Animator

Manages the application of animations to a value.

let view = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))

let sizeAnimator = Animator(initialValue: view.bounds.size)
sizeAnimator.onChange = { view.bounds.size = $0 }

/// Spring physics will move the view's size to the new value.
sizeAnimator.spring(to: CGSize(width: 300, height: 300))

/// Some time in the future...

/// The value will keep the same velocity that it had from the preceeding
/// animation, and a decay function will slowly bring movement to a stop.
sizeAnimator.decay(drag: 2.0)

Timing functions are used to convert linear input time (0.0 -> 1.0) to transformed output time (also 0.0 -> 1.0).

A bezier curve, often used to calculate timing functions.