// Spring animation
view.yaal.center.animateTo(CGPoint(x:50, y:100))
view.yaal.alpha.animateTo(0.5, stiffness: 300, damping: 20)

// Curve(Basic) animation
view.yaal.frame.animateTo(CGRect(x:0, y:0, width:50, height:50), duration:0.5, curve: .linear)

// Decay Animation
view.yaal.center.decay(initialVelocity:CGPoint(x:100, y:0))

// observe value changes
view.yaal.center.value.changes.addListener { oldVelocity, newVelocity in
  print(oldVelocity, newVelocity)
}
// observe velocity changes
view.yaal.center.velocity.changes.addListener { oldVelocity, newVelocity in
  print(oldVelocity, newVelocity)
}

// when scale changes, also change its alpha
// for example if view's scale animates from 1 to 0.5. its alpha will animate to 0.5 as well
view.yaal.scale.value => view.yaal.alpha
// equvalent to the following
// view.yaal.scale.value.changes.addListener { _, newScale in
//   view.yaal.alpha.animateTo(newScale)
// }

// optionally you can provide a mapping function in between.
// For example, the following code makes the view more transparent the faster it is moving
view.yaal.center.velocity => { 1 - $0.magnitude / 1000 } => view.yaal.alpha
// equvalent to the following
// view.yaal.center.velocity.changes.addListener { _, newVelocity in
//   view.yaal.alpha.animateTo(1 - newVelocity.magnitude / 1000)
// }

// this sets the value directly (not animate to). Change listeners are called.
// Velocity listeners will receive a series of smoothed velocity values.
view.yaal.center.setTo(gestureRecognizer.location(in:nil))

   override func viewDidLoad() {
     // ...
     view.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(tap(gr:))))
     squareView.yaal.center.velocity => { $0.x / 1000 } => squareView.yaal.rotation
   }
   func tap(gr: UITapGestureRecognizer) {
       squareView.yaal.center.animateTo(gr.location(in: view))
   }

override func viewDidLoad() {
    // ...
    squareView.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(pan(gr:))))
    squareView.yaal.perspective.setTo(-1.0 / 500.0)
    squareView.yaal.center.velocity => { $0.x / 1000 } => squareView.yaal.rotationY
    squareView.yaal.center.velocity => { -$0.y / 1000 } => squareView.yaal.rotationX
}

func pan(gr: UIPanGestureRecognizer) {
    squareView.yaal.center.setTo(gr.location(in: view))
}

class Foo {
    var volumn: Float = 0.0
    lazy var volumnAnimation: SpringAnimation<Float>
        = SpringAnimation(getter: { [weak self] in self?.volumn },
                          setter: { [weak self] in self?.volumn = $0 })
}

volumnAnimation.animateTo(0.5)

extension Foo {
    public var volumnAnimation: MixAnimation<CGRect> {
        return yaal.animationFor(key: "volumn",
                                 getter: { [weak self] in self?.volumn },
                                 setter: { [weak self] in self?.volumn = $0 })
    }
}

// or register ahead of time
yaal.register(key: "volumn", 
              getter: { [weak self] in self?.volumn },
              setter: { [weak self] in self?.volumn = $0 })

// and retrieve the animation object through the same key.
yaal.animationFor(key: "volumn")!.animateTo(0.5)

// NOTE: that this method have limited type safety. You can basically pass any animatable type into `animateTo()`
// There is nothing to stop you from doing the following. but they will crash at run time
yaal.animationFor(key: "volumn")!.animateTo(CGSize.zero)
yaal.animationFor(key: "volumn")!.animateTo(CGRect.zero)

// the following makes IndexPath animatable
extension IndexPath: VectorConvertible {
    public typealias Vector = Vector2
    public init(vector: Vector) {
        self.init(item: Int(vector.x), section: Int(vector.y))
    }
    public var vector: Vector {
        return [Double(item), Double(section)]
    }
}
// Can now be used like this
let indexAnimation = SpringAnimation(getter: { self.indexPath },
                                     setter: { self.indexPath = $0 })
indexAnimation.animateTo(IndexPath(item:0, section:0))

// Note that everything is type safe. incorrect type won't be allowed to compile