Convert Result to an inline value class

Author: michaelbull

kotlin-result-coroutines/src/commonMain/kotlin/com/github/michaelbull/result/coroutines/CoroutineBinding.kt

@@ -1,8 +1,9 @@
 package com.github.michaelbull.result.coroutines
 
-import com.github.michaelbull.result.Err
 import com.github.michaelbull.result.Ok
 import com.github.michaelbull.result.Result
+import com.github.michaelbull.result.asErr
+import com.github.michaelbull.result.binding
 import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Job
@@ -12,13 +13,31 @@ import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlin.contracts.InvocationKind
 import kotlin.contracts.contract
-import kotlin.coroutines.CoroutineContext
 
 /**
- * Suspending variant of [binding][com.github.michaelbull.result.binding].
- * The suspendable [block] runs in a new [CoroutineScope], inheriting the parent [CoroutineContext].
- * This new scope is [cancelled][CoroutineScope.cancel] once a failing bind is encountered, eagerly cancelling all
- * child [jobs][Job].
+ * Calls the specified function [block] with [CoroutineBindingScope] as its receiver and returns
+ * its [Result].
+ *
+ * When inside a binding [block], the [bind][CoroutineBindingScope.bind] function is accessible on
+ * any [Result]. Calling the [bind][CoroutineBindingScope.bind] function will attempt to unwrap the
+ * [Result] and locally return its [value][Result.value].
+ *
+ * Unlike [binding], this function is designed for _concurrent decomposition_ of work. When any
+ * [bind][CoroutineBindingScope.bind] returns an error, the [CoroutineScope] will be
+ * [cancelled][Job.cancel], cancelling all the other children.
+ *
+ * This function returns as soon as the given [block] and all its child coroutines are completed.
+ *
+ * Example:
+ * ```
+ * suspend fun provideX(): Result<Int, ExampleErr> { ... }
+ * suspend fun provideY(): Result<Int, ExampleErr> { ... }
+ *
+ * val result: Result<Int, ExampleErr> = coroutineBinding {
+ *   val x = async { provideX().bind() }
+ *   val y = async { provideY().bind() }
+ *   x.await() + y.await()
+ * }
  */
 public suspend inline fun <V, E> coroutineBinding(crossinline block: suspend CoroutineBindingScope<E>.() -> V): Result<V, E> {
     contract {
@@ -55,11 +74,12 @@ internal class CoroutineBindingScopeImpl<E>(
     var result: Result<Nothing, E>? = null
 
     override suspend fun <V> Result<V, E>.bind(): V {
-        return when (this) {
-            is Ok -> value
-            is Err -> mutex.withLock {
+        return if (isOk) {
+            value
+        } else {
+            mutex.withLock {
                 if (result == null) {
-                    result = this
+                    result = this.asErr()
                     coroutineContext.cancel(BindCancellationException)
                 }
 

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

@@ -4,20 +4,20 @@ import kotlin.contracts.InvocationKind
 import kotlin.contracts.contract
 
 /**
- * Returns [result] if this [Result] is [Ok], otherwise this [Err].
+ * Returns [result] if this result [is ok][Result.isOk], otherwise [this].
  *
  * - Rust: [Result.and](https://doc.rust-lang.org/std/result/enum.Result.html#method.and)
  */
 public infix fun <V, E, U> Result<V, E>.and(result: Result<U, E>): Result<U, E> {
-    return when (this) {
-        is Ok -> result
-        is Err -> this
+    return when {
+        isOk -> result
+        else -> this.asErr()
     }
 }
 
 /**
  * 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].
+ * function if this result [is ok][Result.isOk], or returning [this].
  *
  * - Elm: [Result.andThen](http://package.elm-lang.org/packages/elm-lang/core/latest/Result#andThen)
  * - Rust: [Result.and_then](https://doc.rust-lang.org/std/result/enum.Result.html#method.and_then)
@@ -27,8 +27,8 @@ public inline infix fun <V, E, U> Result<V, E>.andThen(transform: (V) -> Result<
         callsInPlace(transform, InvocationKind.AT_MOST_ONCE)
     }
 
-    return when (this) {
-        is Ok -> transform(value)
-        is Err -> this
+    return when {
+        isOk -> transform(value)
+        else -> this.asErr()
     }
 }

