REGISTRY.md

AccessorRegistry

The AccessorRegistry gives you a way of 'pickling' objects based on their underlying type. Unlike when using the accessors implicitly, this requires a runtime lookup of the class type of a serialized/deserialized object to locate the accessor. This can be especially handy in message-passing systems that may need to marshal a blob without knowing its source/destination type. When combined with pattern matching, this can provide you with an actor-like message passing system.

scala> import json._
import json._

scala> import json.tools.AccessorRegistry
import json.tools.AccessorRegistry

scala> @accessor case class TestClass(a: Int, b: Option[Int], c: String = "", d: Option[Int] = None)
defined object TestClass
defined class TestClass

scala> AccessorRegistry.add[TestClass]

The AccessorRegistry also exposes itself as a selfless trait if you would like to encapsulate your own registry.

scala> object MyRegistry extends AccessorRegistry
defined object MyRegistry

scala> MyRegistry.add[TestClass]

You can also add singleton objects (these are bound by their name classname, case objects work best)

scala> case object StartCommand
defined object StartCommand

scala> MyRegistry.add(StartCommand)

The AccessorRegistry also provides an accessor for the Scala type Any. When used carefully, this can allow you to serialize to and from the type Any assuming the base types have been registered in the AccessorRegistry.

scala> case class Envelope(msg: Any)
defined class Envelope

scala> implicit val envAccessor = {
     |   import AccessorRegistry.anyAccessor //or MyRegistry.anyAccessor if using your own registry
     |   ObjectAccessor.create[Envelope]
     | }
envAccessor: json.internal.CaseClassObjectAccessor[Envelope] = CaseClassObjectAccessor

scala> AccessorRegistry.add[Envelope]

scala> val inst = Envelope(TestClass(1, None))
inst: Envelope = Envelope(TestClass(1,None,,None))

scala> val regularJS = inst.js
regularJS: json.JObject =
{
  "msg": {
    "data": {
      "a": 1,
      "b": null,
      "c": "",
      "d": null
    },
    "class": "TestClass"
  }
}

scala> val pickeledJS = inst.js(AccessorRegistry.anyAccessor)
pickeledJS: json.JValue =
{
  "data": {
    "msg": {
      "data": {
        "a": 1,
        "b": null,
        "c": "",
        "d": null
      },
      "class": "TestClass"
    }
  },
  "class": "Envelope"
}

scala> require(pickeledJS.toObject[Any](AccessorRegistry.anyAccessor) == inst)

scala> require(regularJS.toObject[Envelope] == inst)