UIView, UIButton subclass with custom drawing method set on init

DrawingView.swift

//  DrawingView by Clément Cyril - @clmntcrl - http://clmntcrl.io/
//  Copyright 2015 Clément Cyril.

import UIKit

class DrawingView: UIView {

    var draw: CGRect -> Void = { _ in } {
        didSet { setNeedsDisplay() }
    }

    convenience init(frame: CGRect, draw drawingClosure: CGRect -> Void) {
        self.init(frame: frame)
        draw = drawingClosure
    }

    override func drawRect(rect: CGRect) {
        draw(rect)
    }
}

class DrawingButton: UIButton {

    var draw: CGRect -> Void = { _ in } {
        didSet { setNeedsDisplay() }
    }

    convenience init(frame: CGRect, draw drawingClosure: CGRect -> Void) {
        self.init(frame: frame)
        draw = drawingClosure
    }

    override func drawRect(rect: CGRect) {
        draw(rect)
    }
}