BindingTarget + Smart Key Paths.

Author: andersio

CHANGELOG.md

@@ -1,6 +1,8 @@
 # master
 *Please add new entries at the top.*
 
+1. In Swift 3.2 or later, you may create `BindingTarget` for a key path of a specific object. (#440, kudos to @andersio)
+
 1. In Swift 3.2 or later, you can use `map()` with the new Smart Key Paths. (#435, kudos to @sharplet)
 
 1. When composing `Signal` and `SignalProducer` of inhabitable types, e.g. `Never` or `NoError`, ReactiveSwift now warns about operators that are illogical to use, and traps at runtime when such operators attempt to instantiate an instance. (#429, kudos to @andersio)

Sources/UnidirectionalBinding.swift

@@ -148,4 +148,30 @@ public struct BindingTarget<Value>: BindingTargetProvider {
 		}
 		self.init(lifetime: lifetime, action: setter)
 	}
+
+	#if swift(>=3.2)
+	// `Lifetime` is required on these overloads. RAC would provide convenience overloads
+	// for these with `lifetime(of:)`.
+
+	/// Creates a binding target.
+	///
+	/// - parameters:
+	///   - lifetime: The expected lifetime of any bindings towards `self`.
+	///   - object: The object to consume values.
+	///   - keyPath: The key path of the object that consumes values.
+	public init<Object: AnyObject>(lifetime: Lifetime, object: Object, keyPath: ReferenceWritableKeyPath<Object, Value>) {
+		self.init(lifetime: lifetime) { [weak object] in object?[keyPath: keyPath] = $0 }
+	}
+
+	/// Creates a binding target which consumes values on the specified scheduler.
+	///
+	/// - parameters:
+	///   - scheduler: The scheduler on which the `setter` consumes the values.
+	///   - lifetime: The expected lifetime of any bindings towards `self`.
+	///   - object: The object to consume values.
+	///   - keyPath: The key path of the object that consumes values.
+	public init<Object: AnyObject>(on scheduler: Scheduler, lifetime: Lifetime, object: Object, keyPath: ReferenceWritableKeyPath<Object, Value>) {
+		self.init(on: scheduler, lifetime: lifetime) { [weak object] in object?[keyPath: keyPath] = $0 }
+	}
+	#endif
 }

Tests/ReactiveSwiftTests/UnidirectionalBindingSpec.swift

@@ -5,87 +5,135 @@ import Nimble
 import Quick
 @testable import ReactiveSwift
 
+private class Object {
+	var value: Int = 0
+}
+
 class UnidirectionalBindingSpec: QuickSpec {
 	override func spec() {
 		describe("BindingTarget") {
 			var token: Lifetime.Token!
 			var lifetime: Lifetime!
-			var target: BindingTarget<Int>!
-			var optionalTarget: BindingTarget<Int?>!
-			var value: Int?
 
 			beforeEach {
 				token = Lifetime.Token()
 				lifetime = Lifetime(token)
-				target = BindingTarget(lifetime: lifetime, action: { value = $0 })
-				optionalTarget = BindingTarget(lifetime: lifetime, action: { value = $0 })
-				value = nil
 			}
 
-			describe("non-optional target") {
-				it("should pass through the lifetime") {
-					expect(target.lifetime).to(beIdenticalTo(lifetime))
+			describe("closure binding target") {
+				var target: BindingTarget<Int>!
+				var optionalTarget: BindingTarget<Int?>!
+				var value: Int?
+
+				beforeEach {
+					target = BindingTarget(lifetime: lifetime, action: { value = $0 })
+					optionalTarget = BindingTarget(lifetime: lifetime, action: { value = $0 })
+					value = nil
 				}
 
-				it("should trigger the supplied setter") {
-					expect(value).to(beNil())
+				describe("non-optional target") {
+					it("should pass through the lifetime") {
+						expect(target.lifetime).to(beIdenticalTo(lifetime))
+					}
 
