pt6_UnionType

Author: mtumilowicz

Diff for: src/main/scala/workshop/pt6_UnionType.scala

@@ -0,0 +1,9 @@
+package workshop
+
+object pt6_UnionType {
+
+  type Not[P] = P => Nothing
+  infix type v[T, U] = Not[Not[T] & Not[U]]
+  infix type |∨|[T, U] = [X] =>> Not[Not[X]] <:< (T v U)
+
+}

Diff for: src/test/scala/workshop/pt6_UnionTypeSpec.scala

@@ -0,0 +1,43 @@
+package workshop
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+import workshop.pt6_UnionType.*
+
+class pt6_UnionTypeSpec extends AnyFlatSpec with Matchers  {
+
+  it should "types specified in union type are subtype of union type" in {
+    assertCompiles("summon[Not[Not[Int]] <:< (Int v String)]")
+    assertCompiles("summon[Not[Not[String]] <:< (Int v String)]")
+  }
+
+  it should "types not specified in union type are not part of union type" in {
+    assertDoesNotCompile("summon[Not[Not[Float]] <:< (Double v Int)]")
+    assertDoesNotCompile("summon[Not[Not[String]] <:< (Double v Int)]")
+  }
+
+  it should "verify union types using evidence at compile time" in {
+    def size[T](t: T)(using Not[Not[T]] <:< (Int v String)) =
+      t match {
+        case i: Int => i
+        case s: String => s.length
+      }
+
+    assertCompiles("size(1)")
+    assertCompiles("size(\"11\")")
+    assertDoesNotCompile("size(1.0)")
+  }
+
+  it should "verify union types using bounds at compile time" in {
+    def size[T: (Int |∨| String)](t: T) =
+      t match {
+        case i: Int => i
+        case s: String => s.length
+      }
+
+    assertCompiles("size(1)")
+    assertCompiles("size(\"11\")")
+    assertDoesNotCompile("size(1.0)")
+  }
+
+}