Add flatMap{Both,Either}

kotlin-result/src/commonMain/kotlin/com/github/michaelbull/result/Map.kt

@@ -22,6 +22,151 @@ public inline infix fun <V, E, U> Result<V, E>.map(transform: (V) -> U): Result<
     }
 }
 
+/**
+ * Maps this [Result<Result<V, E>, E>][Result] to [Result<V, E>][Result].
+ *
+ * - Rust: [Result.flatten](https://doc.rust-lang.org/std/result/enum.Result.html#method.flatten)
+ */
+public inline fun <V, E> Result<Result<V, E>, E>.flatten(): Result<V, E> {
+    return when (this) {
+        is Ok -> value
+        is Err -> this
+    }
+}
+
+/**
+ * Maps this [Result<V, E>][Result] to [Result<U, E>][Result] by either applying the [transform]
+ * function if this [Result] is [Ok], or returning this [Err].
+ *
+ * This is functionally equivalent to [andThen].
+ *
+ * - Scala: [Either.flatMap](http://www.scala-lang.org/api/2.12.0/scala/util/Either.html#flatMap[AA>:A,Y](f:B=>scala.util.Either[AA,Y]):scala.util.Either[AA,Y])
+ */
+public inline infix fun <V, E, U> Result<V, E>.flatMap(transform: (V) -> Result<U, E>): Result<U, E> {
+    contract {
+        callsInPlace(transform, InvocationKind.AT_MOST_ONCE)
+    }
+
+    return andThen(transform)
+}
+
+/**
+ * Maps this [Result<V, E>][Result] to [U] by applying either the [success] function if this
+ * [Result] is [Ok], or the [failure] function if this [Result] is an [Err].
+ *
+ * Unlike [mapEither], [success] and [failure] must both return [U].
+ *
+ * - Elm: [Result.Extra.mapBoth](http://package.elm-lang.org/packages/elm-community/result-extra/2.2.0/Result-Extra#mapBoth)
+ * - Haskell: [Data.Either.either](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Either.html#v:either)
+ */
+public inline fun <V, E, U> Result<V, E>.mapBoth(
+    success: (V) -> U,
+    failure: (E) -> U,
+): U {
+    contract {
+        callsInPlace(success, InvocationKind.AT_MOST_ONCE)
+        callsInPlace(failure, InvocationKind.AT_MOST_ONCE)
+    }
+
+    return when (this) {
+        is Ok -> success(value)
+        is Err -> failure(error)
+    }
+}
+
+/**
+ * Maps this [Result<V, E>][Result] to [U] by applying either the [success] function if this
+ * [Result] is [Ok], or the [failure] function if this [Result] is an [Err].
+ *
+ * Unlike [mapEither], [success] and [failure] must both return [U].
+ *
+ * This is functionally equivalent to [mapBoth].
+ *
+ * - Elm: [Result.Extra.mapBoth](http://package.elm-lang.org/packages/elm-community/result-extra/2.2.0/Result-Extra#mapBoth)
+ * - Haskell: [Data.Either.either](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Either.html#v:either)
+ */
+public inline fun <V, E, U> Result<V, E>.fold(
+    success: (V) -> U,
+    failure: (E) -> U,
+): U {
+    contract {
+        callsInPlace(success, InvocationKind.AT_MOST_ONCE)
+        callsInPlace(failure, InvocationKind.AT_MOST_ONCE)
+    }
+
+    return mapBoth(success, failure)
+}
+
+/**
+ * Maps this [Result<V, E>][Result] to [Result<U, E>][Result] by applying either the [success]
+ * function if this [Result] is [Ok], or the [failure] function if this [Result] is an [Err].
+ *
+ * Unlike [mapEither], [success] and [failure] must both return [U].
+ *
+ * - Elm: [Result.Extra.mapBoth](http://package.elm-lang.org/packages/elm-community/result-extra/2.2.0/Result-Extra#mapBoth)
+ * - Haskell: [Data.Either.either](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Either.html#v:either)
+ */
+public inline fun <V, E, U> Result<V, E>.flatMapBoth(
+    success: (V) -> Result<U, E>,
+    failure: (E) -> Result<U, E>,
+): Result<U, E> {
+    contract {
+        callsInPlace(success, InvocationKind.AT_MOST_ONCE)
+        callsInPlace(failure, InvocationKind.AT_MOST_ONCE)
+    }
+
+    return when (this) {
+        is Ok -> success(value)
+        is Err -> failure(error)
+    }
+}
+
+/**
+ * Maps this [Result<V, E>][Result] to [Result<U, F>][Result] by applying either the [success]
+ * function if this [Result] is [Ok], or the [failure] function if this [Result] is an [Err].
+ *
+ * Unlike [mapBoth], [success] and [failure] may either return [U] or [F] respectively.
+ *
+ * - Haskell: [Data.Bifunctor.Bimap](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Bifunctor.html#v:bimap)
+ */
+public inline fun <V, E, U, F> Result<V, E>.mapEither(
+    success: (V) -> U,
+    failure: (E) -> F,
+): Result<U, F> {
+    contract {
+        callsInPlace(success, InvocationKind.AT_MOST_ONCE)
+        callsInPlace(failure, InvocationKind.AT_MOST_ONCE)
+    }
+
+    return when (this) {
+        is Ok -> Ok(success(value))
+        is Err -> Err(failure(error))
+    }
+}
+
+/**
+ * Maps this [Result<V, E>][Result] to [Result<U, F>][Result] by applying either the [success]
+ * function if this [Result] is [Ok], or the [failure] function if this [Result] is an [Err].
+ *
+ * Unlike [mapBoth], [success] and [failure] may either return [U] or [F] respectively.
+ *
+ * - Haskell: [Data.Bifunctor.Bimap](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Bifunctor.html#v:bimap)
+ */
+public inline fun <V, E, U, F> Result<V, E>.flatMapEither(
+    success: (V) -> Result<U, F>,
+    failure: (E) -> Result<U, F>,
+): Result<U, F> {
+    contract {
+        callsInPlace(success, InvocationKind.AT_MOST_ONCE)
+        callsInPlace(failure, InvocationKind.AT_MOST_ONCE)
+    }
+
+    return when (this) {
+        is Ok -> success(value)
+        is Err -> failure(error)
+    }
+}
+
 /**
  * Maps this [Result<V, E>][Result] to [Result<V, F>][Result] by either applying the [transform]
  * function to the [error][Err.error] if this [Result] is [Err], or returning this [Ok].
@@ -94,88 +239,6 @@ public inline infix fun <V, E, U> Result<Iterable<V>, E>.mapAll(transform: (V) -
     }
 }
 
