swift中变量的几种类型

        var nullableProperty    : AnyObject? // optional
        var nonNullProperty     : AnyObject  // non-optional
        var unannotatedProperty : AnyObject! // implicitly unwrapped optional

import UIKit

class ViewController: UIViewController {
    
    override func viewDidLoad() {
        
        super.viewDidLoad()
        
        var nullableProperty    : AnyObject? // optional
        var nonNullProperty     : AnyObject  // non-optional
        var unannotatedProperty : AnyObject! // implicitly unwrapped optional
        
        nullableProperty    = UIColor.redColor()
        nonNullProperty     = UIColor.redColor()
        unannotatedProperty = UIColor.redColor()
        
        print(nullableProperty)
        print(nonNullProperty)
        print(unannotatedProperty)
    }
}