針對implicits和排序問題的更好解決方法，同時使用Spray序列化爲JSON？

Question

我正在使用Spray JSON庫將我們的案例類序列化爲JSON。問題是我們有一些相互遞歸的定義。我正在從這個序列化密封特徵的例子開始工作： http://www.cakesolutions.net/teamblogs/2012/11/30/spray-json-and-adts/

下面是一個簡單的例子。請注意C的定義：

import spray.json._ 
import DefaultJsonProtocol._ 

sealed trait BaseTrait 
sealed trait SpecializedTrait extends BaseTrait 

case class A(argA: BaseTrait, foo: Int) extends SpecializedTrait 
case class B(argB: BaseTrait, foo: Int) extends SpecializedTrait 

case class C(foo: Int) extends BaseTrait 

object BaseTrait { 
    implicit val cJsonFormat = jsonFormat1(C) 

    implicit object BaseTraitJsonFormat extends RootJsonFormat[BaseTrait] { 
    override def write(obj: BaseTrait): JsValue = throw new IllegalStateException("Not Implemented") 
    override def read(v: JsValue): BaseTrait = throw new IllegalStateException("Not Implemented") 
    } 
} 

object SpecializedTrait { 
    implicit val aJsonFormat = jsonFormat2(A) 
    implicit val bJsonFormat = jsonFormat2(B) 

    implicit object SpecializedTraitJsonFormat extends RootJsonFormat[SpecializedTrait] { 
    override def write(obj: SpecializedTrait): JsValue = throw new IllegalStateException("Not Implemented") 
    override def read(v: JsValue): SpecializedTrait = throw new IllegalStateException("Not Implemented") 
    } 
} 

當你改變「C」的定義，原來相互遞歸定義。

... 
case class C(argC: SpecializedTrait, foo: Int) extends BaseTrait 

object BaseTrait { 
    implicit val cJsonFormat = jsonFormat2(C) 

... 

現在顯然，你不能只是說不，我不能有相互遞歸的數據結構。由於隱式對象的解析規則，編譯器似乎陷入了困境。

是否有解決方法？我周圍有改變的對象匿名類的聲明，即

import spray.json._ 
import DefaultJsonProtocol._ 

sealed trait BaseTrait 
sealed trait SpecializedTrait extends BaseTrait 

case class A(argA: BaseTrait, foo: Int) extends SpecializedTrait 
case class B(argB: BaseTrait, foo: Int) extends SpecializedTrait 

case class C(argC: SpecializedTrait, foo: Int) extends BaseTrait 

object BaseTrait { 
    implicit val cJsonFormat : RootJsonFormat[C] = jsonFormat2(C) 

    implicit val baseTraitFormat : RootJsonFormat[BaseTrait] = new RootJsonFormat[BaseTrait] { 
    def write(obj: BaseTrait): JsValue = throw new IllegalStateException("Not Implemented") 
    def read(v: JsValue): BaseTrait = throw new IllegalStateException("Not Implemented") 
    } 
} 

object SpecializedTrait { 
    implicit val aJsonFormat : RootJsonFormat[A] = jsonFormat2(A) 
    implicit val bJsonFormat : RootJsonFormat[B] = jsonFormat2(B) 

    implicit val specializedTraitFormat : RootJsonFormat[SpecializedTrait] = new RootJsonFormat[SpecializedTrait] { 
    override def write(obj: SpecializedTrait): JsValue = throw new IllegalStateException("Not Implemented") 
    override def read(v: JsValue): SpecializedTrait = throw new IllegalStateException("Not Implemented") 
    } 
} 

這最後片斷工作，注意從「隱式對象」到「隱VAL」和隨後的匿名類的變化。

Answer 1

按順序定義implicits並將它們放入一個對象中。

import spray.json._ 
import DefaultJsonProtocol._ 

sealed trait BaseTrait 
sealed trait SpecializedTrait extends BaseTrait 

case class A(argA: BaseTrait, foo: Int) extends SpecializedTrait 
case class B(argB: BaseTrait, foo: Int) extends SpecializedTrait 
case class C(argC: SpecializedTrait, foo: Int) extends BaseTrait 

object SomeProtocol { 
    implicit object BaseTraitJsonFormat extends RootJsonFormat[BaseTrait] { 
    override def write(obj: BaseTrait): JsValue = throw new IllegalStateException("Not Implemented") 
    override def read(v: JsValue): BaseTrait = throw new IllegalStateException("Not Implemented") 
    } 
    implicit object SpecializedTraitJsonFormat extends RootJsonFormat[SpecializedTrait] { 
    override def write(obj: SpecializedTrait): JsValue = throw new IllegalStateException("Not Implemented") 
    override def read(v: JsValue): SpecializedTrait = throw new IllegalStateException("Not Implemented") 
    } 
    implicit val aJsonFormat = jsonFormat2(A) 
    implicit val bJsonFormat = jsonFormat2(B) 
    implicit val cJsonFormat = jsonFormat2(C) 
}