Merge thoughtbot/Bindings as a subtree of CombineViewModel

CONTRIBUTING.md

@@ -0,0 +1,31 @@
+# Contributing
+
+We love contributions from everyone.
+By participating in this project,
+you agree to abide by the thoughtbot [code of conduct][].
+
+  [code of conduct]: https://thoughtbot.com/open-source-code-of-conduct
+
+We expect everyone to follow the code of conduct
+anywhere in thoughtbot's project codebases,
+issue trackers, chatrooms, and mailing lists.
+
+## Contributing Code
+
+Reactive extensions are usually small and straightforward to implement,
+making them a great way to share useful utilities for others to use.
+
+We consider all kinds of changes. If you have an idea but you're not sure
+whether it's likely to be accepted, feel free to [open an issue][] first to
+discuss it.
+
+  [open an issue]: https://github.com/thoughtbot/CombineViewModel/issues
+
+First make your change, being sure to test that it compiles on all supported
+platforms.
+
+Push to your fork. Write a [good commit message][commit]. Submit a pull request.
+
+  [commit]: http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html
+
+Thank you for contributing!

Example/Sources/CounterViewController.swift

@@ -8,8 +8,6 @@ final class CounterViewController: UITableViewController, ViewModelObserver {
 
   @ViewModel private var counter: Counter
 
-  var subscriptions: Set<AnyCancellable> = []
-
   required init?(coder: NSCoder) {
     super.init(coder: coder)
 

Example/Sources/TasksViewController.swift

@@ -21,8 +21,6 @@ final class TasksViewController: UITableViewController, ViewModelObserver {
     .appendingPathComponent("tasks.json", isDirectory: false)
   @ViewModel private var taskList: TaskList
 
-  var subscriptions: Set<AnyCancellable> = []
-
   required init?(coder: NSCoder) {
     super.init(coder: coder)
 

LICENSE

@@ -0,0 +1,19 @@
+Copyright (c) 2019-20 thoughtbot, inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

Package.swift

@@ -7,13 +7,20 @@ let package = Package(
   platforms: [
     .iOS(.v13),
     .macOS(.v10_15),
+    .tvOS(.v13),
+    .watchOS(.v6),
   ],
   products: [
     .library(name: "CombineViewModel", targets: ["CombineViewModel"]),
+    .library(name: "Bindings", targets: ["Bindings"]),
+    .library(name: "UIKitBindings", targets: ["UIKitBindings"]),
   ],
   targets: [
-    .target(name: "CombineViewModel"),
-    .target(name: "ObjCTestSupport", path: "Tests/ObjCTestSupport"),
+    .target(name: "CombineViewModel", dependencies: ["Bindings"]),
+    .target(name: "Bindings"),
+    .target(name: "UIKitBindings", dependencies: ["Bindings"]),
+
     .testTarget(name: "CombineViewModelTests", dependencies: ["CombineViewModel", "ObjCTestSupport"]),
+    .target(name: "ObjCTestSupport", path: "Tests/ObjCTestSupport"),
   ]
 )

README.md

@@ -2,7 +2,13 @@
 
 An implementation of the Model-View-ViewModel (MVVM) pattern using Combine.
 
-## Example
+- [Getting Started](#getting-started)
+- [Installation](#installation)
+- [Bindings](#bindings)
+- [Contributing](#contributing)
+- [About](#about)
+
+## Getting Started
 
 ### Step 1: A view model is class that conforms to `ObservableObject`
 
@@ -41,25 +47,20 @@ import CombineViewModel
 import UIKit
 
 // (1) Conform your view controller to the ViewModelObserver protocol.
-//
 final class CounterViewController: UIViewController, ViewModelObserver {
   @IBOutlet private var valueLabel: UILabel!
 
