Swift中optionals使用总结

Github链接：https://github.com/andyRon/LearnSwift/blob/master/Tips/Swift中optionals使用总结.md

1. 变量声明

let optional: String? = "unicorn"
var optional2: Int?
let optionals: [String?] = ["unicorn", nil, "dragon"]
var optionals2: [Int]?

2. if let

if let value = optional {

// 多变量
if let value = optional, let value2 = optional2 {

// 布尔值判断从句（boolean clause）
if let value = optional, value.hasSuffix("saurus") {

3. guard

guard let value = optional else { 
  return
}

4. while

while let value = optional {

5. 空合运算（(Nil Coalescing）

let value = optional ?? "nil"

6. 强制解析

let value = optional!

7. switch

switch optional {
case .some(let value):
  print(value)
case .none:
  print("nil")
}

8. map()

let value = optional.map(String.init(describing:))

9. flatMap()

let value = optional.flatMap(URL.init(string:))

10. compactMap()

let values = optionals.compactMap { $0 }

11. 类型转换

let value = optional as! String

12. 可选链

let value = optional?.uppercased()

13. for

for element in optionals {
  if let value = element {

14. for case let

for case let optional? in optionals {

15. forEach

optionals?.forEach { value in

16. 错误转换成optional

try? aThrowingCall()
try! aThrowingCall()

参考： https://www.optionals.org