-/**
- * Maps this [Result<V, E>][Result] to [U] by applying either the [success] function if this
- * [Result] is [Ok], or the [failure] function if this [Result] is an [Err]. Both of these
- * functions must return the same type ([U]).
- *
- * - Elm: [Result.Extra.mapBoth](http://package.elm-lang.org/packages/elm-community/result-extra/2.2.0/Result-Extra#mapBoth)
- * - Haskell: [Data.Either.either](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Either.html#v:either)
- */
-public inline fun <V, E, U> Result<V, E>.mapBoth(success: (V) -> U, failure: (E) -> U): U {
-    contract {
-        callsInPlace(success, InvocationKind.AT_MOST_ONCE)
-        callsInPlace(failure, InvocationKind.AT_MOST_ONCE)
-    }
-
-    return when (this) {
-        is Ok -> success(value)
-        is Err -> failure(error)
-    }
-}
-
-/**
- * Maps this [Result<V, E>][Result] to [U] by applying either the [success] function if this
- * [Result] is [Ok], or the [failure] function if this [Result] is an [Err]. Both of these
- * functions must return the same type ([U]).
- *
- * This is functionally equivalent to [mapBoth].
- *
- * - Elm: [Result.Extra.mapBoth](http://package.elm-lang.org/packages/elm-community/result-extra/2.2.0/Result-Extra#mapBoth)
- * - Haskell: [Data.Either.either](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Either.html#v:either)
- */
-public inline fun <V, E, U> Result<V, E>.fold(success: (V) -> U, failure: (E) -> U): U {
-    contract {
-        callsInPlace(success, InvocationKind.AT_MOST_ONCE)
-        callsInPlace(failure, InvocationKind.AT_MOST_ONCE)
-    }
-
-    return mapBoth(success, failure)
-}
-
-/**
- * Maps this [Result<V, E>][Result] to [Result<U, F>][Result] by applying either the [success]
- * function if this [Result] is [Ok], or the [failure] function if this [Result] is an [Err].
- *
- * - Haskell: [Data.Bifunctor.Bimap](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Bifunctor.html#v:bimap)
- */
-public inline fun <V, E, U, F> Result<V, E>.mapEither(success: (V) -> U, failure: (E) -> F): Result<U, F> {
-    contract {
-        callsInPlace(success, InvocationKind.AT_MOST_ONCE)
-        callsInPlace(failure, InvocationKind.AT_MOST_ONCE)
-    }
-
-    return when (this) {
-        is Ok -> Ok(success(value))
-        is Err -> Err(failure(error))
-    }
-}
-
-/**
- * Maps this [Result<V, E>][Result] to [Result<U, E>][Result] by either applying the [transform]
- * function if this [Result] is [Ok], or returning this [Err].
- *
- * This is functionally equivalent to [andThen].
- *
- * - Scala: [Either.flatMap](http://www.scala-lang.org/api/2.12.0/scala/util/Either.html#flatMap[AA>:A,Y](f:B=>scala.util.Either[AA,Y]):scala.util.Either[AA,Y])
- */
-public inline infix fun <V, E, U> Result<V, E>.flatMap(transform: (V) -> Result<U, E>): Result<U, E> {
-    contract {
-        callsInPlace(transform, InvocationKind.AT_MOST_ONCE)
-    }
-
-    return andThen(transform)
-}
-
-/**
- * Maps this [Result<Result<V, E>, E>][Result] to [Result<V, E>][Result].
- *
- * - Rust: [Result.flatten](https://doc.rust-lang.org/std/result/enum.Result.html#method.flatten)
- */
-public inline fun <V, E> Result<Result<V, E>, E>.flatten(): Result<V, E> {
-    return andThen { it }
-}
-
 /**
  * Returns the [transformation][transform] of the [value][Ok.value] if this [Result] is [Ok]
  * and satisfies the given [predicate], otherwise this [Result].
@@ -194,6 +257,7 @@ public inline fun <V, E> Result<V, E>.toErrorIf(predicate: (V) -> Boolean, trans
         } else {
             this
         }
+
         is Err -> this
     }
 }
@@ -215,6 +279,7 @@ public inline fun <V, E> Result<V?, E>.toErrorIfNull(error: () -> E): Result<V,
         } else {
             Ok(value)
         }
+
         is Err -> this
     }
 }
@@ -237,6 +302,7 @@ public inline fun <V, E> Result<V, E>.toErrorUnless(predicate: (V) -> Boolean, t
         } else {
             this
         }
+
         is Err -> this
     }
 }
@@ -258,6 +324,7 @@ public inline fun <V, E> Result<V, E>.toErrorUnlessNull(error: () -> E): Result<
         } else {
             Err(error())
         }
+
         is Err -> Err(error())
     }
 }

