Add map(to:) operator

CHANGELOG.md

@@ -1,6 +1,8 @@
 # master
 *Please add new entries at the top.*
 
+1. New operator `map(value:)` (#601, kudos to @ra1028)
+
 # 3.1.0
 1. Fixed `schedule(after:interval:leeway:)` being cancelled when the returned `Disposable` is not retained. (#584, kudos to @jjoelson)
 

Sources/Property.swift

@@ -101,6 +101,16 @@ extension PropertyProtocol {
 	public func map<U>(_ transform: @escaping (Value) -> U) -> Property<U> {
 		return lift { $0.map(transform) }
 	}
+
+	/// Map the current value and all susequent values to a new constant property.
+	///
+	/// - parameters:
+	///   - value: A new value.
+	///
+	/// - returns: A property that holds a mapped value from `self`.
+	public func map<U>(value: U) -> Property<U> {
+		return lift { $0.map(value: value) }
+	}
 
 	/// Maps the current value and all subsequent values to a new property
 	/// by applying a key path.

Sources/Signal.swift

@@ -557,6 +557,16 @@ extension Signal {
 	public func map<U>(_ transform: @escaping (Value) -> U) -> Signal<U, Error> {
 		return flatMapEvent(Signal.Event.map(transform))
 	}
+
+	/// Map each value in the signal to a new constant value.
+	///
+	/// - parameters:
+	///   - value: A new value.
+	///
+	/// - returns: A signal that will send new values.
+	public func map<U>(value: U) -> Signal<U, Error> {
+		return map { _ in value }
+	}
 
 	/// Map each value in the signal to a new value by applying a key path.
 	///

Sources/SignalProducer.swift

@@ -857,6 +857,17 @@ extension SignalProducer {
 	public func map<U>(_ transform: @escaping (Value) -> U) -> SignalProducer<U, Error> {
 		return core.flatMapEvent(Signal.Event.map(transform))
 	}
+
+	/// Map each value in the producer to a new constant value.
+	///
+	/// - parameters:
+	///   - value: A new value.
+	///
+	/// - returns: A signal producer that, when started, will send a mapped
+	///            value of `self`.
+	public func map<U>(value: U) -> SignalProducer<U, Error> {
+		return lift { $0.map(value: value) }
+	}
 
 	/// Map each value in the producer to a new value by applying a key path.
 	///

Tests/ReactiveSwiftTests/PropertySpec.swift

@@ -732,13 +732,21 @@ class PropertySpec: QuickSpec {
 			describe("map") {
 				it("should transform the current value and all subsequent values") {
 					let property = MutableProperty(1)
-					let mappedProperty = property
-						.map { $0 + 1 }
+					let mappedProperty = property.map { $0 + 1 }
 					expect(mappedProperty.value) == 2
 
 					property.value = 2
 					expect(mappedProperty.value) == 3
 				}
+
+				it("should transform the current value and all subsequent values to a constant value") {
+					let property = MutableProperty("foo")
+					let mappedProperty = property.map(value: 1)
+					expect(mappedProperty.value) == 1
+
+					property.value = "foobar"
+					expect(mappedProperty.value) == 1
+				}
 
 				it("should work with key paths") {
 					let property = MutableProperty("foo")

Tests/ReactiveSwiftTests/SignalProducerLiftingSpec.swift

@@ -36,6 +36,25 @@ class SignalProducerLiftingSpec: QuickSpec {
 				observer.send(value: 1)
 				expect(lastValue) == "2"
 			}
+
+			it("should raplace the values of the signal to constant new value") {
+				let (producer, observer) = SignalProducer<String, NoError>.pipe()
+				let mappedProducer = producer.map(value: 1)
+
+				var lastValue: Int?
+
+				mappedProducer.startWithValues {
+					lastValue = $0
+				}
+
+				expect(lastValue).to(beNil())
+
+				observer.send(value: "foo")
+				expect(lastValue) == 1
+
+				observer.send(value: "foobar")
+				expect(lastValue) == 1
+			}
 		}
 
 		describe("mapError") {

Tests/ReactiveSwiftTests/SignalSpec.swift

@@ -506,9 +506,9 @@ class SignalSpec: QuickSpec {
 				expect(lastValue) == "2"
 			}
 
-			it("should support key paths") {
+			it("should replace the values of the signal to constant new value") {
 				let (signal, observer) = Signal<String, NoError>.pipe()
-				let mappedSignal = signal.map(\String.count)
+				let mappedSignal = signal.map(value: 1)
 
 				var lastValue: Int?
 				mappedSignal.observeValues {
@@ -518,8 +518,26 @@ class SignalSpec: QuickSpec {
 				expect(lastValue).to(beNil())
 
 				observer.send(value: "foo")
-				expect(lastValue) == 3
+				expect(lastValue) == 1
 
+				observer.send(value: "foobar")
+				expect(lastValue) == 1
+			}
+
+			it("should support key paths") {
+				let (signal, observer) = Signal<String, NoError>.pipe()
+				let mappedSignal = signal.map(\String.count)
+
+				var lastValue: Int?
+				mappedSignal.observeValues {
+					lastValue = $0
+				}
+
+				expect(lastValue).to(beNil())
+
+				observer.send(value: "foo")
+				expect(lastValue) == 3
+
 				observer.send(value: "foobar")
 				expect(lastValue) == 6
 			}