Several types of variables in Swift

Several types of variables in Swift

The variables in swift are divided into optional,non-optional and implicitly unwrapped optional these types

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

Among them,optional (such as anyobject? ) values can contain nil values, and ( anyobject! ) is not a nil value, it will crash when forced to expand without a value; Anyobject) must be assigned in advance to be able to use it, and no value will crash after forced expansion

The following are the correspondence between several variables and OC variables

Attached source

 
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)
    }
}

Several types of variables in Swift