UUID instances

core/src/main/scala/cats/instances/all.scala

@@ -17,3 +17,4 @@ trait AllInstances
   with    FutureInstances
   with    TryInstances
   with    TupleInstances
+  with    UUIDInstances

core/src/main/scala/cats/instances/uuid.scala

@@ -0,0 +1,9 @@
+package cats
+package instances
+
+import java.util.UUID
+
+trait UUIDInstances extends cats.kernel.instances.UUIDInstances {
+  implicit val catsStdShowForUUID: Show[UUID] =
+    Show.fromToString[UUID]
+}

kernel-laws/src/test/scala/cats/kernel/laws/LawTests.scala

@@ -15,6 +15,8 @@ import org.scalatest.FunSuite
 import scala.util.Random
 import scala.collection.immutable.BitSet
 
+import java.util.UUID
+
 class LawTests extends FunSuite with Discipline {
 
   // The scalacheck defaults (100,100) are too high for scala-js.
@@ -33,6 +35,9 @@ class LawTests extends FunSuite with Discipline {
   implicit val arbitrarySymbol: Arbitrary[Symbol] =
     Arbitrary(arbitrary[String].map(s => Symbol(s)))
 
+  implicit val arbitraryUUID: Arbitrary[UUID] =
+    Arbitrary(Gen.uuid)
+
   // this instance is not available in scalacheck 1.13.2.
   // remove this once a newer version is available.
   implicit val cogenBigInt: Cogen[BigInt] =
@@ -46,6 +51,9 @@ class LawTests extends FunSuite with Discipline {
   implicit val cogenSymbol: Cogen[Symbol] =
     Cogen[String].contramap(_.name)
 
+  implicit val cogenUUID: Cogen[UUID] =
+    Cogen[(Long, Long)].contramap(u => (u.getMostSignificantBits, u.getLeastSignificantBits))
+
   {
     // needed for Cogen[Map[...]]
     implicit val ohe: Ordering[HasEq[Int]] = Ordering[Int].on(_.a)
@@ -78,6 +86,7 @@ class LawTests extends FunSuite with Discipline {
   laws[OrderLaws, Long].check(_.order)
   laws[OrderLaws, BitSet].check(_.partialOrder)
   laws[OrderLaws, BigInt].check(_.order)
+  laws[OrderLaws, UUID].check(_.order)
   laws[OrderLaws, List[Int]].check(_.order)
   laws[OrderLaws, Option[String]].check(_.order)
   laws[OrderLaws, List[String]].check(_.order)

kernel/src/main/scala/cats/kernel/Order.scala

@@ -203,4 +203,11 @@ object Order extends OrderFunctions[Order] {
 
       override def toOrdering: Ordering[A] = ev
     }
+
+  def fromComparable[A <: Comparable[A]]: Order[A] = {
+    new Order[A] {
+      override def compare(x: A, y: A): Int =
+        x compareTo y
+    }
+  }
 }

kernel/src/main/scala/cats/kernel/instances/all.scala

@@ -25,4 +25,5 @@ trait AllInstances
     with SymbolInstances
     with TupleInstances
     with UnitInstances
+    with UUIDInstances
     with VectorInstances

kernel/src/main/scala/cats/kernel/instances/uuid.scala

@@ -0,0 +1,11 @@
+package cats.kernel
+package instances
+
+import java.util.UUID
+
+package object uuid extends UUIDInstances
+
+trait UUIDInstances {
+  implicit val catsKernelStdOrderForUUID: Order[UUID] =
+    Order.fromComparable[UUID]
+}