kotlin-result/src/commonTest/kotlin/com/github/michaelbull/result/MapTest.kt

@@ -3,175 +3,41 @@ package com.github.michaelbull.result
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertNull
-import kotlin.test.assertSame
 
 class MapTest {
-    private sealed class MapErr(val reason: String) {
+    private sealed interface MapErr {
-        object HelloError : MapErr("hello")
+        val reason: String
-        object WorldError : MapErr("world")
+
-        class CustomError(reason: String) : MapErr(reason)
+        data object HelloError : MapErr {
+            override val reason = "hello"
+        }
+
+        data object WorldError : MapErr {
+            override val reason = "world"
+        }
+
+        data class CustomError(override val reason: String) : MapErr
     }
 
     class Map {
+
         @Test
         fun returnsTransformedValueIfOk() {
-            assertEquals(
+            val value: Result<Int, MapErr> = Ok(10)
-                expected = 30,
-                actual = Ok(10).map { it + 20 }.get()
-            )
-        }
-
-        @Test
-        @Suppress("UNREACHABLE_CODE")
-        fun returnsErrorIfErr() {
-            val result = Err(MapErr.HelloError).map { "hello $it" }
-
-            result as Err
-
-            assertSame(
-                expected = MapErr.HelloError,
-                actual = result.error
-            )
-        }
-    }
-
-    class MapError {
-        @Test
-        fun returnsValueIfOk() {
-            val value = Ok(55).map { it + 15 }.mapError { MapErr.WorldError }.get()
 
             assertEquals(
-                expected = 70,
+                expected = Ok(30),
-                actual = value
+                actual = value.map { it + 20 }
             )
         }
 
