Add ifEmpty operators on Maybe

RxSwift/Traits/Maybe.swift

@@ -241,4 +241,40 @@ public extension PrimitiveSequenceType where TraitType == MaybeTrait {
         -> Maybe<R> {
             return Maybe<R>(raw: primitiveSequence.source.flatMap(selector))
     }
+
+    /**
+     Emits elements from the source observable sequence, or a default element if the source observable sequence is empty.
+
+     - seealso: [DefaultIfEmpty operator on reactivex.io](http://reactivex.io/documentation/operators/defaultifempty.html)
+
+     - parameter default: Default element to be sent if the source does not emit any elements
+     - returns: An observable sequence which emits default element end completes in case the original sequence is empty
+     */
+    public func ifEmpty(default: ElementType) -> Maybe<ElementType> {
+        return Maybe(raw: primitiveSequence.source.ifEmpty(default: `default`))
+    }
+
+    /**
+     Returns the elements of the specified sequence or `switchTo` sequence if the sequence is empty.
+
+     - seealso: [DefaultIfEmpty operator on reactivex.io](http://reactivex.io/documentation/operators/defaultifempty.html)
+
+     - parameter switchTo: Observable sequence being returned when source sequence is empty.
+     - returns: Observable sequence that contains elements from switchTo sequence if source is empty, otherwise returns source sequence elements.
+     */
+    public func ifEmpty(switchTo other: Maybe<ElementType>) -> Maybe<ElementType> {
+        return Maybe(raw: primitiveSequence.source.ifEmpty(switchTo: other.primitiveSequence.source))
+    }
+
+    /**
+     Returns the elements of the specified sequence or `switchTo` sequence if the sequence is empty.
+
+     - seealso: [DefaultIfEmpty operator on reactivex.io](http://reactivex.io/documentation/operators/defaultifempty.html)
+
+     - parameter switchTo: Observable sequence being returned when source sequence is empty.
+     - returns: Observable sequence that contains elements from switchTo sequence if source is empty, otherwise returns source sequence elements.
+     */
+    public func ifEmpty(switchTo other: Single<ElementType>) -> Single<ElementType> {
+        return Single(raw: primitiveSequence.source.ifEmpty(switchTo: other.primitiveSequence.source))
+    }
 }

Tests/RxSwiftTests/MaybeTest.swift

@@ -585,6 +585,49 @@ extension MaybeTest {
             .completed(200)
             ])
     }
+
+    func test_ifEmptyDefault() {
+        let scheduler = TestScheduler(initialClock: 0)
+
+        let res = scheduler.start {
+            (Maybe<Int>.empty().ifEmpty(default: 5).asObservable())
+        }
+
+        XCTAssertEqual(res.events, [
+            next(200, 5),
+            completed(200)
+            ])
+    }
+
+    func test_ifEmptySwitchToMaybe() {
+        let scheduler = TestScheduler(initialClock: 0)
+        let source = Maybe<Int>.empty()
+        let switchSource = Maybe.just(10)
+
+        let res = scheduler.start {
+            (source.ifEmpty(switchTo: switchSource).asObservable())
+        }
+
+        XCTAssertEqual(res.events, [
+            next(200, 10),
+            completed(200)
+            ])
+    }
+
+    func test_ifEmptySwitchToSingle() {
+        let scheduler = TestScheduler(initialClock: 0)
+        let source = Maybe<Int>.empty()
+        let switchSource = Single.just(10)
+
+        let res = scheduler.start {
+            (source.ifEmpty(switchTo: switchSource).asObservable())
+        }
+
+        XCTAssertEqual(res.events, [
+            next(200, 10),
+            completed(200)
+            ])
+    }
 }
 
 extension MaybeTest {