'Cancel' for PromiseKit --

* Eliminate duplicate code in the cancellable extensions
* When using the 'cancellable' function with the extensions, ensure that the underlying task (if any) is always cancelled
* When using the 'cancellable' function, call 'reject' on the underlying promise (wherever possible) if 'cancel' is invoked
* Create cancellable wrappers for the extensions only for the cases where there is an underlying task that supports cancellation

Author: dougzilla32

Sources/MKDirections+Promise.swift

@@ -16,18 +16,16 @@ import PromiseKit
 extension MKDirections {
     /// Begins calculating the requested route information asynchronously.
     public func calculate() -> Promise<MKDirectionsResponse> {
-        return Promise { calculate(completionHandler: $0.resolve) }
+        return Promise(cancellableTask: MKDirectionsTask(self)) { calculate(completionHandler: $0.resolve) }
     }
 
     /// Begins calculating the requested travel-time information asynchronously.
     public func calculateETA() -> Promise<MKETAResponse> {
-        return Promise { calculateETA(completionHandler: $0.resolve) }
+        return Promise(cancellableTask: MKDirectionsTask(self)) { calculateETA(completionHandler: $0.resolve) }
     }
 }
 
-//////////////////////////////////////////////////////////// Cancellation
-
-fileprivate class MKDirectionsTask: CancellableTask {
+private class MKDirectionsTask: CancellableTask {
     let directions: MKDirections
     var cancelAttempted = false
 
@@ -45,14 +43,16 @@ fileprivate class MKDirectionsTask: CancellableTask {
     }
 }
 
+//////////////////////////////////////////////////////////// Cancellable wrappers
+
 extension MKDirections {
     /// Begins calculating the requested route information asynchronously.
     public func cancellableCalculate() -> CancellablePromise<MKDirectionsResponse> {
-        return CancellablePromise(task: MKDirectionsTask(self)) { calculate(completionHandler: $0.resolve) }
+        return cancellable(calculate())
     }
 
     /// Begins calculating the requested travel-time information asynchronously.
     public func cancellableCalculateETA() -> CancellablePromise<MKETAResponse> {
-        return CancellablePromise(task: MKDirectionsTask(self)) { calculateETA(completionHandler: $0.resolve) }
+        return cancellable(calculateETA())
     }
 }

Sources/MKMapSnapshotter+Promise.swift

@@ -16,13 +16,11 @@ import PromiseKit
 extension MKMapSnapshotter {
     /// Starts generating the snapshot using the options set in this object.
     public func start() -> Promise<MKMapSnapshot> {
-        return Promise { start(completionHandler: $0.resolve) }
+        return Promise(cancellableTask: MKMapSnapshotterTask(self)) { start(completionHandler: $0.resolve) }
     }
 }
 
-//////////////////////////////////////////////////////////// Cancellation
-
-fileprivate class MKMapSnapshotterTask: CancellableTask {
+private class MKMapSnapshotterTask: CancellableTask {
     let snapshotter: MKMapSnapshotter
     var cancelAttempted = false
 
@@ -40,9 +38,11 @@ fileprivate class MKMapSnapshotterTask: CancellableTask {
     }
 }
 
+//////////////////////////////////////////////////////////// Cancellable wrapper
+
 extension MKMapSnapshotter {
     /// Starts generating the snapshot using the options set in this object.
     public func cancellableStart() -> CancellablePromise<MKMapSnapshot> {
-        return CancellablePromise(task: MKMapSnapshotterTask(self)) { start(completionHandler: $0.resolve) }
+        return cancellable(start())
     }
 }