UIImage extension

emptyImage.swift

// https://twitter.com/dwineman/status/601853359839006721
// Default arguments are expressions, not constants, evaluated only when necessary. 

extension UIImage {
    static func emptyImage(size: CGSize, scale: CGFloat = UIScreen.mainScreen().scale) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
}