swift 错误处理do catch try try!使用详解

//
//  AboutError.swift
//  learn_swiftUi
//
//  Created by liuan on 2020/9/4.
//  Copyright © 2020 liuan. All rights reserved.
//

import Foundation
enum VendingMachingError:Error{
    case invalideSelection
    case insufficientFunds(coinsNeeded:Int)
    case outOfStock
}

func canThrowErrors() throws -> String

//
//  AboutError.swift
//  learn_swiftUi
//
//  Created by liuan on 2020/9/4.
//  Copyright © 2020 liuan. All rights reserved.
//

import Foundation
enum VendingMachingError:Error{
    case invalideSelection
    case insufficientFunds(coinsNeeded:Int)
    case outOfStock
}
struct Item {
    var price: Int
    var count: Int
}

class VendingMathine{
    var inventory=[
        "Candy bar":Item(price: 12, count: 7),
        "Chips":Item(price: 10, count: 4),
        "Pretzels":Item(price: 7, count: 11),
    ]
    
    var coinsDeposited = 0
    func vend(itemNaamed name:String) throws{
        guard let item = inventory[name] else{
            throw VendingMachingError.invalideSelection
        }
        
        guard item.count > 0 else{
            throw VendingMachingError.outOfStock
        }
        guard item.price <= coinsDeposited else{
            throw VendingMachingError.insufficientFunds(coinsNeeded: item.price - coinsDeposited)
             }
        
        coinsDeposited -= item.price
        var newItem = item
        newItem.count -= 1
        inventory[name]=newItem
        print("Dispensing \(name)")
        
    }
}


let vm=VendingMathine()

vm.coinsDeposited=2
try vm.vend(itemNaamed: "Pretzels")

Playground execution terminated: An error was thrown and was not caught:
▿ VendingMachingError
  ▿ insufficientFunds : 1 element
    - coinsNeeded : 5

//
//  AboutError.swift
//  learn_swiftUi
//
//  Created by liuan on 2020/9/4.
//  Copyright © 2020 liuan. All rights reserved.
//

import Foundation
let photo = try! 5/0

warning: BlackMyPlayground.playground:10:19: warning: no calls to throwing functions occur within 'try' expression
let photo = try! 5/0
                  ^

warning: BlackMyPlayground.playground:10:19: warning: no calls to throwing functions occur within 'try' expression
let photo = try! 5/0
                  ^

error: BlackMyPlayground.playground:10:19: error: division by zero
let photo = try! 5/0
                  ^

//
//  File.swift
//  learn_swiftUi
//
//  Created by liuan on 2020/9/4.
//  Copyright © 2020 liuan. All rights reserved.
//

import Foundation

func processFile(fileName: String)throws{
    defer{
        print("JIESHU")
    }
   print("KAISHI ")
 
}