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

@@ -4,11 +4,14 @@ import kotlin.contracts.InvocationKind
 import kotlin.contracts.contract
 
 /**
- * Calls the specified function [block] with [BindingScope] as its receiver and returns its [Result].
+ * Calls the specified function [block] with [BindingScope] as its receiver and returns its
+ * [Result].
  *
- * When inside a [binding] block, the [bind][BindingScope.bind] function is accessible on any [Result]. Calling the
- * [bind][BindingScope.bind] function will attempt to unwrap the [Result] and locally return its [value][Ok.value]. If
- * the [Result] is an [Err], the binding block will terminate with that bind and return that failed-to-bind [Err].
+ * When inside a binding [block], the [bind][BindingScope.bind] function is accessible on any
+ * [Result]. Calling the [bind][BindingScope.bind] function will attempt to unwrap the [Result]
+ * and locally return its [value][Result.value].
+ *
+ * If a [bind][BindingScope.bind] returns an error, the [block] will terminate immediately.
  *
  * Example:
  * ```
@@ -48,12 +51,11 @@ internal class BindingScopeImpl<E> : BindingScope<E> {
     var result: Result<Nothing, E>? = null
 
     override fun <V> Result<V, E>.bind(): V {
-        return when (this) {
-            is Ok -> value
-            is Err -> {
-                this@BindingScopeImpl.result = this
-                throw BindException
-            }
+        return if (isOk) {
+            value
+        } else {
+            result = this.asErr()
+            throw BindException
         }
     }
 }

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

@@ -4,75 +4,66 @@ import kotlin.contracts.InvocationKind
 import kotlin.contracts.contract
 
 /**
- * Returns the [value][Ok.value] if this [Result] is [Ok], otherwise `null`.
+ * Returns the [value][Result.value] if this result [is ok][Result.isOk], otherwise `null`.
  *
  * - Elm: [Result.toMaybe](http://package.elm-lang.org/packages/elm-lang/core/latest/Result#toMaybe)
  * - Rust: [Result.ok](https://doc.rust-lang.org/std/result/enum.Result.html#method.ok)
  */
 public fun <V, E> Result<V, E>.get(): V? {
-    contract {
-        returnsNotNull() implies (this@get is Ok<V>)
-        returns(null) implies (this@get is Err<E>)
-    }
-
-    return when (this) {
-        is Ok -> value
-        is Err -> null
+    return when {
+        isOk -> value
+        else -> null
     }
 }
 
 /**
- * Returns the [error][Err.error] if this [Result] is [Err], otherwise `null`.
+ * Returns the [error][Result.error] if this result [is an error][Result.isErr], otherwise `null`.
  *
  * - Rust: [Result.err](https://doc.rust-lang.org/std/result/enum.Result.html#method.err)
  */
 public fun <V, E> Result<V, E>.getError(): E? {
-    contract {
-        returns(null) implies (this@getError is Ok<V>)
-        returnsNotNull() implies (this@getError is Err<E>)
-    }
-
-    return when (this) {
-        is Ok -> null
-        is Err -> error
+    return when {
+        isErr -> error
+        else -> null
     }
 }
 
 /**
- * Returns the [value][Ok.value] if this [Result] is [Ok], otherwise [default].
+ * Returns the [value][Result.value] if this result [is ok][Result.isOk], otherwise [default].
  *
  * - Elm: [Result.withDefault](http://package.elm-lang.org/packages/elm-lang/core/latest/Result#withDefault)
  * - Haskell: [Result.fromLeft](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Either.html#v:fromLeft)
  * - Rust: [Result.unwrap_or](https://doc.rust-lang.org/std/result/enum.Result.html#method.unwrap_or)
  *
  * @param default The value to return if [Err].
- * @return The [value][Ok.value] if [Ok], otherwise [default].
+ * @return The [value][Result.value] if [Ok], otherwise [default].
  */
 public infix fun <V, E> Result<V, E>.getOr(default: V): V {
-    return when (this) {
-        is Ok -> value
-        is Err -> default
+    return when {
+        isOk -> value
+        else -> default
     }
 }
 
 /**
- * Returns the [error][Err.error] if this [Result] is [Err], otherwise [default].
+ * Returns the [error][Result.error] if this result [is an error][Result.isErr], otherwise