         @Test
         fun returnsErrorIfErr() {
-            val result: Result<String, MapErr> = Ok("let")
+            val value: Result<Int, MapErr> = Err(MapErr.HelloError)
-                .map { "$it me" }
-                .andThen {
-                    when (it) {
-                        "let me" -> Err(MapErr.CustomError("$it $it"))
-                        else -> Ok("$it get")
-                    }
-                }
-                .mapError { MapErr.CustomError("${it.reason} get what i want") }
-
-            result as Err
 
             assertEquals(
-                expected = "let me let me get what i want",
+                expected = Err(MapErr.HelloError),
-                actual = result.error.reason
+                actual = value.map { "hello $it" }
-            )
-        }
-    }
-
-    class MapOr {
-        @Test
-        fun returnsTransformedValueIfOk() {
-            val value = Ok("foo").mapOr(42, String::length)
-
-            assertEquals(
-                expected = 3,
-                actual = value
-            )
-        }
-
-        @Test
-        fun returnsDefaultValueIfErr() {
-            val value = Err("bar").mapOr(42, String::length)
-
-            assertEquals(
-                expected = 42,
-                actual = value
-            )
-        }
-    }
-
-    class MapOrElse {
-        private val k = 21
-
-        @Test
-        fun returnsTransformedValueIfOk() {
-            val value = Ok("foo").mapOrElse({ k * 2 }, String::length)
-
-            assertEquals(
-                expected = 3,
-                actual = value
-            )
-        }
-
-        @Test
-        fun returnsDefaultValueIfErr() {
-            val value = Err("bar").mapOrElse({ k * 2 }, String::length)
-
-            assertEquals(
-                expected = 42,
-                actual = value
-            )
-        }
-    }
-
-    class MapBoth {
-        @Test
-        @Suppress("UNREACHABLE_CODE")
-        fun returnsTransformedValueIfOk() {
-            val value = Ok("there is").mapBoth(
-                success = { "$it a light" },
-                failure = { "$it that never" }
-            )
-
-            assertEquals(
-                expected = "there is a light",
-                actual = value
-            )
-        }
-
-        @Test
-        @Suppress("UNREACHABLE_CODE")
-        fun returnsTransformedErrorIfErr() {
-            val error = Err(MapErr.CustomError("this")).mapBoth(
-                success = { "$it charming" },
-                failure = { "${it.reason} man" }
-            )
-
-            assertEquals(
-                expected = "this man",
-                actual = error
-            )
-        }
-    }
-
-    class MapEither {
-        @Test
-        @Suppress("UNREACHABLE_CODE")
-        fun returnsTransformedValueIfOk() {
-            val result = Ok(500).mapEither(
-                success = { it + 500 },
-                failure = { MapErr.CustomError("$it") }
-            )
-
-            result as Ok
-
-            assertEquals(
-                expected = 1000,
-                actual = result.value
-            )
-        }
-
-        @Test
-        fun returnsTransformedErrorIfErr() {
-            val result = Err("the reckless").mapEither(
-                success = { "the wild youth" },
-                failure = { MapErr.CustomError("the truth") }
-            )
-
-            result as Err
-
-            assertEquals(
-                expected = "the truth",
-                actual = result.error.reason
             )
         }
     }
@@ -224,6 +90,208 @@ class MapTest {
         }
     }
 
