From 1ea072197cf8a992b37d7efe0636358a236b9d6d Mon Sep 17 00:00:00 2001
From: Jon Pretty <jon.pretty@propensive.com>
Date: Sun, 11 Jun 2017 21:36:32 +0200
Subject: Appears to be working for both covariant and contravariant
 typeclasses

---
 examples/src/main/scala/example.scala | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

(limited to 'examples')

diff --git a/examples/src/main/scala/example.scala b/examples/src/main/scala/example.scala
index e61f8bd..c719ad8 100644
--- a/examples/src/main/scala/example.scala
+++ b/examples/src/main/scala/example.scala
@@ -30,10 +30,10 @@ object Extractor extends Extractor_1 {
   implicit val stringExtractor: Extractor[String] = Extractor(_.str)
   implicit val doubleExtractor: Extractor[Double] = Extractor(_.str.length.toDouble)
 
-  implicit val dereferencer: Dereferencer[Extractor] { type Value = Thing } = new Dereferencer[Extractor] {
+  implicit val derivation: CovariantDerivation[Extractor] { type Value = Thing } = new CovariantDerivation[Extractor] {
     type Value = Thing
     def dereference(value: Thing, param: String): Thing = value.access(param)
-    def delegate[T](extractor: Extractor[T], value: Thing): T = extractor.extract(value)
+    def call[T](extractor: Extractor[T], value: Thing): T = extractor.extract(value)
     def combine[Supertype, Right <: Supertype](left: Extractor[_ <: Supertype],
         right: Extractor[Right]): Extractor[Supertype] = left.orElse(right)
     
@@ -41,7 +41,6 @@ object Extractor extends Extractor_1 {
       def extract(source: Thing): T = body(source)
     }
   }
-
 }
 
 trait Extractor_1 extends Extractor_2 {
@@ -49,6 +48,36 @@ trait Extractor_1 extends Extractor_2 {
     def extract(source: Thing): List[T] = List(implicitly[Extractor[T]].extract(source))
   }
 }
+
 trait Extractor_2 {
   implicit def generic[T]: Extractor[T] = macro Macros.magnolia[T, Extractor[_]]
 }
+
+trait Serializer[T] {
+  def serialize(src: T): String
+}
+
+object Serializer extends Serializer_1 {
+  implicit val deriv: ContravariantDerivation[Serializer] { type Return = String } = new ContravariantDerivation[Serializer] {
+    type Return = String
+    def call[T](typeclass: Serializer[T], value: T): String = typeclass.serialize(value)
+    def construct[T](body: T => String): Serializer[T] = new Serializer[T] {
+      def serialize(value: T): String = body(value)
+    }
+    def join(xs: List[String]): String = xs.mkString(", ")
+  }
+}
+
+trait Serializer_1 extends Serializer_2 {
+  implicit val intSerializer: Serializer[Int] =  { t => "int" }
+  implicit val strSerializer: Serializer[String] = { t => "string" }
+  implicit val doubleSerializer: Serializer[Double] = { t => "double" }
+  implicit def listSerializer[T: Serializer]: Serializer[List[T]] = { ts =>
+    println(ts)
+    s"List[${ts.map { t => implicitly[Serializer[T]].serialize(t) }.mkString("-")}]"
+  }
+}
+
+trait Serializer_2 {
+  implicit def generic[T]: Serializer[T] = macro Macros.magnolia[T, Serializer[_]]
+}
-- 
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