Lens の実用例

build.sbt

import sbt._

name := "monocle-template"

scalaVersion := "2.11.8"

licenses := Seq("MIT License" -> url("http://opensource.org/licenses/mit"))

scalacOptions ++= Seq(
  "-deprecation",
  "-feature",
  "-Xlint",
  "-Ywarn-dead-code",
  "-language:higherKinds",
  "-language:postfixOps",
  "-language:implicitConversions"
)

resolvers += Resolver.sonatypeRepo("releases")
resolvers += Resolver.sonatypeRepo("snapshots")

val libraryVersion = "1.2.2"

libraryDependencies ++= Seq(
  "com.github.julien-truffaut"  %%  "monocle-core"    % libraryVersion,
  "com.github.julien-truffaut"  %%  "monocle-generic" % libraryVersion,
  "com.github.julien-truffaut"  %%  "monocle-macro"   % libraryVersion,
  "com.github.julien-truffaut"  %%  "monocle-state"   % libraryVersion,
  "com.github.julien-truffaut"  %%  "monocle-law"     % libraryVersion  % "test"
)

// for @Lenses macro support
addCompilerPlugin("org.scalamacros" %% "paradise" % "2.1.0" cross CrossVersion.full)

data.scala

val data = CampaignStatus(
  999L,
  MonthlyStatus(
    Win(CPM(2000)),
    Bid(CPM(2000))),
  DailyStatus(
    Win(CPM(1000)),
    Bid(CPM(1000))),
  List("http://example.com"),
  new Date()
)

val data1 = newCampaignStatus(999L, new Date())
  .setMonthlyWinStatus(1000)
  .setDailyWinStatus(100)
  .addUrl("http://example.com")
  .addUrl("http://example.org")

val data2 = data1
  .modifyMonthlyWinStatus(_ * 2)
  .modifyDailyWinStatus(_ * 2)

val data3 = newCampaignStatus(999L, new Date())
  .dailyBidStatusLens.set(100)
  .dailyBidStatusLens.modify(_ + 200)

dsl.scala

import java.util.Date

import monocle.Lens
import monocle.macros.GenLens
import monocle.function.all._
import monocle.syntax.apply._

object CampaignStatusBuilder {

  def newCampaignStatus(id: Long, readAt: Date): CampaignStatus =
    CampaignStatus(
      id,
      MonthlyStatus(
        Win(CPM(0)),
        Bid(CPM(0))),
      DailyStatus(
        Win(CPM(0)),
        Bid(CPM(0))),
      List.empty[String],
      readAt
    )

  implicit def toCampaignStatusBuilder(status: CampaignStatus): CampaignStatusBuilder =
    new CampaignStatusBuilder(status)


  lazy val _dailyStatus = GenLens[CampaignStatus](_.dailyStatus)
  lazy val _bid = GenLens[DailyStatus](_.bid)
  lazy val _cpm = GenLens[Bid](_.cpm)
  lazy val _value = GenLens[CPM](_.value)
}

class CampaignStatusBuilder(status: CampaignStatus) {
  import CampaignStatusBuilder._

  // === copy method

  def modifyMonthlyWinStatus(f: Long => Long): CampaignStatus =
    status.copy(
      monthlyStatus = status.monthlyStatus.copy(
        win = status.monthlyStatus.win.copy(
          cpm = status.monthlyStatus.win.cpm.copy(
            value = f(status.monthlyStatus.win.cpm.value)
          )
        )
      )
    )

  def setMonthlyWinStatus(v: Long): CampaignStatus =
    modifyMonthlyWinStatus(_ => v)

  // === lens

  def modifyDailyWinStatus(f: Long => Long): CampaignStatus =
    GenLens[CampaignStatus](_.dailyStatus.win.cpm.value).modify(f)(status)

  def setDailyWinStatus(v: Long): CampaignStatus =
    status &|-> GenLens[CampaignStatus](_.dailyStatus.win.cpm.value) set v

  def addUrl(url: String): CampaignStatus =
    status &|-> GenLens[CampaignStatus](_.urls) modify (url :: _)


  def dailyBidStatusLens =
    status &|-> _dailyStatus ^|-> _bid ^|-> _cpm ^|-> _value
}

entity.scala

import java.util.Date

case class CampaignStatus(
  id:            Long,
  monthlyStatus: MonthlyStatus,
  dailyStatus:   DailyStatus,
  urls:          List[String],
  readAt:        Date
)

case class MonthlyStatus(win: Win, bid: Bid)
case class DailyStatus(win: Win, bid: Bid)

case class Win(cpm: CPM)
case class Bid(cpm: CPM)

case class CPM(value: Long)