Swift Error Handling

viewController.swift

//
//  ViewController.swift
//  ErrorTest
//
//  Created by ZhuJiang on 2017/8/15.
//  Copyright © 2017年 Charles. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        do {
            try errorTest(num: -10.0)
        } catch let error {
            print("\(error)")
        }
        
        let x = try? errorTest(num: -10.0)
        print(type(of: x))
        
        let y = try? errorTest(num: 10.0)
        print(type(of: y))
        
        let z = try! errorTest(num: 10.0) //crash if it is -10.0
        print(type(of: z))
    }


    enum ZZNumberError : Error { case negativeError }
    
    private func errorTest(num: Double) throws -> Double {
        if num < 0 {
            throw ZZNumberError.negativeError
        }
        return num
    }
    

    
    
    
}