Add Mapping.constant

taig · Sep 26, 2023 · 41990ca · 41990ca
1 parent bec9d28
commit 41990ca
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Showing 2 changed files with 28 additions and 9 deletions.
diff --git a/modules/core/src/main/scala/io/taig/enumeration/ext/Mapping.scala b/modules/core/src/main/scala/io/taig/enumeration/ext/Mapping.scala
@@ -1,7 +1,9 @@
 package io.taig.enumeration.ext
 
-import cats.{Hash, Inject}
+import cats.{Eq, Hash, Inject}
 import cats.syntax.all.*
+
+import scala.annotation.targetName
 import scala.collection.immutable.IntMap
 
 abstract class Mapping[A, B] extends Inject[A, B]:
@@ -15,3 +17,12 @@ object Mapping:
     val lookup: IntMap[A] = values.map(a => (f(a).hash, a)).to(IntMap)
     override def inj: A => B = f
     override def prj: B => Option[A] = b => lookup.get(b.hash)
+
+  def constant[A <: B: ValueOf, B: Eq]: Mapping[A, B] = new Mapping[A, B]:
+    val a: A = valueOf[A]
+    override def values: List[A] = List(a)
+    override def inj: A => B = identity
+    override def prj: B => Option[A] = b => Option.when(b === a)(a)
+
+  @targetName("constantOf")
+  def constant[A: Eq](value: A & Singleton): Mapping[value.type, A] = constant[value.type, A]
diff --git a/modules/core/src/test/scala/io/taig/enumeration/ext/MappingTest.scala b/modules/core/src/test/scala/io/taig/enumeration/ext/MappingTest.scala
@@ -9,15 +9,23 @@ final class MappingTest extends FunSuite:
       case Cat
       case Dog
 
-    val injection: Mapping[Animal, String] = Mapping.enumeration:
+    val mapping: Mapping[Animal, String] = Mapping.enumeration:
       case Animal.Bird => "Bird"
       case Animal.Cat  => "Cat"
       case Animal.Dog  => "Dog"
 
-    assertEquals(obtained = injection.inj(Animal.Bird), expected = "Bird")
-    assertEquals(obtained = injection.inj(Animal.Cat), expected = "Cat")
-    assertEquals(obtained = injection.inj(Animal.Dog), expected = "Dog")
-    assertEquals(obtained = injection.prj("Bird"), expected = Some(Animal.Bird))
-    assertEquals(obtained = injection.prj("Cat"), expected = Some(Animal.Cat))
-    assertEquals(obtained = injection.prj("Dog"), expected = Some(Animal.Dog))
-    assertEquals(obtained = injection.prj("Whale"), expected = None)
+    assertEquals(obtained = mapping.inj(Animal.Bird), expected = "Bird")
+    assertEquals(obtained = mapping.inj(Animal.Cat), expected = "Cat")
+    assertEquals(obtained = mapping.inj(Animal.Dog), expected = "Dog")
+    assertEquals(obtained = mapping.prj("Bird"), expected = Some(Animal.Bird))
+    assertEquals(obtained = mapping.prj("Cat"), expected = Some(Animal.Cat))
+    assertEquals(obtained = mapping.prj("Dog"), expected = Some(Animal.Dog))
+    assertEquals(obtained = mapping.prj("Whale"), expected = None)
+
+  test("enumeration.constant"):
+    val mapping = Mapping.constant[String]("foobar")
+
+    assertEquals(obtained = mapping.inj("foobar"), expected = "foobar")
+    assertEquals(obtained = mapping.prj("foobar"): Option[String], expected = Some("foobar"))
+    assertEquals(obtained = mapping.prj("foo"): Option[String], expected = None)
+    assertEquals(obtained = mapping.prj("bar"): Option[String], expected = None)