Closure based CATransaction API

CATransaction+Closure.swift

import UIKit

// I'm not sure how useful this is, but swift allows for a somewhat elegant closure base API for CATransation.
// Each argument if optional, so it can be omitted unless necessary. It's a little weird having the completion
// block come before the actions block, but this way the actions block can make sure of trailing closure syntax.
extension CATransaction {
    static func transaction(duration: CFTimeInterval? = nil,
                            timingFunction: CAMediaTimingFunction? = nil,
                            disableActions: Bool? = nil,
                            completion: (() -> Void)? = nil,
                            actions: () -> Void) {
        begin()
        duration.flatMap { setAnimationDuration($0) }
        timingFunction.flatMap { setAnimationTimingFunction($0) }
        disableActions.flatMap { setDisableActions($0) }
        completion.flatMap { setCompletionBlock($0) }
        actions()
        commit()
    }
}

// sample usage
let layer = CALayer()
CATransaction.transaction {
    layer.backgroundColor = UIColor.red.cgColor
}
CATransaction.transaction(disableActions: true) {
    layer.backgroundColor = UIColor.blue.cgColor
}
CATransaction.transaction(duration: 3) {
    layer.backgroundColor = UIColor.green.cgColor
}
CATransaction.transaction(duration: 3, timingFunction: CAMediaTimingFunction(name: .easeInEaseOut)) {
    layer.backgroundColor = UIColor.yellow.cgColor
}
CATransaction.transaction(completion: {
    print("completed")
}) {
    layer.backgroundColor = UIColor.cyan.cgColor
}