斯卡拉酸洗：爲嵌套結構寫一個自定義的pickler/unpickler

Question

我想寫一個自定義的SPickler/Unpickler對來解決當前scala-pickling的侷限性。 我試圖pickle的數據類型是一個case類，其中一些字段已經有自己的SPickler和Unpickler實例。 我想在我的自定義pickler中使用這些實例，但我不知道如何。

這裏是我的意思的例子：

// Here's a class for which I want a custom SPickler/Unpickler. 
// One of its fields can already be pickled, so I'd like to reuse that logic. 
case class MyClass[A: SPickler: Unpickler: FastTypeTag](myString: String, a: A) 

// Here's my custom pickler. 
class MyClassPickler[A: SPickler: Unpickler: FastTypeTag](
    implicit val format: PickleFormat) extends SPickler[MyClass[A]] with Unpickler[MyClass[A]] { 
    override def pickle(
    picklee: MyClass[A], 
    builder: PBuilder) { 
    builder.beginEntry(picklee) 

    // Here we save `myString` in some custom way. 
    builder.putField(
     "mySpecialPickler", 
     b => b.hintTag(FastTypeTag.ScalaString).beginEntry(
     picklee.myString).endEntry()) 

    // Now we need to save `a`, which has an implicit SPickler. 
    // But how do we use it? 

    builder.endEntry() 
    } 

    override def unpickle(
    tag: => FastTypeTag[_], 
    reader: PReader): MyClass[A] = { 
    reader.beginEntry() 

    // First we read the string. 
    val myString = reader.readField("mySpecialPickler").unpickle[String] 

    // Now we need to read `a`, which has an implicit Unpickler. 
    // But how do we use it? 
    val a: A = ??? 

    reader.endEntry() 

    MyClass(myString, a) 
    } 
} 

我真的很感激，工作的例子。 謝謝！

Answer 1

這裏是一個工作示例：

case class MyClass[A](myString: String, a: A) 

注意的MyClass類型參數不需要背景下邊界。只有自定義的pickler類需要相應的implicits：

class MyClassPickler[A](implicit val format: PickleFormat, aTypeTag: FastTypeTag[A], 
            aPickler: SPickler[A], aUnpickler: Unpickler[A]) 
    extends SPickler[MyClass[A]] with Unpickler[MyClass[A]] { 

    private val stringUnpickler = implicitly[Unpickler[String]] 

    override def pickle(picklee: MyClass[A], builder: PBuilder) = { 
    builder.beginEntry(picklee) 

    builder.putField("myString", 
     b => b.hintTag(FastTypeTag.ScalaString).beginEntry(picklee.myString).endEntry() 
    ) 

    builder.putField("a", 
     b => {  
     b.hintTag(aTypeTag) 
     aPickler.pickle(picklee.a, b) 
     } 
    ) 

    builder.endEntry() 
    } 

    override def unpickle(tag: => FastTypeTag[_], reader: PReader): MyClass[A] = { 
    reader.hintTag(FastTypeTag.ScalaString) 
    val tag = reader.beginEntry() 
    val myStringUnpickled = stringUnpickler.unpickle(tag, reader).asInstanceOf[String] 
    reader.endEntry() 

    reader.hintTag(aTypeTag) 
    val aTag = reader.beginEntry() 
    val aUnpickled = aUnpickler.unpickle(aTag, reader).asInstanceOf[A] 
    reader.endEntry() 

    MyClass(myStringUnpickled, aUnpickled) 
    } 

} 

除了定製皮克勒類，我們還需要返回專門用於具體類型參數的皮克勒實例隱式高清：

implicit def myClassPickler[A: SPickler: Unpickler: FastTypeTag](implicit pf: PickleFormat) = 
    new MyClassPickler