Merge pull request #273 from bignerdranch/zwaldowski/back-result

 Backpedal on hoisting Task.Result out of Task

Sources/Task/ExistentialTask.swift

@@ -3,7 +3,7 @@
 //  Deferred
 //
 //  Created by Zachary Waldowski on 3/28/16.
-//  Copyright © 2015-2018 Big Nerd Ranch. Licensed under MIT.
+//  Copyright © 2015-2019 Big Nerd Ranch. Licensed under MIT.
 //
 
 import Dispatch
@@ -189,6 +189,15 @@ import Deferred.Atomics
 /// - seealso: `TaskProtocol`
 /// - seealso: `Future`
 public final class Task<SuccessValue>: NSObject {
+    /// A type that represents either a wrapped value or an error, representing the
+    /// possible return values of a throwing function.
+    public enum Result {
+        /// The success value, stored as `Value`.
+        case success(SuccessValue)
+        /// The failure value, stored as any error.
+        case failure(Error)
+    }
+
     private let future: Future<Result>
 
     #if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
@@ -246,9 +255,6 @@ public final class Task<SuccessValue>: NSObject {
 }
 
 extension Task: TaskProtocol {
-    /// A type for returning and propagating recoverable errors.
-    public typealias Result = TaskResult<SuccessValue>
-
     public func upon(_ executor: Executor, execute body: @escaping(Result) -> Void) {
         future.upon(executor, execute: body)
     }

Sources/Task/ResultRecovery.swift

@@ -3,16 +3,15 @@
 //  Deferred
 //
 //  Created by Zachary Waldowski on 12/9/15.
-//  Copyright © 2014-2018 Big Nerd Ranch. Licensed under MIT.
+//  Copyright © 2014-2019 Big Nerd Ranch. Licensed under MIT.
 //
 
-extension TaskResult {
+extension Task.Result {
     /// Evaluates the `transform` for a success result, passing its unwrapped
     /// value as the parameter, to derive a new value.
     ///
     /// Use the `map` method with a closure that produces a new value.
-    @_inlineable
-    public func map<NewValue>(_ transform: (Value) throws -> NewValue) -> TaskResult<NewValue> {
+    public func map<NewValue>(_ transform: (SuccessValue) throws -> NewValue) -> Task<NewValue>.Result {
         switch self {
         case .success(let value):
             do {
@@ -29,8 +28,7 @@ extension TaskResult {
     /// value as the parameter, to derive a new result.
     ///
     /// Use `flatMap` with a closure that itself returns a result.
-    @_inlineable
-    public func flatMap<NewValue>(_ transform: (Value) throws -> TaskResult<NewValue>) -> TaskResult<NewValue> {
+    public func flatMap<NewValue>(_ transform: (SuccessValue) throws -> Task<NewValue>.Result) -> Task<NewValue>.Result {
         switch self {
         case .success(let value):
             do {
@@ -43,24 +41,3 @@ extension TaskResult {
         }
     }
 }
-
-extension TaskResult {
-    /// Performs a coalescing operation, returning the result of unwrapping the
-    /// success value of `result`, or `defaultValue` in case of an error.
-    @_inlineable
-    public static func ?? (result: TaskResult<Value>, defaultValue: @autoclosure() throws -> Value) rethrows -> Value {
-        switch result {
-        case .success(let value):
-            return value
-        case .failure:
-            return try defaultValue()
-        }
-    }
-
-    /// Performs a coalescing operation, the wrapped success value `result`, or
-    /// that of `defaultValue` in case of an error.
-    @_inlineable
-    public static func ?? (result: TaskResult<Value>, defaultValue: @autoclosure() throws -> TaskResult<Value>) rethrows -> TaskResult<Value> {
-        return try result.withValues(ifLeft: { _ in try defaultValue() }, ifRight: TaskResult.success)
-    }
-}

