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/*
* scala-exercises - exercises-monocle
* Copyright (C) 2015-2016 47 Degrees, LLC. <http://www.47deg.com>
*/
package monocle
import monocle.macros.GenIso
import org.scalatest._
import org.scalaexercises.definitions._
object IsoHelper {
case class Person(name: String, age: Int)
val personToTuple = Iso[Person, (String, Int)](p => (p.name, p.age)) {
case (name, age) => Person(name, age)
}
def listToVector[A] = Iso[List[A], Vector[A]](_.toVector)(_.toList)
def vectorToList[A] = listToVector[A].reverse
val stringToList = Iso[String, List[Char]](_.toList)(_.mkString(""))
case class MyString(s: String)
case class Foo()
case object Bar
}
/** == Iso ==
*
* An [[http://julien-truffaut.github.io/Monocle/optics/iso.html `Iso`]] is an optic which converts elements of type `S` into elements of type `A` without loss.
*
* Consider a case class Person with two fields:
*
* {{{
* case class Person(name: String, age: Int)
* }}}
*
* @param name iso
*/
object IsoExercises extends FlatSpec with Matchers with Section {
import IsoHelper._
/**
* `Person` is equivalent to a tuple `(String, Int)` and a tuple `(String, Int)` is equivalent to `Person`. So we can create an `Iso` between `Person` and `(String, Int)` using two total functions:
*
* - `get: Person => (String, Int)`
* - `reverseGet (aka apply): (String, Int) => Person`
*
* {{{
* import monocle.Iso
* val personToTuple = Iso[Person, (String, Int)](p => (p.name, p.age)){case (name, age) => Person(name, age)}
* }}}
*/
def exercisePersonToTuple(res0: (String, Int), res1: Person) = {
personToTuple.get(Person("Zoe", 25)) should be(res0)
personToTuple.reverseGet(("Zoe", 25)) should be(res1)
}
/**
* Or simply:
*/
def exercisePersonToTupleApply(res0: Person) =
personToTuple(("Zoe", 25)) should be(res0)
/**
* Another common use of `Iso` is between collection. `List` and `Vector` represent the same concept, they are both an ordered sequence of elements but they have different performance characteristics. Therefore, we can define an `Iso` between a `List[A]` and a `Vector[A]`:
* {{{
* def listToVector[A] = Iso[List[A], Vector[A]](_.toVector)(_.toList)
* }}}
*/
def exerciseListToVector(res0: Vector[Int]) =
listToVector.get(List(1, 2, 3)) should be(res0)
/**
* We can also `reverse` an `Iso` since it defines a symmetric transformation:
* {{{
* def vectorToList[A] = listToVector[A].reverse
* // vectorToList: [A]=> monocle.PIso[Vector[A],Vector[A],List[A],List[A]]
* }}}
*/
def exerciseVectorToList(res0: List[Int]) =
vectorToList.get(Vector(1, 2, 3)) should be(res0)
/**
* `Iso` are also convenient to lift methods from one type to another, for example a `String` can be seen as a `List[Char]` so we should be able to transform all functions `List[Char] => List[Char]` into `String => String`:
* {{{
* val stringToList = Iso[String, List[Char]](_.toList)(_.mkString(""))
* }}}
*/
def exerciseStringToList(res0: String) =
stringToList.modify(_.tail)("Hello") should be(res0)
/**
* We defined several macros to simplify the generation of Iso between a case class and its Tuple equivalent. All macros are defined in a separate module (see modules).
* {{{
* case class MyString(s: String)
* case class Foo()
* case object Bar
*
* import monocle.macros.GenIso
* }}}
*
* First of all, `GenIso.apply` generates an `Iso` for `newtype` i.e. case class with a single type parameter:
*/
def exerciseGenIsoApply(res0: String) =
GenIso[MyString, String].get(MyString("Hello")) should be(res0)
/**
* Then, `GenIso.unit` generates an `Iso` for object or case classes with no field:
*
* {{{
* GenIso.unit[Foo]
* // res8: monocle.Iso[Foo,Unit] = monocle.PIso$$anon$10@280a5b3b
* GenIso.unit[Bar.type]
* // res9: monocle.Iso[Bar.type,Unit] = monocle.PIso$$anon$10@5520ac34
* }}}
*
* Finally, `GenIso.fields` is a whitebox macro which generalise `GenIso.apply` to all case classes:
*/
def exerciseGenIsoFields(res0: (String, Int)) =
GenIso.fields[Person].get(Person("John", 42)) should be(res0)
/**
* Be aware that whitebox macros are not supported by all IDEs.
*
* == Laws ==
*
* An `Iso` must satisfy all properties defined in `IsoLaws` from the core module. You can check the validity of your own `Iso` using `IsoTests` from the law module.
*
* In particular, an Iso must verify that `get` and `reverseGet` are inverse. This is done via `roundTripOneWay` and `roundTripOtherWay` laws:
*
*/
def exerciseLaws(res0: Boolean, res1: Boolean) = {
personToTuple.get(Person("Zoe", 25))
def roundTripOneWay[S, A](i: Iso[S, A], s: S): Boolean =
i.reverseGet(i.get(s)) == s
def roundTripOtherWay[S, A](i: Iso[S, A], a: A): Boolean =
i.get(i.reverseGet(a)) == a
roundTripOneWay(personToTuple, Person("Zoey", 25)) should be(res0)
roundTripOtherWay(personToTuple, ("Zoe", 52)) should be(res1)
}
}