Example

import neotype.*

// Define a newtype:
given NonEmptyString: Newtype[String] with
  // Hey, a plain old Scala expression!
  inline def validate(input: String): Boolean =
    input.nonEmpty

// Wrap values, which checked at compile-time:
NonEmptyString("Hello") // OK
NonEmptyString("")      // Compile Error

Error: /Users/kit/code/neotype/examples/src/main/scala/neotype/examples/Main.scala:9:16 
  NonEmptyString("")                  
  ^^^^^^^^^^^^^^^^^^
  —— Newtype Error ——————————————————————————————————————————————————————————
  NonEmptyString was called with an INVALID String.
  input: ""
  check: input.nonEmpty
  ———————————————————————————————————————————————————————————————————————————

Integrations

Neotype integrates with the following libraries.

• zio-json
• zio-config
• tapir
• quill
• circe

ZIO Json Example

import neotype.*
import neotype.ziojson.*
import zio.json.*

type NonEmptyString = NonEmptyString.Type
given NonEmptyString: Newtype[String] with
  inline def validate(value: String): Boolean = value.nonEmpty
  override inline def failureMessage = "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.*, we automatically generate a JsonCodec for NonEmptyString. Custom failure messages are also supported (by overriding def failureMessage in the Newtype definition).