Merge pull request ReactiveCocoa#3131 from ReactiveCocoa/property-lifetime

Introduce the `BindingTarget` protocol.

Author: mdiep

ReactiveCocoa.xcodeproj/project.pbxproj

@@ -243,6 +243,10 @@
 		9A1E72BA1D4DE96500CC20C3 /* KeyValueObservingSpec.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A1E72B91D4DE96500CC20C3 /* KeyValueObservingSpec.swift */; };
 		9A1E72BB1D4DE96500CC20C3 /* KeyValueObservingSpec.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A1E72B91D4DE96500CC20C3 /* KeyValueObservingSpec.swift */; };
 		9A1E72BC1D4DE96500CC20C3 /* KeyValueObservingSpec.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A1E72B91D4DE96500CC20C3 /* KeyValueObservingSpec.swift */; };
+		9A694EF31D5CE02E009B05BD /* UnidirectionalBinding.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A694EF21D5CE02E009B05BD /* UnidirectionalBinding.swift */; };
+		9A694EF41D5CE02E009B05BD /* UnidirectionalBinding.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A694EF21D5CE02E009B05BD /* UnidirectionalBinding.swift */; };
+		9A694EF51D5CE02E009B05BD /* UnidirectionalBinding.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A694EF21D5CE02E009B05BD /* UnidirectionalBinding.swift */; };
+		9A694EF61D5CE02E009B05BD /* UnidirectionalBinding.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A694EF21D5CE02E009B05BD /* UnidirectionalBinding.swift */; };
 		9ABCB1851D2A5B5A00BCA243 /* Deprecations+Removals.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9ABCB1841D2A5B5A00BCA243 /* Deprecations+Removals.swift */; };
 		9ABCB1861D2A5B5A00BCA243 /* Deprecations+Removals.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9ABCB1841D2A5B5A00BCA243 /* Deprecations+Removals.swift */; };
 		9ABCB1871D2A5B5A00BCA243 /* Deprecations+Removals.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9ABCB1841D2A5B5A00BCA243 /* Deprecations+Removals.swift */; };
@@ -923,6 +927,7 @@
 		7A7065831A3F8967001E8354 /* RACKVOProxySpec.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = RACKVOProxySpec.m; sourceTree = "<group>"; };
 		7DFBED031CDB8C9500EE435B /* ReactiveCocoaTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = ReactiveCocoaTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 		9A1E72B91D4DE96500CC20C3 /* KeyValueObservingSpec.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = KeyValueObservingSpec.swift; sourceTree = "<group>"; };
+		9A694EF21D5CE02E009B05BD /* UnidirectionalBinding.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UnidirectionalBinding.swift; sourceTree = "<group>"; };
 		9ABCB1841D2A5B5A00BCA243 /* Deprecations+Removals.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "Deprecations+Removals.swift"; sourceTree = "<group>"; };
 		9AD0F0691D48BA4800ADFAB7 /* NSObject+KeyValueObserving.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "NSObject+KeyValueObserving.swift"; sourceTree = "<group>"; };
 		A97451331B3A935E00F48E55 /* watchOS-Application.xcconfig */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.xcconfig; path = "watchOS-Application.xcconfig"; sourceTree = "<group>"; };
@@ -1622,6 +1627,7 @@
 				D08C54B01A69A2AC00AD8286 /* Property.swift */,
 				D08C54B11A69A2AC00AD8286 /* Signal.swift */,
 				D08C54B21A69A2AC00AD8286 /* SignalProducer.swift */,
+				9A694EF21D5CE02E009B05BD /* UnidirectionalBinding.swift */,
 			);
 			name = Signals;
 			sourceTree = "<group>";
@@ -2427,6 +2433,7 @@
 				57A4D1F81BA13D7A00F7D4B1 /* RACSignalSequence.m in Sources */,
 				57A4D1F91BA13D7A00F7D4B1 /* RACStream.m in Sources */,
 				57A4D1FA1BA13D7A00F7D4B1 /* RACStringSequence.m in Sources */,
+				9A694EF61D5CE02E009B05BD /* UnidirectionalBinding.swift in Sources */,
 				CD0C45E11CC9A288009F5BF0 /* DynamicProperty.swift in Sources */,
 				57A4D1FB1BA13D7A00F7D4B1 /* RACSubject.m in Sources */,
 				57A4D1FC1BA13D7A00F7D4B1 /* RACSubscriber.m in Sources */,
@@ -2578,6 +2585,7 @@
 				A9B3158D1B3940750001CB9C /* RACKVOTrampoline.m in Sources */,
 				A9B3158E1B3940750001CB9C /* RACMulticastConnection.m in Sources */,
 				C7142DBE1CDEA194009F402D /* CocoaAction.swift in Sources */,
+				9A694EF51D5CE02E009B05BD /* UnidirectionalBinding.swift in Sources */,
 				A9B315901B3940750001CB9C /* RACPassthroughSubscriber.m in Sources */,
 				A9B315911B3940750001CB9C /* RACQueueScheduler.m in Sources */,
 				A9B315921B3940750001CB9C /* RACReplaySubject.m in Sources */,
@@ -2623,6 +2631,7 @@
 				D03765D819EDA41200A782A9 /* RACSignal+Operations.m in Sources */,
 				D871D69F1B3B29A40070F16C /* Optional.swift in Sources */,
 				D08C54B61A69A3DB00AD8286 /* Event.swift in Sources */,
+				9A694EF31D5CE02E009B05BD /* UnidirectionalBinding.swift in Sources */,
 				D03764F219EDA41200A782A9 /* NSControl+RACTextSignalSupport.m in Sources */,
 				D037650219EDA41200A782A9 /* NSFileHandle+RACSupport.m in Sources */,
 				D03765E219EDA41200A782A9 /* RACStream.m in Sources */,
@@ -2874,6 +2883,7 @@
 				D037662319EDA41200A782A9 /* UIBarButtonItem+RACCommandSupport.m in Sources */,
 				D03765A119EDA41200A782A9 /* RACKVOTrampoline.m in Sources */,
 				D037665B19EDA41200A782A9 /* UITableViewHeaderFooterView+RACSignalSupport.m in Sources */,
+				9A694EF41D5CE02E009B05BD /* UnidirectionalBinding.swift in Sources */,
 				D0C312D019EF2A5800984962 /* Bag.swift in Sources */,
 				D0D11ABA1A6AE87700C1F8B1 /* Action.swift in Sources */,
 				D037650B19EDA41200A782A9 /* NSInvocation+RACTypeParsing.m in Sources */,

