Packages

trait Unapply[TC[_[_]], MA] extends AnyRef

Represents a type MA that has been destructured into as a type constructor M[_] applied to type A, along with a corresponding type class instance TC[M].

The implicit conversions in the companion object provide a means to obtain type class instances for partially applied type constructors, in lieu of direct compiler support as described in SI-2712.

// Directly depending on Applicative[G]
def traverse[G[_], B](f: A => G[B])(implicit G: Applicative[G]): G[F[B]] =
  G.traverse(self)(f)

// Indirect lookup of the Applicative instance
def traverseI[GB](f: A => GB)(implicit G: Unapply[Applicative, GB]): G.M[F[G.A]] /*G[F[B]*/ = {
  G.TC.traverse(self)(a => G(f(a)))
}

// Deforested version of traverseI
def traverseI2[GB](f: A => GB)(implicit G: Unapply[Applicative, GB]): G.M[F[G.A]] /*G[F[B]*/ = {
  G.TC.traverse(self)(G.leibniz.onF(f))
}

// Old usage
def stateTraverse1 {
  import scalaz._, Scalaz._
  import State.{State, stateMonad}
  val ls = List(1, 2, 3)
  val traverseOpt: Option[List[Int]] = ls.traverse(a => Some(a))
  val traverseState: State[Int, List[Int]] = ls.traverse[State[Int, ?], Int](a => State((x: Int) => (x + 1, a)))
}

// New usage
def stateTraverse2 {
  import scalaz._, Scalaz._
  val ls = List(1, 2, 3)
  val traverseOpt: Option[List[Int]] = ls.traverseI(a => some(a))
  val traverseState = ls.traverseI(a => State((x: Int) => (x + 1, a)))
}

Credits to Miles Sabin.

Annotations
@implicitNotFound( ... )
Source
Unapply.scala
Linear Supertypes
AnyRef, Any
Ordering
  1. Alphabetic
  2. By Inheritance
Inherited
  1. Unapply
  2. AnyRef
  3. Any
  1. Hide All
  2. Show All
Visibility
  1. Public
  2. All

Type Members

  1. abstract type A

    The type that M was applied to

  2. abstract type M[_]

    The type constructor

Abstract Value Members

  1. abstract def TC: TC[M]

    The instance of the type class

  2. abstract def leibniz: ===[MA, M[A]]

    Evidence that MA =:= M[A]

Concrete Value Members

  1. final def apply(ma: MA): M[A]

    Compatibility.

    Compatibility.

    Annotations
    @inline()