Merge pull request #5 from myeonginwoo/fold

impl fold
myeonginwoo · Dec 28, 2016 · d616024 · d616024
2 parents ad9d607 + 6a85aaa
commit d616024
Show file tree

Hide file tree

Showing 2 changed files with 21 additions and 6 deletions.
diff --git a/Either/src/main/kotlin/Either.kt b/Either/src/main/kotlin/Either.kt
@@ -11,17 +11,24 @@ sealed class Either<L, R> {
     var left: LeftProjection<L, Nothing>? = null
     var right: RightProjection<Nothing, R>? = null
 
-    class Left<L, R>(value: L) : Either<L, R>() {
+    class Left<L, R>(val value: L) : Either<L, R>() {
         init {
             isLeft = true
             left = LeftProjection(value)
         }
     }
 
-    class Right<L, R>(value: R) : Either<L, R>() {
+    class Right<L, R>(val value: R) : Either<L, R>() {
         init {
             isRight = true
             right = RightProjection(value)
         }
     }
+
+    fun <X> fold(fLeft: (L) -> X, fRight: (R) -> X): X {
+        return when (this) {
+            is Left -> fLeft(value)
+            is Right -> fRight(value)
+        }
+    }
 }
diff --git a/Either/src/test/kotlin/EitherTest.kt b/Either/src/test/kotlin/EitherTest.kt
@@ -12,10 +12,10 @@ import org.junit.Test
 class EitherTest {
 
     @Test fun leftTest() {
-        val eitherLeft: Either<String, Int> = Left("test")
-        assertEquals("test", eitherLeft.left?.get)
-        assertEquals(true, eitherLeft.isLeft)
-        assertEquals(false, eitherLeft.isRight)
+        val leftEither: Either<String, Int> = Left("test")
+        assertEquals("test", leftEither.left?.get)
+        assertEquals(true, leftEither.isLeft)
+        assertEquals(false, leftEither.isRight)
     }
 
     @Test fun rightTest() {
@@ -66,4 +66,12 @@ class EitherTest {
         assertEquals(either.right?.filter { it < 100 }, null)
         assertEquals(either.right?.filter { it < 100 } ?: -1, -1)
     }
+
+    @Test fun foldTest() {
+        val leftEither: Either<String, Int> = Left("test")
+        assertEquals(leftEither.fold({ "Left is $it" }, { it * 3 }), "Left is test")
+
+        val rightEither: Either<String, Int> = Right(6)
+        assertEquals(rightEither.fold({ "Left is $it" }, { it * 3 }), 18)
+    }
 }