Implementing tasks that can be canceled in Bolts Framework (BFTask)

BFTask has been good to me but I have one complaint: I've yet to see a working example of how you ought to cancel a task. The entirety of the documentation on the subject is found on their GitHub page with a single lowly section that includes everything but the part I care about: how to cancel the task.

// Somewhere else.
MYCancellationToken *cancellationToken = [[MYCancellationToken alloc] init];
[obj doSomethingComplicatedAsync:cancellationToken];

// When you get bored...
[cancellationToken cancel];

Their code snippet is followed by:

Note: The cancellation token implementation should be thread-safe.

I am wondering the following:

1. Is there a good reason that they may not have provided the cancel method on the BFTask interface itself? They have a property representing whether the task was canceled but no means to cancel it.
2. Is there a good reason that they would not include a cancellationToken(s) property on the BFTask itself?
3. Is the implementation of cancel strongly coupled to the task itself? Or is a general implementation possible as in the case of cancelAllOperations of an NSOperationQueue?

1. As you might know, BFTask is an implementation of the Future and Promises construct:
   "a future is a read-only placeholder view of a variable, while a promise is a writable, single assignment container which sets the value of the future".
   Basically, a BFTask is a Future: it is a read-only placeholder view of a variable.
   A BFTaskCompletionSource is a promise: it is a writable, single assignment container which sets the value of the future. (or an error - or cancels the task)
   The BFTask public interface remains read-only , hence it does not allow you to cancel it directly.
2. This has the same answer as the previous question: BFTask is read-only and represents a read-only value. Exposing cancellation tokens would allow you to manipulate the task, which is contradictory to its nature.
3. Let's take a look at it: https://github.com/BoltsFramework/Bolts-iOS/blob/master/Bolts/Common/BFCancellationToken.m The BFCancellationToken token just stores a state, which the BFTask can check. Your async task code can basically regularly check cancellationRequested is set to true, which allows you to manually cancel your task.
   
   Note: The Bolts Framework iOS docs say: "A task is kind of like a JavaScript Promise" which can be confusing, because it really is a Future. I think it was just named wrong in its Javascript origins.