Sources/Task/TaskResult.swift

@@ -3,24 +3,15 @@
 //  Deferred
 //
 //  Created by Zachary Waldowski on 12/9/15.
-//  Copyright © 2014-2018 Big Nerd Ranch. Licensed under MIT.
+//  Copyright © 2014-2019 Big Nerd Ranch. Licensed under MIT.
 //
 
-/// A type that represents either a wrapped value or an error, representing the
-/// possible return values of a throwing function.
-public enum TaskResult<Value> {
-    /// The success value, stored as `Value`.
-    case success(Value)
-    /// The failure value, stored as any error.
-    case failure(Error)
-}
-
 // MARK: - Initializers
 
-extension TaskResult {
+extension Task.Result {
     /// Creates an instance storing a successful `value`.
     @_inlineable
-    public init(success value: @autoclosure() throws -> Value) {
+    public init(success value: @autoclosure() throws -> SuccessValue) {
         self.init(from: value)
     }
 
@@ -32,7 +23,7 @@ extension TaskResult {
 
     /// Create an exclusive success/failure state derived from two optionals,
     /// in the style of Cocoa completion handlers.
-    public init(value: Value?, error: Error?) {
+    public init(value: SuccessValue?, error: Error?) {
         switch (value, error) {
         case (let value?, _):
             // Ignore error if value is non-nil
@@ -49,7 +40,7 @@ private enum TaskResultInitializerError: Error {
     case invalidInput
 }
 
-extension TaskResult where Value == Void {
+extension Task.Result where SuccessValue == Void {
     /// Creates the success value.
     @_inlineable
     public init() {
@@ -59,19 +50,19 @@ extension TaskResult where Value == Void {
 
 // MARK: - Compatibility with Protocol Extensions
 
-extension TaskResult: Either {
+extension Task.Result: Either {
     @_inlineable
     public init(left error: Error) {
         self = .failure(error)
     }
 
     @_inlineable
-    public init(right value: Value) {
+    public init(right value: SuccessValue) {
         self = .success(value)
     }
 
     @_inlineable
-    public func withValues<Return>(ifLeft left: (Error) throws -> Return, ifRight right: (Value) throws -> Return) rethrows -> Return {
+    public func withValues<Return>(ifLeft left: (Error) throws -> Return, ifRight right: (SuccessValue) throws -> Return) rethrows -> Return {
         switch self {
         case let .success(value):
             return try right(value)

Tests/TaskTests/TaskProgressTests.swift

@@ -3,7 +3,7 @@
 //  DeferredTests
 //
 //  Created by Zachary Waldowski on 10/11/18.
-//  Copyright © 2018 Big Nerd Ranch. Licensed under MIT.
+//  Copyright © 2018-2019 Big Nerd Ranch. Licensed under MIT.
 //
 
 import XCTest
@@ -122,7 +122,7 @@ class TaskProgressTests: CustomExecutorTestCase {
         ], timeout: shortTimeout)
     }
 
-    private func delaySuccessAsFuture<Value>(_ value: @autoclosure @escaping() -> Value) -> Future<TaskResult<Value>> {
+    private func delaySuccessAsFuture<Value>(_ value: @autoclosure @escaping() -> Value) -> Future<Task<Value>.Result> {
         let deferred = Task<Value>.Promise()
         afterShortDelay {
             deferred.succeed(with: value())

Tests/TaskTests/TaskProtocolTests.swift

@@ -3,7 +3,7 @@
 //  Deferred
 //
 //  Created by Zachary Waldowski on 9/26/18.
-//  Copyright © 2018 Big Nerd Ranch. Licensed under MIT.
+//  Copyright © 2018-2019 Big Nerd Ranch. Licensed under MIT.
 //
 
 import XCTest
@@ -19,7 +19,7 @@ class TaskProtocolTests: XCTestCase {
 
     func testConditionalFutureInitAmbiguity() {
         // This is a compiler-time check only.
-        typealias Result = TaskResult<Int>
+        typealias Result = Task<Int>.Result
         let deferred = Deferred<Result>()
         _ = Future(deferred)
     }

