Implement JsonWriter for Either

modules/core/src/main/scala/tethys/writers/instances/AllJsonWriters.scala

@@ -3,7 +3,7 @@ package tethys.writers.instances
 import tethys.JsonWriter
 import tethys.writers.tokens.TokenWriter
 
-trait AllJsonWriters extends OptionWriters {
+trait AllJsonWriters extends OptionWriters with EitherWriters {
   implicit lazy val intWriter: JsonWriter[Int] = new JsonWriter[Int] {
     override def write(value: Int, tokenWriter: TokenWriter): Unit = tokenWriter.writeNumber(value)
   }

modules/core/src/main/scala/tethys/writers/instances/EitherWriters.scala

@@ -0,0 +1,22 @@
+package tethys.writers.instances
+
+import tethys.JsonWriter
+import tethys.writers.tokens.TokenWriter
+
+private[tethys] trait EitherWriters {
+  implicit def eitherWriter[L, R](implicit L: JsonWriter[L], R: JsonWriter[R]): JsonWriter[Either[L, R]] = new JsonWriter[Either[L, R]] {
+    override def write(name: String, value: Either[L, R], tokenWriter: TokenWriter): Unit = {
+      value match {
+        case Left(left)   => L.write(name, left, tokenWriter)
+        case Right(right) => R.write(name, right, tokenWriter)
+      }
+    }
+
+    def write(value: Either[L, R], tokenWriter: TokenWriter): Unit = {
+      value match {
+        case Left(left)   => L.write(left, tokenWriter)
+        case Right(right) => R.write(right, tokenWriter)
+      }
+    }
+  }
+}

modules/core/src/test/scala/tethys/writers/DefaultWritersTest.scala

@@ -36,6 +36,8 @@ class DefaultWritersTest extends AnyFlatSpec {
     test(Map("a" -> 1, "b" -> 2)) -> obj("a" -> 1, "b" -> 2),
     test(Option(1), "Option.nonEmpty") -> value(1),
     test(Option.empty[Int], "Option.empty") -> List(NullValueNode),
+    test(Right(1): Either[String, Int], "Either.right") -> value(1),
+    test(Left("Not an Int"): Either[String, Int], "Either.left") -> value("Not an Int"),
     test(1: java.lang.Integer) -> value(1),
     test(java.lang.Short.valueOf(1: Short)) -> value(1: Short),
     test(1L: java.lang.Long) -> value(1L),