代碼: 選擇全部
var canBeNil1 : Int? = 4
print("canBeNil1 : \(canBeNil1!)") // unwrap it. return 4
canBeNil1 = nil
print("canBeNil1 : \(canBeNil1)") // return nil
// print("canBeNil1 : \(canBeNil1!)") // fatal error: unexpectedly found nil while unwrapping an Optional value
// automatically unwrap
let canBeNil2: Int! = 4
print("canBeNil2 : \(canBeNil2!)") // return 4
let canBeNil3: Int! = nil
print("canBeNil3 : \(canBeNil3?.toIntMax())") // return nil, ignore toIntMax()
// print("canBeNil3 : \(canBeNil3!.toIntMax())") // fatal error: unexpectedly found nil while unwrapping an Optional value
// let maxInt = canBeNil3.toIntMax() // fatal error: unexpectedly found nil while unwrapping an Optional value
// print("maxInt : \(maxInt)")
if let maxInt = canBeNil3?.toIntMax() // if canBeNil3 is null then run else
{
print("maxInt : \(maxInt)")
}
else
{
print("maxInt : 0")
}
let stringBeNil1: String? = "abc"
print("stringBeNil1 : \(stringBeNil1)") // return Optional("abc")
if let newString = stringBeNil1
{
print("newString : \(newString)") // return abc
}
var stringBeNil2: String! = "abc"
print("stringBeNil2 : \(stringBeNil2)") // return abc
stringBeNil2 = nil
print("stringBeNil2 : \(stringBeNil2)") // return nil