Adds race task

[flovilmart]

Adds a race task, been using that code in a category in production apps for a while.
Heavily inspired by the taskForCompletionOfAll:

[nlutsenko]

Wonderful! Yes, this is helpful for everyone, and is surfaced on Android as whenAny.
Meaning that here it would be taskForCompletionOfAnyTask: 😁

Will review code in detail in a little bit, but the first thing - can we rename it to taskForCompletionOfAnyTask:.
Slightly a longer name, I know, but overall - it describes intention better.

[flovilmart]

taskForCompletionOfAnyTask: suggest that it requires completion involved. race: implies that the faster to return would be the one... I dunno, I like the conciseness of race (and I have it implemented in about 10 projects)

[flovilmart]

@nlutsenko adding more tests, support for nullable array and rename the method

[nlutsenko]

Going to nitpick on stuff here, but will try my best to review the entire thing right now.

[nlutsenko]

Nit: Space before else.

[nlutsenko]

Tried my best to review everything. There are few important pieces (usage of dispatch once predicate and constants instead of magic strings), but overall - it looks complete and nice.

Discussion piece:
Do you think it would be beneficial to have a taskForCompletionOfAnyTask:cancellationToken: in addition to this one? Most of our methods do have it, but I actually don't think it's that much helpful, plus it changes the semantics of how we treat cancellation, as we probably should cancel the whole task altogether if the token is cancelled.
Just throwing this here for discussion and curious to know your opinion on this.

[flovilmart]

for the cancellation token, I believe that can be problematic. It's heavily inspired by + (instancetype)taskForCompletionOfAllTasks:(nullable NSArray<BFTask *> *)tasks; that don't have cancellation tokens, and I believe for the same reason. If tasks need a cancellation token, they should be cancellable by themselves don't you think?

[nlutsenko]

Cancellable by themselves - maybe, though I sort of can see a situation where you would want to have an ability to cancel the entire chain that ends with AnyTask if say a person quite from the view, but still send the updates to the server. Up to you if you want to build another method for it here (we probably would want 2 methods one with token one without to match other APIs).

[nlutsenko]

I feel like you can unify this as else statement on the above condition. Also, there is no way this task is not going to be completed here, since continueWithBlock: is called only after it's completed.

[nlutsenko]

Nit: Remove space before task.

[nlutsenko]

Almost there. Few nits here and there and almost ready to go.
Also, you might want to use generics for those NSMutableArrays on the stack, since it will enforce that you can only add NSError/NSException to them.

[facebook-github-bot]

@flovilmart updated the pull request.