   // (2) Declare your view model using the `@ViewModel` property wrapper.
-  //
   @ViewModel private var counter: Counter
-  var subscriptions: Set<AnyCancellable> = []
 
   // (3) Initialize your view model in init().
-  //
   required init?(coder: NSCoder) {
     super.init(coder: coder)
     self.counter = Counter()
   }
 
   // (4) The `updateView()` method is automatically called on the main queue
   //     when the view model changes. It is always called after `viewDidLoad()`.
-  //
   func updateView() {
     valueLabel.text = counter.formattedValue
   }
@@ -73,3 +74,58 @@ final class CounterViewController: UIViewController, ViewModelObserver {
   }
 }
 ```
+
+## Installation
+
+CombineViewModel is distributed via Swift Package Manager. To add it to your
+Xcode project, navigate to File > Add Package Dependency…, paste in the
+repository URL, and follow the prompts.
+
+<img alt="Screen capture of Xcode on macOS Big Sur, with the Add Package Dependency menu item highlighted" width="945" src="/Documentation/Images/add-package-dependency.png">
+
+## Bindings
+
+CombineViewModel also provides the complementary [`Bindings`](/Sources/Bindings)
+module. It provides two operators — `<~`, the **input binding operator**, and
+`~>`, the **output binding operator** — along with various types and protocols
+that support it. Note that the concept of a "binding" provided by the Bindings
+module is different to [SwiftUI's `Binding` type][Binding].
+
+  [Binding]: https://developer.apple.com/documentation/swiftui/binding
+
+Platform-specific binding helpers are also provided:
+
+- [UIKitBindings](/Sources/UIKitBindings)
+
+## Contributing
+
+Have a useful reactive extension in your project?
+Please consider contributing it back to the community!
+
+For more details, see the [CONTRIBUTING][] document.
+Thank you, [contributors][]!
+
+  [CONTRIBUTING]: CONTRIBUTING.md
+  [contributors]: https://github.com/thoughtbot/Bindings/graphs/contributors
+
+## License
+
+CombineViewModel is Copyright © 2019–20 thoughtbot, inc.
+It is free software, and may be redistributed
+under the terms specified in the [LICENSE][] file.
+
+  [LICENSE]: /LICENSE
+
+## About
+
+![thoughtbot](http://presskit.thoughtbot.com/images/thoughtbot-logo-for-readmes.svg)
+
+Bindings is maintained and funded by thoughtbot, inc.
+The names and logos for thoughtbot are trademarks of thoughtbot, inc.
+
+We love open source software!
+See [our other projects][community]
+or [hire us][hire] to help build your product.
+
+  [community]: https://thoughtbot.com/community?utm_source=github
+  [hire]: https://thoughtbot.com/hire-us?utm_source=github

Sources/Bindings/BindingOwner.swift

@@ -0,0 +1,69 @@
+import Combine
+import Foundation
+
+private var bindingOwnerSubscriptionsKey: UInt8 = 0
+
+public protocol BindingOwner: AnyObject, ReactiveExtensionProvider {
+  associatedtype Subscriptions: Collection & ExpressibleByArrayLiteral = Set<AnyCancellable>
+    where Subscriptions.Element == AnyCancellable
+
+  var subscriptions: Subscriptions { get set }
+  func store<C: Cancellable>(_ subcription: C)
+}
+
+extension NSObject: BindingOwner {}
+
+extension BindingOwner where Subscriptions: RangeReplaceableCollection {
+  @inlinable
+  public var subscriptions: Subscriptions {
+    _read { yield _subscriptions }
+    set { _subscriptions = newValue }
+    _modify { yield &_subscriptions }
+  }
+
+  @inlinable
+  public func store<C: Cancellable>(_ subscription: C) {
+    subscription.store(in: &subscriptions)
+  }
+}
+
+extension BindingOwner where Subscriptions == Set<AnyCancellable> {
+  @inlinable
+  public var subscriptions: Subscriptions {
+    _read { yield _subscriptions }
+    set { _subscriptions = newValue }
+    _modify { yield &_subscriptions }
+  }
+
+  @inlinable
+  public func store<C: Cancellable>(_ subscription: C) {
+    subscription.store(in: &subscriptions)
+  }
+}
+
+extension BindingOwner {
+  @usableFromInline
+  var _subscriptions: Subscriptions {
+    _read {
+      yield _getBox().value
+    }
+    set {
+      _getBox().value = newValue
+    }
+    _modify {
+      yield &_getBox().value
+    }
+  }
+
+  @usableFromInline
