Add the Empty[SortedMap[A, B]] instance in alleycats

Author: danicheg

alleycats-core/src/main/scala/alleycats/Empty.scala

@@ -24,6 +24,8 @@ package alleycats
 import cats.{Eq, Monoid}
 import cats.syntax.eq.*
 
+import scala.collection.immutable.SortedMap
+
 trait Empty[A] extends Serializable {
   def empty: A
 
@@ -84,6 +86,9 @@ private[alleycats] trait EmptyInstances0 extends compat.IterableEmptyInstance wi
 
   private[this] val emptyMapSingleton: Empty[Map[Nothing, Nothing]] = Empty(Map.empty)
   implicit def alleycatsEmptyForMap[A, B]: Empty[Map[A, B]] = emptyMapSingleton.asInstanceOf[Empty[Map[A, B]]]
+
+  implicit def alleycatsEmptyForSortedMap[A: Ordering, B]: Empty[SortedMap[A, B]] =
+    Empty(SortedMap.empty[A, B])
 }
 
 private[alleycats] trait EmptyInstances1 extends EmptyInstances2 {

alleycats-core/src/test/scala/alleycats/SyntaxSuite.scala

@@ -24,6 +24,8 @@ package alleycats
 import cats.{Eq, Foldable}
 import alleycats.syntax.all.{catsSyntaxExtract, EmptyOps, ExtraFoldableOps}
 
+import scala.collection.immutable.SortedMap
+
 /**
  * Test that our syntax implicits are working.
  *
@@ -70,6 +72,14 @@ object SyntaxSuite {
     val _ = Empty[Map[Foo[Int], Foo[String]]].empty
   }
 
+  def testSortedMapEmpty(): Any = {
+    case class Foo[A](foo: A)
+
+    implicit def fooOrd[A: Ordering]: Ordering[Foo[A]] = Ordering.by(_.foo)
+
+    val _ = Empty[SortedMap[Foo[Int], Foo[String]]].empty
+  }
+
   def testFoldable[F[_]: Foldable, A](): Unit = {
     val x = mock[F[A]]
     val y = mock[A => Unit]