+ * [default].
  *
  * - Haskell: [Result.fromRight](https://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Either.html#v:fromRight)
  *
  * @param default The error to return if [Ok].
- * @return The [error][Err.error] if [Err], otherwise [default].
+ * @return The [error][Result.error] if [Err], otherwise [default].
  */
 public infix fun <V, E> Result<V, E>.getErrorOr(default: E): E {
-    return when (this) {
-        is Ok -> default
-        is Err -> error
+    return when {
+        isOk -> default
+        else -> error
     }
 }
 
 /**
- * Returns the [value][Ok.value] if this [Result] is [Ok], otherwise the
- * [transformation][transform] of the [error][Err.error].
+ * Returns the [value][Result.value] if this result [is ok][Result.isOk], otherwise the
+ * [transformation][transform] of the [error][Result.error].
  *
  * - Elm: [Result.extract](http://package.elm-lang.org/packages/elm-community/result-extra/2.2.0/Result-Extra#extract)
  * - Rust: [Result.unwrap_or_else](https://doc.rust-lang.org/src/core/result.rs.html#735-740)
@@ -82,69 +73,64 @@ public inline infix fun <V, E> Result<V, E>.getOrElse(transform: (E) -> V): V {
         callsInPlace(transform, InvocationKind.AT_MOST_ONCE)
     }
 
-    return when (this) {
-        is Ok -> value
-        is Err -> transform(error)
+    return when {
+        isOk -> value
+        else -> transform(error)
     }
 }
 
 /**
- * Returns the [error][Err.error] if this [Result] is [Err], otherwise the
- * [transformation][transform] of the [value][Ok.value].
+ * Returns the [error][Result.error] if this result [is an error][Result.isErr], otherwise the
+ * [transformation][transform] of the [value][Result.value].
  */
 public inline infix fun <V, E> Result<V, E>.getErrorOrElse(transform: (V) -> E): E {
     contract {
         callsInPlace(transform, InvocationKind.AT_MOST_ONCE)
     }
 
-    return when (this) {
-        is Ok -> transform(value)
-        is Err -> error
+    return when {
+        isErr -> error
+        else -> transform(value)
     }
 }
 
 /**
- * Returns the [value][Ok.value] if this [Result] is [Ok], otherwise throws the
- * [error][Err.error].
+ * Returns the [value][Result.value] if this result [is ok][Result.isOk], otherwise throws the
+ * [error][Result.error].
  *
  * This is functionally equivalent to [`getOrElse { throw it }`][getOrElse].
  */
 public fun <V, E : Throwable> Result<V, E>.getOrThrow(): V {
-    contract {
-        returns() implies (this@getOrThrow is Ok<V>)
-    }
-
-    return when (this) {
-        is Ok -> value
-        is Err -> throw error
+    return when {
+        isOk -> value
+        else -> throw error
     }
 }
 
 /**
- * Returns the [value][Ok.value] if this [Result] is [Ok], otherwise throws the
- * [transformation][transform] of the [error][Err.error] to a [Throwable].
+ * Returns the [value][Result.value] if this result [is ok][Result.isOk], otherwise throws the
+ * [transformation][transform] of the [error][Result.error] to a [Throwable].
  */
 public inline infix fun <V, E> Result<V, E>.getOrThrow(transform: (E) -> Throwable): V {
     contract {
-        returns() implies (this@getOrThrow is Ok<V>)
         callsInPlace(transform, InvocationKind.AT_MOST_ONCE)
     }
 
-    return when (this) {
-        is Ok -> value
-        is Err -> throw transform(error)
+    return when {
+        isOk -> value
+        else -> throw transform(error)
     }
 }
 
 /**
- * Merges this [Result<V, E>][Result] to [U], returning the [value][Ok.value] if this [Result] is [Ok], otherwise the
- * [error][Err.error].
+ * Merges this [Result<V, E>][Result] to [U], returning the [value][Result.value] if this result
+ * [is ok][Result.isOk], otherwise the [error][Result.error].
  *
  * - Scala: [MergeableEither.merge](https://www.scala-lang.org/api/2.12.0/scala/util/Either$$MergeableEither.html#merge:A)
  */
 public fun <V : U, E : U, U> Result<V, E>.merge(): U {
-    return when (this) {
-        is Ok -> value
-        is Err -> error
+    return when {
+        isOk -> value
+        else -> error
     }
 }