+  func _getBox() -> Box<Subscriptions> {
+    let box: Box<Subscriptions>
+    if let object = objc_getAssociatedObject(self, &bindingOwnerSubscriptionsKey) {
+      box = object as! Box<Subscriptions>
+    } else {
+      box = Box([])
+      objc_setAssociatedObject(self, &bindingOwnerSubscriptionsKey, box, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
+    }
+    return box
+  }
+}

Sources/Bindings/BindingSink.swift

@@ -0,0 +1,77 @@
+import Combine
+
+public final class BindingSink<Owner: BindingOwner, Input> {
+  public typealias Failure = Never
+
+  private(set) weak var owner: Owner?
+  private let receiveCompletion: (Owner, Subscribers.Completion<Failure>) -> Void
+  private let receiveValue: (Owner, Input) -> Void
+  private var subscription: Subscription?
+
+  public init(owner: Owner, receiveCompletion: @escaping (Owner, Subscribers.Completion<Failure>) -> Void = { _, _ in }, receiveValue: @escaping (Owner, Input) -> Void) {
+    self.owner = owner
+    self.receiveCompletion = receiveCompletion
+    self.receiveValue = receiveValue
+  }
+
+  private func withOwner(_ body: (Owner) -> Void) {
+    if let owner = owner {
+      body(owner)
+    } else {
+      cancel()
+    }
+  }
+}
+
+extension BindingSink where Input == Void {
+  public convenience init(owner: Owner, receiveCompletion: @escaping (Owner, Subscribers.Completion<Failure>) -> Void = { _, _ in }, receiveValue: @escaping (Owner) -> Void) {
+    self.init(owner: owner, receiveCompletion: receiveCompletion, receiveValue: { owner, _ in receiveValue(owner) })
+  }
+}
+
+extension BindingSink where Input == Never {
+  public convenience init(owner: Owner, receiveCompletion: @escaping (Owner, Subscribers.Completion<Failure>) -> Void) {
+    self.init(owner: owner, receiveCompletion: receiveCompletion, receiveValue: { _, _ in })
+  }
+}
+
+extension BindingSink: Subscriber {
+  public func receive(subscription: Subscription) {
+    if owner != nil {
+      subscription.request(.unlimited)
+      self.subscription = subscription
+    } else {
+      subscription.cancel()
+    }
+  }
+
+  public func receive(_ input: Input) -> Subscribers.Demand {
+    withOwner { receiveValue($0, input) }
+    return .max(1)
+  }
+
+  public func receive(completion: Subscribers.Completion<Failure>) {
+    withOwner { receiveCompletion($0, completion) }
+  }
+}
+
+extension BindingSink: Cancellable {
+  public func cancel() {
+    subscription?.cancel()
+    subscription = nil
+    owner = nil
+  }
+}
+
+extension BindingSink: BindingSubscriber {
+  @discardableResult
+  public static func <~ <P: Publisher> (sink: BindingSink, publisher: P) -> AnyCancellable
+    where P.Output == Input, P.Failure == Failure
+  {
+    guard let owner = sink.owner else { return AnyCancellable({}) }
+    let cancellable = AnyCancellable(sink)
+    owner.store(cancellable)
+    publisher.subscribe(sink)
+    return cancellable
+  }
+}

Sources/Bindings/BindingSubscriber.swift

@@ -0,0 +1,38 @@
+import Combine
+
+infix operator <~: DefaultPrecedence
+
+public protocol BindingSubscriber: Subscriber, Cancellable {
+  @discardableResult
+  static func <~ <P: Publisher> (subscriber: Self, source: P) -> AnyCancellable
+    where P.Output == Input, P.Failure == Failure
+}
+
+extension Publisher {
+  @discardableResult
+  public static func ~> <B: BindingSubscriber> (source: Self, subscriber: B) -> AnyCancellable
+    where Output == B.Input, Failure == B.Failure
+  {
+    subscriber <~ source
+  }
+}
+
+// MARK: Optional
+
+extension BindingSubscriber {
+  @discardableResult
+  public static func <~ <P: Publisher> (subscriber: Self, source: P) -> AnyCancellable
+    where Input == P.Output?, Failure == P.Failure
+  {
+    subscriber <~ source.map(Optional.some)
+  }
+}
+
+extension Publisher {
+  @discardableResult
+  public static func ~> <B: BindingSubscriber> (source: Self, subscriber: B) -> AnyCancellable
+    where B.Input == Output?, B.Failure == Failure
+  {
+    subscriber <~ source
+  }
+}

Sources/Bindings/Box.swift

@@ -0,0 +1,8 @@
+@usableFromInline
+final class Box<T> {
+  var value: T
+
+  init(_ value: T) {
+    self.value = value
+  }
+}