Simple, straightforward, promise library written in Swift.
A promise represents the eventual value or error that is provided by an asynchronous function.
To interact with a promise's eventual value or error, we give the promise a new callback by calling then with a fulfilled block and a rejected block.
In this example, assume fetchName is some function that returns a promise. The promise will be either fulfilled with a name (String) if the async operation completes, or rejected with an error (NSError) if async operation fails.
fetchName.then({ (name: String) in
// fetched name successfully
println("Hello, \(name)!")
}, { (error: NSError) in
// failed to fetch name
println(error)
})