Merge pull request #53 from travisbrown/topic/relax-type-eq-constraint

Relax type equality constraint to subtype
typelevel · Jan 30, 2016 · c2416db · c2416db
2 parents ae1e204 + 815b7a2
commit c2416db
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diff --git a/core/src/main/scala/simulacrum/typeclass.scala b/core/src/main/scala/simulacrum/typeclass.scala
@@ -199,7 +199,7 @@ class TypeClassMacros(val c: Context) {
               if (arg equalsStructure Ident(simpleArg)) {
                 (withRewrittenFirst, true)
               } else {
-                val typeEqualityType = tq"_root_.scala.Predef.=:=[${liftedTypeArg.name}, $arg]"
+                val typeEqualityType = tq"_root_.scala.Predef.<:<[${liftedTypeArg.name}, $arg]"
                 val equalityEvidence = ValDef(Modifiers(Flag.IMPLICIT), TermName(c.freshName("ev")), typeEqualityType, EmptyTree)
                 val updatedParamss = {
                   if (withRewrittenFirst.nonEmpty && withRewrittenFirst.last.head.mods.hasFlag(Flag.IMPLICIT))

diff --git a/core/src/test/scala/simulacrum/typeclass.scala b/core/src/test/scala/simulacrum/typeclass.scala
@@ -303,6 +303,22 @@ class TypeClassTest extends WordSpec with Matchers {
         import Foo.ops._
         Option(Option(1)).bar
       }
+
+      "supports type inference for syntax for operations where the instance type is constrained" in {
+        @typeclass trait Ap[F[_]] {
+          def ap[A, B](ff: F[A => B])(fa: F[A]): F[B]
+        }
+
+        object Ap {
+          implicit val apOption: Ap[Option] = new Ap[Option] {
+            def ap[A, B](ff: Option[A => B])(fa: Option[A]): Option[B] = ff.flatMap(fa.map)
+          }
+        }
+
+        import Ap.ops._
+        val ff: Option[Int => String] = Some(_.toString)
+        ff.ap(Some(0)) shouldBe Some("0")
+      }
     }
 
     "support annotated companions" in {