Validated Newtypes

As of version 0.18.23 and above, Smithy4s has the ability to render constrained newtypes over Smithy primitives as "validated" classes in the code it generates. In practice, this means that a newtype will now have an apply method that returns either a validated value or an error.

The way to utilize this feature is through your Smithy specifications by adding a file with the following content to your Smithy sources:

$version: "2"

metadata smithy4sRenderValidatedNewtypes = true

Alternatively, if you want to generate validated newtypes only for select shapes in your model, you can accomplish this using the smithy4s.meta#validateNewtype trait. This trait can only be used on number shapes with a range constraint or string shapes with pattern and/or length constraints.

use smithy4s.meta#validateNewtype

@validateNewtype
@length(min: 5)
string Name

Below is the generated scala class that Smithy4s will generate:

import smithy4s._
import smithy4s.schema.Schema.string

type Name = Name.Type

object Name extends ValidatedNewtype[String] {
  val id: ShapeId = ShapeId("smithy4s.example", "Name")

  val hints: Hints = Hints.empty

  val underlyingSchema: Schema[String] = 
    string
      .withId(id)
      .addHints(hints)
      .validated(smithy.api.Length(min = Some(5L), max = None))

  val validator: Validator[String, Name] = 
    Validator.of[String, Name](Bijection[String, Name](_.asInstanceOf[Name], value(_)))
      .validating(smithy.api.Length(min = Some(5L), max = None))

  implicit val schema: Schema[Name] = validator.toSchema(underlyingSchema)

  @inline def apply(a: String): Either[String, Name] = validator.validate(a)
}