Merge pull request #11 from drivergroup/typesafe-id-no-eq-relation

Typesafe Id mapping via implicit conversions.

2 files changed, 25 insertions, 0 deletions

diff --git a/src/main/scala/xyz/driver/core/core.scala b/src/main/scala/xyz/driver/core/core.scala
index 8ae9122..783150a 100644
--- a/src/main/scala/xyz/driver/core/core.scala
+++ b/src/main/scala/xyz/driver/core/core.scala
@@ -32,6 +32,10 @@ package core {
   object Id {
     implicit def idEqual[T]: Equal[Id[T]]       = Equal.equal[Id[T]](_ == _)
     implicit def idOrdering[T]: Ordering[Id[T]] = Ordering.by[Id[T], String](_.value)
+
+    object Mapper {
+      def apply[A, B]: (Id[A] => Id[B]) = (id: Id[A]) => Id[B](id.value)
+    }
   }
 
   final case class Name[+Tag](value: String) extends AnyVal {
diff --git a/src/test/scala/xyz/driver/core/CoreTest.scala b/src/test/scala/xyz/driver/core/CoreTest.scala
index 3eb9eaa..da9fd9a 100644
--- a/src/test/scala/xyz/driver/core/CoreTest.scala
+++ b/src/test/scala/xyz/driver/core/CoreTest.scala
@@ -39,6 +39,27 @@ class CoreTest extends FlatSpec with Matchers with MockitoSugar {
     theSameElementsInOrderAs(Seq(Id[String]("1"), Id[String]("2"), Id[String]("3"), Id[String]("4")))
   }
 
+  it should "have type-safe conversions" in {
+    final case class X(id: Id[X])
+    final case class Y(id: Id[Y])
+    final case class Z(id: Id[Z])
+
+    implicit val xy = Id.Mapper[X, Y]
+    implicit val yx = Id.Mapper[Y, X]
+    implicit val yz = Id.Mapper[Y, Z]
+    implicit val zy = Id.Mapper[Z, Y]
+
+    // The real test is that the following statements compile:
+    val x  = X(Id("0"))
+    val y  = Y(x.id)
+    val z  = Z(y.id)
+    val y2 = Y(z.id)
+    val x2 = X(y2.id)
+
+    (x2 === x) should be(true)
+    (y2 === y) should be(true)
+  }
+
   "Name" should "have equality and ordering working correctly" in {
 
     (Name[String]("foo") === Name[String]("foo")) should be(true)