From 20afa757f499688b56cbd6b8571014b75d6d4dce Mon Sep 17 00:00:00 2001
From: Jakob Odersky <jakob@odersky.com>
Date: Thu, 2 Aug 2018 15:24:52 -0700
Subject: Treat value classes transparently

---
 shared/src/main/scala/DerivedFormats.scala | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

(limited to 'shared/src/main/scala/DerivedFormats.scala')

diff --git a/shared/src/main/scala/DerivedFormats.scala b/shared/src/main/scala/DerivedFormats.scala
index f6a3f7b..ed39f46 100644
--- a/shared/src/main/scala/DerivedFormats.scala
+++ b/shared/src/main/scala/DerivedFormats.scala
@@ -24,18 +24,24 @@ trait DerivedFormats { self: BasicFormats =>
 
   def combine[T](ctx: CaseClass[JsonFormat, T]): JsonFormat[T] =
     new JsonFormat[T] {
-      override def write(value: T): JsValue = {
-        val fields: Seq[(String, JsValue)] = ctx.parameters.collect {
-          case param
-              if !param.option || param.dereference(value) != None || printNull =>
-            extractFieldName(param.label) -> param.typeclass.write(
-              param.dereference(value)
-            )
+      override def write(value: T): JsValue =
+        if (ctx.isValueClass) {
+          val param = ctx.parameters.head
+          param.typeclass.write(param.dereference(value))
+        } else {
+          val fields: Seq[(String, JsValue)] = ctx.parameters.collect {
+            case param
+                if !param.option || param.dereference(value) != None || printNull =>
+              extractFieldName(param.label) -> param.typeclass.write(
+                param.dereference(value)
+              )
+          }
+          JsObject(fields: _*)
         }
-        JsObject(fields: _*)
-      }
 
       override def read(value: JsValue): T = value match {
+        case js if ctx.isValueClass =>
+          ctx.construct(param => param.typeclass.read(value))
         case obj: JsObject =>
           if (ctx.isObject) {
             ctx.rawConstruct(Seq.empty)
-- 
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