Fix for await function

[ignazioc]

I'm trying to use await using the syntax from the readme.

let city = try await(getCityPromise())

The getCityPromise function is declared like this:

func getCityPromise() -> Promise<String> { ... } 

But the compiler raises an error

cannot invoke 'await' with an argument list of type '(Promise<String>)'

Then I looked at the unit tests, and I saw that a special operator .. is used instead of calling the await function.

Using that operator my code doesn't raise any error anymore. Should the documentation be fixed or I'm missing something?

[malcommac]

It's a mistake with non labeled parameters 👎
I've solved it in b2323a9 and it will be released with 0.9.2.

Due to the fact we can't provide a behaviour like in C#, in order to avoid block of the current thread (ie. the main thread) I suggest you to do await operations in another queue by adding it inside an async closure.
That's the example fixed inside the README:

// With `async` we have just defined a Promise which will be executed in a given
// context (if omitted `background` thread is used) and return an Int value.
let asyncFunc = async({ _ -> Int // you must specify the return of the Promise, here an Int
    // With `await` the async code is resolved in a sync manner
    let loggedUser = try await(loginUser(username,pass))
    // one promise...
    let followersList = try await(getFollowers(loggedUser))
    // after another...
    let countUnfollowed = try await(unfollow(followersList))
    // ... linearly
    // Then our async promise will be resolved with the end value
    return countUnfollowed
}).then({ value in // ... and, like a promise, the value is returned
    print("Unfollowed \(value) users")
})

[malcommac]

This is how the operator are defined:

With .. the call is allowed to throws in case of Promise's failure.

/// This define a `..` operator you can use instead of calling `await` func.
/// If you use this operator you need to also use `do/catch` in order to catch exception for rejected promises.
prefix operator ..
public prefix func ..<T> (_ promise: Promise<T>) throws -> T {
	return try awaitContext.await(promise)
}

While using ..! if it fails it will return nil.

// This define a `..!` operator you can use instead of calling `await`.
// Using this operator if promise is rejected for any reason the result is `nil` and no throws is called.
prefix operator ..!
public prefix func ..!<T> (_ promise: Promise<T>) -> T? {
	do {
		return try awaitContext.await(promise)
	} catch {
		return nil
	}
}