-					target.action(1)
-					expect(value) == 1
+					it("should trigger the supplied setter") {
+						expect(value).to(beNil())
+
+						target.action(1)
+						expect(value) == 1
+					}
+
+					it("should accept bindings from properties") {
+						expect(value).to(beNil())
+
+						let property = MutableProperty(1)
+						target <~ property
+						expect(value) == 1
+
+						property.value = 2
+						expect(value) == 2
+					}
 				}
 
-				it("should accept bindings from properties") {
-					expect(value).to(beNil())
+				describe("optional target") {
+					it("should pass through the lifetime") {
+						expect(optionalTarget.lifetime).to(beIdenticalTo(lifetime))
+					}
 
-					let property = MutableProperty(1)
-					target <~ property
-					expect(value) == 1
+					it("should trigger the supplied setter") {
+						expect(value).to(beNil())
 
-					property.value = 2
-					expect(value) == 2
+						optionalTarget.action(1)
+						expect(value) == 1
+					}
+
+					it("should accept bindings from properties") {
+						expect(value).to(beNil())
+
+						let property = MutableProperty(1)
+						optionalTarget <~ property
+						expect(value) == 1
+
+						property.value = 2
+						expect(value) == 2
+					}
 				}
 			}
 
-			describe("optional target") {
+			#if swift(>=3.2)
+			describe("key path binding target") {
+				var target: BindingTarget<Int>!
+				var object: Object!
+
+				beforeEach {
+					object = Object()
+					target = BindingTarget(lifetime: lifetime, object: object, keyPath: \.value)
+				}
+
 				it("should pass through the lifetime") {
-					expect(optionalTarget.lifetime).to(beIdenticalTo(lifetime))
+					expect(target.lifetime).to(beIdenticalTo(lifetime))
 				}
 
 				it("should trigger the supplied setter") {
-					expect(value).to(beNil())
+					expect(object.value) == 0
 
-					optionalTarget.action(1)
-					expect(value) == 1
+					target.action(1)
+					expect(object.value) == 1
 				}
 
 				it("should accept bindings from properties") {
-					expect(value).to(beNil())
+					expect(object.value) == 0
 
 					let property = MutableProperty(1)
-					optionalTarget <~ property
-					expect(value) == 1
+					target <~ property
+					expect(object.value) == 1
 
 					property.value = 2
-					expect(value) == 2
+					expect(object.value) == 2
 				}
 			}
+			#endif
 
 			it("should not deadlock on the same queue") {
-				target = BindingTarget(on: UIScheduler(),
-				                       lifetime: lifetime,
-				                       action: { value = $0 })
+				var value: Int?
+
+				let target = BindingTarget(on: UIScheduler(),
+				                           lifetime: lifetime,
+				                           action: { value = $0 })
 
 				let property = MutableProperty(1)
 				target <~ property
 				expect(value) == 1
 			}
 
 			it("should not deadlock on the main thread even if the context was switched to a different queue") {
+				var value: Int?
+
 				let queue = DispatchQueue(label: #file)
 
-				target = BindingTarget(on: UIScheduler(),
-				                       lifetime: lifetime,
-				                       action: { value = $0 })
+				let target = BindingTarget(on: UIScheduler(),
+				                           lifetime: lifetime,
+				                           action: { value = $0 })
 
 				let property = MutableProperty(1)
 
@@ -97,6 +145,8 @@ class UnidirectionalBindingSpec: QuickSpec {
 			}
 
 			it("should not deadlock even if the value is originated from the same queue indirectly") {
+				var value: Int?
+
 				let key = DispatchSpecificKey<Void>()
 				DispatchQueue.main.setSpecific(key: key, value: ())
 
@@ -107,9 +157,9 @@ class UnidirectionalBindingSpec: QuickSpec {
 					mainQueueCounter.modify { $0 += DispatchQueue.getSpecific(key: key) != nil ? 1 : 0 }
 				}
 
-				target = BindingTarget(on: UIScheduler(),
-				                       lifetime: lifetime,
-				                       action: setter)
+				let target = BindingTarget(on: UIScheduler(),
+				                           lifetime: lifetime,
+				                           action: setter)
 
 				let scheduler: QueueScheduler
 				if #available(OSX 10.10, *) {