scalajs cross build

1 files changed, 41 insertions, 0 deletions

diff --git a/examples/shared/src/main/scala/eq.scala b/examples/shared/src/main/scala/eq.scala
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+++ b/examples/shared/src/main/scala/eq.scala
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+package magnolia.examples
+
+import magnolia._
+import scala.language.experimental.macros
+
+/** typeclass for testing the equality of two values of the same type */
+trait Eq[T] { def equal(value: T, value2: T): Boolean }
+
+/** companion object to [[Eq]] */
+object Eq {
+
+  /** type constructor for the equality typeclass */
+  type Typeclass[T] = Eq[T]
+
+  /** defines equality for this case class in terms of equality for all its parameters */
+  def combine[T](ctx: CaseClass[Eq, T]): Eq[T] = new Eq[T] {
+    def equal(value1: T, value2: T) = ctx.parameters.forall { param =>
+      param.typeclass.equal(param.dereference(value1), param.dereference(value2))
+    }
+  }
+
+  /** choose which equality subtype to defer to
+    *
+    *  Note that in addition to dispatching based on the type of the first parameter to the `equal`
+    *  method, we check that the second parameter is the same type. */
+  def dispatch[T](ctx: SealedTrait[Eq, T]): Eq[T] = new Eq[T] {
+    def equal(value1: T, value2: T): Boolean = ctx.dispatch(value1) {
+      case sub =>
+        sub.cast.isDefinedAt(value2) && sub.typeclass.equal(sub.cast(value1), sub.cast(value2))
+    }
+  }
+
+  /** equality typeclass instance for strings */
+  implicit val string: Eq[String] = new Eq[String] { def equal(v1: String, v2: String) = v1 == v2 }
+
+  /** equality typeclass instance for integers */
+  implicit val int: Eq[Int] = new Eq[Int] { def equal(v1: Int, v2: Int) = v1 == v2 }
+
+  /** binds the Magnolia macro to the `gen` method */
+  implicit def gen[T]: Eq[T] = macro Magnolia.gen[T]
+}