Merge pull request #15 from drivergroup/symmetric-id-mapper

Allow explicit conversion with symmetric id mapper via apply

2 files changed, 14 insertions, 6 deletions

diff --git a/src/main/scala/xyz/driver/core/core.scala b/src/main/scala/xyz/driver/core/core.scala
index 1c92423..db2af95 100644
--- a/src/main/scala/xyz/driver/core/core.scala
+++ b/src/main/scala/xyz/driver/core/core.scala
@@ -39,12 +39,15 @@ package core {
     implicit def idEqual[T]: Equal[Id[T]]       = Equal.equal[Id[T]](_ == _)
     implicit def idOrdering[T]: Ordering[Id[T]] = Ordering.by[Id[T], String](_.value)
 
-    sealed trait Mapper[E, R]
+    sealed class Mapper[E, R] {
+      def apply[T >: E](id: Id[R]): Id[T]                                = Id[E](id.value)
+      def apply[T >: R](id: Id[E])(implicit dummy: DummyImplicit): Id[T] = Id[R](id.value)
+    }
     object Mapper {
-      def apply[E, R] = new Mapper[E, R] {}
+      def apply[E, R] = new Mapper[E, R]
     }
-    implicit def convertRE[R, E](id: Id[R])(implicit ev: Mapper[E, R]): Id[E] = Id[E](id.value)
-    implicit def convertER[E, R](id: Id[E])(implicit ev: Mapper[E, R]): Id[R] = Id[R](id.value)
+    implicit def convertRE[R, E](id: Id[R])(implicit mapper: Mapper[E, R]): Id[E] = mapper[E](id)
+    implicit def convertER[E, R](id: Id[E])(implicit mapper: Mapper[E, R]): Id[R] = mapper[R](id)
   }
 
   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 775fb27..08b1df2 100644
--- a/src/test/scala/xyz/driver/core/CoreTest.scala
+++ b/src/test/scala/xyz/driver/core/CoreTest.scala
@@ -47,15 +47,20 @@ class CoreTest extends FlatSpec with Matchers with MockitoSugar {
     implicit val xy = Id.Mapper[X, Y]
     implicit val yz = Id.Mapper[Y, Z]
 
-    // The real test is that the following statements compile:
+    // Test that implicit conversions work correctly
     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)
+
+    // Test that type inferrence for explicit conversions work correctly
+    val yid = y.id
+    val xid = xy(yid)
+    val zid = yz(yid)
+    (xid: Id[X]) should be(zid: Id[Z])
   }
 
   "Time" should "use TimeZone correctly when converting to Date" in {