Value.scala

/*
 Conditional function application.

 !!!NOTE!!!
 This not equivalent to PartialFunction as it applies a Function from T => T. The intention is to update T, not to transform.
 Thus not to be used as replacement of PartialFunction.
 
 Useful when we need to apply different conditional updates and 
 track if the value was changed or not at the end.
*/
object pack {
  sealed trait Value[T] {

    def get: T

    def when[A](pred: => Boolean)(func: T => T): Value[T] = {
      if (pred) Changed(func(get)) else this
    }

  }
  object Value {
    def apply[T](any: T): Value[T] = Unchanged(any)

    implicit class ValueWrap[A](any: A) {
      def when(pred: => Boolean)(func: A => A): Value[A] =
        Value(any).when(pred)(func)
    }
  }

  case class Changed[T](get: T) extends Value[T]
  case class Unchanged[T](get: T) extends Value[T]
} 

case class Person(name: String, age: Int)

import pack._
import pack.Value._


val myself = Person(name = "Renato", age = 41)


  myself
    .when(true) {
      _.copy(name = "Renato Cavalcanti")
    }
    .when(false) {
      _.copy(age = 42)
    }

  myself
    .when(false) {
      _.copy(name = "Renato Cavalcanti")
    }
    .when(false) {
      _.copy(age = 42)
    }

defined object pack
defined class Person
import pack._
import pack.Value._
myself: Person = Person(Renato,41)
res31: Person = Person(Renato,41)
res32: pack.Value[Person] = Changed(Person(Renato Cavalcanti,41))
res33: pack.Value[Person] = Changed(Person(Renato Cavalcanti,41))
res34: Person = Person(Renato,41)
res35: pack.Value[Person] = Unchanged(Person(Renato,41))
res36: pack.Value[Person] = Unchanged(Person(Renato,41))