+    class MapError {
+
+        @Test
+        fun returnsValueIfOk() {
+            val value: Result<Int, MapErr> = Ok(70)
+
+            assertEquals(
+                expected = Ok(70),
+                actual = value.mapError { MapErr.WorldError }
+            )
+        }
+
+        @Test
+        fun returnsErrorIfErr() {
+            val value: Result<Int, MapErr> = Err(MapErr.HelloError)
+
+            assertEquals(
+                expected = Err(MapErr.WorldError),
+                actual = value.mapError { MapErr.WorldError }
+            )
+        }
+    }
+
+    class MapOr {
+
+        @Test
+        fun returnsTransformedValueIfOk() {
+            val value: Result<String, String> = Ok("foo")
+
+            assertEquals(
+                expected = 3,
+                actual = value.mapOr(42, String::length)
+            )
+        }
+
+        @Test
+        fun returnsDefaultValueIfErr() {
+            val value: Result<String, String> = Err("foo")
+
+            assertEquals(
+                expected = 42,
+                actual = value.mapOr(42, String::length)
+            )
+        }
+    }
+
+    class MapOrElse {
+        private val k = 21
+
+        @Test
+        fun returnsTransformedValueIfOk() {
+            val value: Result<String, String> = Ok("foo")
+
+            assertEquals(
+                expected = 3,
+                actual = value.mapOrElse({ k * 2 }, String::length)
+            )
+        }
+
+        @Test
+        fun returnsDefaultValueIfErr() {
+            val value: Result<String, String> = Err("foo")
+
+            assertEquals(
+                expected = 42,
+                actual = value.mapOrElse({ k * 2 }, String::length)
+            )
+        }
+    }
+
+    class MapBoth {
+
+        @Test
+        fun returnsTransformedValueIfOk() {
+            val value: Result<Int, Long> = Ok(50)
+
+            val result: String = value.mapBoth(
+                success = { "good $it" },
+                failure = { "bad $it" }
+            )
+
+            assertEquals(
+                expected = "good 50",
+                actual = result
+            )
+        }
+
+        @Test
+        fun returnsTransformedErrorIfErr() {
+            val value: Result<Int, Long> = Err(20)
+
+            val result: String = value.mapBoth(
+                success = { "good $it" },
+                failure = { "bad $it" }
+            )
+
+            assertEquals(
+                expected = "bad 20",
+                actual = result
+            )
+        }
+    }
+
+    class FlatMapBoth {
+
+        @Test
+        fun returnsTransformedValueIfOk() {
+            val value: Result<Int, Long> = Ok(50)
+
+            val result: Result<String, Long> = value.flatMapBoth(
+                success = { Ok("good $it") },
+                failure = { Err(100L) }
+            )
+
+            assertEquals(
+                expected = Ok("good 50"),
+                actual = result
+            )
+        }
+
+        @Test
+        fun returnsTransformedErrorIfErr() {
+            val result: Result<Int, Long> = Err(25L)
+
+            val value: Result<String, Long> = result.flatMapBoth(
+                success = { Ok("good $it") },
+                failure = { Err(100L) }
+            )
+
+            assertEquals(
+                expected = Err(100L),
+                actual = value
+            )
+        }
+    }
+
+    class MapEither {
+
+        @Test
+        fun returnsTransformedValueIfOk() {
+            val value: Result<Int, MapErr.HelloError> = Ok(500)
+
+            val result: Result<Long, MapErr.CustomError> = value.mapEither(
+                success = { it + 500L },
+                failure = { MapErr.CustomError("$it") }
+            )
+
+            assertEquals(
+                expected = Ok(1000L),
+                actual = result
+            )
+        }
+
+        @Test
+        fun returnsTransformedErrorIfErr() {
+            val value: Result<Int, MapErr.HelloError> = Err(MapErr.HelloError)
+
+            val result: Result<Long, MapErr.CustomError> = value.mapEither(
+                success = { it + 500L },
+                failure = { MapErr.CustomError("bad") }
+            )
+
+            assertEquals(
+                expected = Err(MapErr.CustomError("bad")),
+                actual = result
+            )
+        }
+    }
+
+    class FlatMapEither {
+
+        @Test
+        fun returnsTransformedValueIfOk() {
+            val value: Result<Int, MapErr.HelloError> = Ok(500)
+
+            val result: Result<Long, MapErr.CustomError> = value.flatMapEither(
+                success = { Ok(it + 500L) },
+                failure = { Err(MapErr.CustomError("$it")) }
+            )
+
+            assertEquals(
+                expected = Ok(1000L),
+                actual = result
+            )
+        }
+
+        @Test
+        fun returnsTransformedErrorIfErr() {
+            val value: Result<Int, MapErr.HelloError> = Err(MapErr.HelloError)
+
+            val result: Result<Long, MapErr.CustomError> = value.flatMapEither(
+                success = { Ok(it + 500L) },
+                failure = { Err(MapErr.CustomError("bad")) }
+            )
+
+            assertEquals(
+                expected = Err(MapErr.CustomError("bad")),
+                actual = result
+            )
+        }
+    }
+
     class ToErrorIfNull {
 
         @Test