scala - Scala/Play 的语法和含义!代码示例

Question

我有以下 斯卡拉/玩! 代码:

case class Tweet(from: String, text: String)

implicit val tweetReads = (
 (JsPath \ "from_user_name").read[String] ~
 (JsPath \ "text").read[String]) (Tweet.apply _)

我有 关于上述代码的语法和含义的几个问题 :

~ 在哪个类/对象上方法调用？

Tweet.apply 的参数的类/类型是什么？ ?

编辑 1 :完整的源代码:

package models

import play.api.libs.json._
import play.api.libs.json.util._
import play.api.libs.json.Reads._
import play.api.libs.json.Writes._
import play.api.libs.functional.syntax._

case class Tweet(from: String, text: String)

object Tweet {

  implicit val tweetReads = (
      (JsPath \ "from_user_name").read[String] ~
      (JsPath \ "text").read[String])(Tweet.apply _)

  implicit val tweetWrites = (
    (JsPath \ "from").write[String] ~
    (JsPath \ "text").write[String])(unlift(Tweet.unapply))
}

Answer 1

一步步:

方法\在对象 JsPath 上

val path1: JsPath = JsPath \ "from_user_name"
val path2: JsPath = JsPath \ "text"

方法 read在 JsPath 类型的对象上

val reads1: Reads[String] = path1.read[String]
val reads2: Reads[String] = path2.read[String]

没有方法 ~在 Reads ，但在 FunctionalBuilderOps 中有这样的方法并且存在来自 M[T] 的隐式转换至 FunctionalBuilderOps[M[_], T]在 play.api.libs.functional.syntax - toFunctionalBuilderOps .

val reads1FunctionalBuilderOps: FunctionalBuilderOps[Reads, String] =
  toFunctionalBuilderOps(reads1)

val canBuild2: CanBuild2[String, String] = reads1FunctionalBuilderOps.~(reads2)

Tweet.apply _是用于创建 FunctionN 的 Scala 语法使用方法与 N论据:

val func: (String, String) => Tweet = Tweet.apply _

有一个 apply CanBuild2[A, B] 中的方法.它接受 (A, B) => C并返回 Reads[C] (在这种情况下):

implicit val tweetReads: Reads[Tweet] = canBuild2.apply(func)

其实 JsPath#read中也有隐式参数, toFunctionalBuilderOps和 CanBuild2#apply方法。使用该参数:

val reads1: Reads[String] = path1.read[String](Reads.StringReads)

...
val reads1FunctionalBuilderOps: FunctionalBuilderOps[Reads, String] =
  toFunctionalBuilderOps(reads1)(
    functionalCanBuildApplicative(
      Reads.applicative(JsResult.applicativeJsResult)))

...
implicit val tweetReads: Reads[Tweet] =
  canBuild2.apply(func)(functorReads)