ReactiveCocoa/Swift/DynamicProperty.swift

@@ -36,6 +36,11 @@ public final class DynamicProperty<Value>: MutablePropertyProtocol {
 		}
 	}
 
+	/// The lifetime of the property.
+	public var lifetime: Lifetime {
+		return object?.rac_lifetime ?? .empty
+	}
+
 	/// A producer that will create a Key-Value Observer for the given object,
 	/// send its initial value then all changes over time, and then complete
 	/// when the observed object has deallocated.

ReactiveCocoa/Swift/Lifetime.swift

@@ -4,9 +4,28 @@ import enum Result.NoError
 /// Represents the lifetime of an object, and provides a hook to observe when
 /// the object deinitializes.
 public final class Lifetime {
-	/// A signal that sends a Completed event when the lifetime ends.
+	/// MARK: Type properties and methods
+
+	/// A `Lifetime` that has already ended.
+	public static var empty: Lifetime {
+		return Lifetime(ended: .empty)
+	}
+
+	/// MARK: Instance properties
+
+	/// A signal that sends a `completed` event when the lifetime ends.
 	public let ended: Signal<(), NoError>
 
+	/// MARK: Initializers
+
+	/// Initialize a `Lifetime` object with the supplied ended signal.
+	///
+	/// - parameters:
+	///   - signal: The ended signal.
+	private init(ended signal: Signal<(), NoError>) {
+		ended = signal
+	}
+
 	/// Initialize a `Lifetime` from a lifetime token, which is expected to be
 	/// associated with an object.
 	///
@@ -16,8 +35,8 @@ public final class Lifetime {
 	/// - parameters:
 	///   - token: A lifetime token for detecting the deinitialization of the
 	///            associated object.
-	public init(_ token: Token) {
-		ended = token.ended
+	public convenience init(_ token: Token) {
+		self.init(ended: token.ended)
 	}
 
 	/// A token object which completes its signal when it deinitializes.