未找到隐式参数

Question

我在编写一个问题时遇到了一些麻烦，为什么编译器会抱怨找不到读取的隐式参数，因为我几乎可以确定它是否在范围内。错误如下：

错误：（13，18）找不到类型为Config的Json解串器。尝试实现此类型的隐式读取或格式。 test.validate [配置] .MAP { ^

错误：（13，18）不够论据方法验证：（隐式RDS：play.api.libs.json.Reads [配置]）play.api .libs.json.JsResult [wings.m2m.conf.model.Config]。 未指定的值参数rds。 test.validate [配置] .MAP { ^

和它发生在以下代码：执行所述测试对象上的主要方法时，会发生

import play.api.libs.json._ 
import play.api.libs.json.Reads._ 
import Config.JsonImplicits._ 

import scala.util.Try 

object Test { 
    def main(args: Array[String]) { 

    val test = Json.obj("action" -> Config.Action.nameAcquisitionRequest.toString, "value" -> "hola") 
    test.validate[Config].map { 
     t => println(t) 
     t 
    } 
    } 
} 

/** 
* Config companion object 
*/ 
object Config { 

    type ValueType = String 

    val ActionKey = "action" 

    val ValueKey = "value" 

    object Action extends Enumeration { 

    type Action = Value 

    val nameAcquisitionRequest = Value("nameAcquisitionRequest") 
    val nameAcquisitionReject = Value("nameAcquisitionReject") 
    val nameAcquisitionAck = Value("nameAcquisitionAck") 

    val broadcast = Value("broadcast") 

    } 

    /** 
    * Json implicit conversions 
    */ 
    object JsonImplicits { 

    implicit object ConfigReads extends Reads[Config] { 

     def hTypeCast(action: Config.Action.Value, value: Config.ValueType): Config = { 
     action match { 
      case Config.Action.nameAcquisitionRequest => NameAcquisitionRequest(value) 
      case Config.Action.nameAcquisitionReject => NameAcquisitionReject(value) 
      case Config.Action.nameAcquisitionAck => NameAcquisitionAck(value) 
     } 
     } 

     override def reads(json: JsValue): JsResult[Config] = json match { 
      case json: JsObject => 
      val action = (json \ ActionKey).as[String] 
      Try(Config.Action.withName(action)) map { 
       a => 
       val value = (json \ ValueKey).as[String] 
       JsSuccess(hTypeCast(a, value)) 
      } getOrElse (JsError("Can't convert to Config")) 
      case _ => JsError("Can't convert to Config") 
     } 
     } 


    implicit object ConfigWrites extends OWrites[Config] { 

     def jsObjectCreator(action: Config.Action.Value, value: Config.ValueType): JsObject = { 
     Json.obj(ActionKey -> action.toString, ValueKey -> Json.toJson(value)) 
     } 

     override def writes(o: Config): JsObject = o match { 
     case c: NameAcquisitionRequest => jsObjectCreator(Config.Action.nameAcquisitionRequest, c.value) 
     case c: NameAcquisitionReject => jsObjectCreator(Config.Action.nameAcquisitionReject, c.value) 
     case c: NameAcquisitionAck => jsObjectCreator(Config.Action.nameAcquisitionAck, c.value) 
     } 
    } 
    } 

} 

sealed trait Config { 
    val value: Config.ValueType 
} 

/** 
* Intermediate config message 
* @param value 
*/ 
case class NameAcquisitionRequest(override val value: String) 
    extends Config 

case class NameAcquisitionReject(override val value: String) 
    extends Config 

case class NameAcquisitionAck(override val value: String) 
    extends Config 

case class Broadcast(override val value: String) 
    extends Config 

的误差。为了使这个例子工作，请确保在SBT中添加以下依赖项：“com.typesafe.play”%%“play-json”％“2.4.1”。我不确定，但可能需要解析器：解析器+ =“类型安全回购”在“http://repo.typesafe.com/typesafe/releases/”

Answer 1

我不确定你试图达到什么目的，是否解决了你的问题，但是在这里你去了：

test.validate[Config](Config.JsonImplicits.ConfigReads).map { 
    t => println(t) 
    t 
}