Observable is the easiest way to observe values in Swift.

var position = Observable(CGPoint.zero)

var position = Observable(CGPoint.zero)
var immutablePosition: ImmutableObservable<CGPoint> = position 
// With an ImmutableObservable the value can't be changed, only read or observe it's value changes

position.observe { p in
    // handle new position
}

position.observe(DispatchQueue.main) { p in
// handle new position
}

position.value = p

For a single observer you can store the returned Disposable to a variable

disposable = position.observe { p in

For multiple observers you can add the disposable to a Disposal variable

position.observe { }.add(to: &disposal)

And always weakify self when referencing self inside your observer

position.observe { [weak self] position in

Observable is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'Observable'

Observable is available through Carthage. To install it, simply add the following line to your Cartfile:

github "roberthein/Observable" "master"

Feel free to create a pull request, open an issue or find me on Twitter.