Tests/TaskTests/TaskResultTests.swift

@@ -3,7 +3,7 @@
 //  DeferredTests
 //
 //  Created by Zachary Waldowski on 2/7/15.
-//  Copyright © 2014-2018 Big Nerd Ranch. Licensed under MIT.
+//  Copyright © 2014-2019 Big Nerd Ranch. Licensed under MIT.
 //
 
 import XCTest
@@ -23,10 +23,6 @@ class TaskResultTests: XCTestCase {
         ("testDebugDescriptionFailure", testDebugDescriptionFailure),
         ("testSuccessExtract", testSuccessExtract),
         ("testFailureExtract", testFailureExtract),
-        ("testCoalesceSuccessValue", testCoalesceSuccessValue),
-        ("testCoalesceFailureValue", testCoalesceFailureValue),
-        ("testFlatCoalesceSuccess", testFlatCoalesceSuccess),
-        ("testFlatCoalesceSuccess", testFlatCoalesceSuccess),
         ("testInitializeWithBlockSuccess", testInitializeWithBlockSuccess),
         ("testInitializeWithBlockError", testInitializeWithBlockError),
         ("testInitializeWithBlockInitFailure", testInitializeWithBlockInitFailure)
@@ -47,12 +43,12 @@ class TaskResultTests: XCTestCase {
 
     func testDebugDescriptionSuccess() {
         let debugDescription = String(reflecting: aSuccessResult)
-        XCTAssert(debugDescription.hasSuffix("TaskResult<Swift.Int>.success(42)"))
+        XCTAssert(debugDescription.hasSuffix("Task<Swift.Int>.Result.success(42)"))
     }
 
     func testDebugDescriptionFailure() {
         let debugDescription = String(reflecting: aFailureResult)
-        XCTAssert(debugDescription.hasSuffix("TaskResult<Swift.Int>.failure(TestError.first)"))
+        XCTAssert(debugDescription.hasSuffix("Task<Swift.Int>.Result.failure(TestError.first)"))
     }
 
     func testSuccessExtract() {
@@ -63,24 +59,6 @@ class TaskResultTests: XCTestCase {
         XCTAssertThrowsError(try aFailureResult.extract())
     }
 
-    func testCoalesceSuccessValue() {
-        XCTAssertEqual(aSuccessResult ?? 43, 42)
-    }
-
-    func testCoalesceFailureValue() {
-        XCTAssertEqual(aFailureResult ?? 43, 43)
-    }
-
-    func testFlatCoalesceSuccess() {
-        let result = aSuccessResult ?? Result.success(84)
-        XCTAssertEqual(try result.extract(), 42)
-    }
-
-    func testFlatCoalesceFailure() {
-        let result = aFailureResult ?? Result(success: 84)
-        XCTAssertEqual(try result.extract(), 84)
-    }
-
     func testInitializeWithBlockSuccess() {
         let result = Result(value: 42, error: nil)
         XCTAssertEqual(try result.extract(), 42)

Tests/TaskTests/VoidResultTests.swift

@@ -38,12 +38,12 @@ class VoidResultTests: XCTestCase {
 
     func testDebugDescriptionSuccess() {
         let debugDescription = String(reflecting: aSuccessResult)
-        XCTAssert(debugDescription.hasSuffix("TaskResult<()>.success()"))
+        XCTAssert(debugDescription.hasSuffix("Task<()>.Result.success()"))
     }
 
     func testDebugDescriptionFailure() {
         let debugDescription = String(reflecting: aFailureResult)
-        XCTAssert(debugDescription.hasSuffix("TaskResult<()>.failure(TestError.first)"))
+        XCTAssert(debugDescription.hasSuffix("Task<()>.Result.failure(TestError.first)"))
     }
 
     func testExtract() {