scala smart constructor / published by https://github.com/dacr/code-examples-manager #9ca3d9cf-3f2b-4bbe-aa44-83c5696859d3/66eea4aff1edaa6d731c2b1a245234afbfb14648

scala-feature-smart-constructor.sc

// summary : scala smart constructor
// keywords : scala, adt, language-feature, smart-constructor, @testable
// publish : gist
// authors : David Crosson
// license : Apache License Version 2.0 (https://www.apache.org/licenses/LICENSE-2.0.txt)
// id : 9ca3d9cf-3f2b-4bbe-aa44-83c5696859d3
// created-on : 2021-04-05T16:56:55Z
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala "3.4.2"
// ---------------------

// written after [John De Goes - 12 Steps To Better Scala (Part I)](https://youtu.be/71yhnTGw0hY)

// ----------------------------------------------------------------
// Smart constructor to make it impossible to define illegal state
// See also :
// - https://github.com/fthomas/refined
// - http://fthomas.github.io/talks/2016-05-04-refined
// - https://kwark.github.io/refined-in-practice/

sealed abstract case class Email private(value: String)

object Email {
  def checkEmail(input:String):Boolean = {
    // https://howtodoinjava.com/java/regex/java-regex-validate-email-address/
    input.matches("^[a-zA-Z0-9_!#$%&’*+/=?`{|}~^.-]+@[a-zA-Z0-9.-]+$")
  }
  def fromString(value: String):Option[Email] = {
    if (checkEmail(value)) Some(new Email(value){})
    else None
  }
}

// The only way to create email instances...
val email = Email.fromString("[email protected]")
email.foreach(println)