オプショナル型のサンプル

Optional_sample.swift

//: Playground - noun: a place where people can play

import UIKit

var strs : String? = "SOMESTRING"
print(strs!.lowercaseString)


var a: Int?
//var b: Optional<Int> // Int?　と同じ意味
a = nil //->nilが入っても大丈夫

var b: Int // 非 optional 型
//b = nil    // -> Nil cannot be assigned to type 'Int'


var unoptionalInt: Int = 1
print(unoptionalInt + 2) // -> 3

var optionalInt : Int? = 1
print(optionalInt! + 2) //Value of optional type 'Int?' not unwrapped;

//optionalInt = nil
//print(optionalInt!)
var wrappedInt: Int? = 1 // Optional 型


var optionalString : String? = "SOME_STRING"
print(optionalString?.lowercaseString)


/*オプショナルチェーイング
?を使ってつなげる。つなげるなかでnilがあったらそこですべてnilになる
optional型が変える
*/
class Room {
    var adress : String = "渋谷区"
}
class Person {
    var room : Room?
}

var aperson = Person()
aperson.room?.adress = "目黒区"
aperson.room = Room()
print(aperson.room?.adress)

if let adress = aperson.room?.adress{
    
    print(adress)
}else{
    print("住所が登録されていません")
}

while let adress = aperson.room?.adress{
    print(adress)
    break
}


//
// 自動的にアンラップされる
//
print(wrappedInt == 1) // -> true
print(wrappedInt >= 1) // -> true
print(wrappedInt >  1) // -> false
print(wrappedInt <= 1) // -> true
print(wrappedInt <  1) // -> false
print(wrappedInt != 1) // -> false

wrappedInt = nil
print(wrappedInt == 1) // -> false

var str = "Hello, playground"
let possibleNumber = "123"
let convertedNumber = Int(possibleNumber)
print(convertedNumber)

var serverResponseCode: Int? = 404
// serverResponseCode contains an actual Int value of 404
serverResponseCode = nil
// serverResponseCode now contains no value”

if convertedNumber != nil {
    print("convertedNumber has an integer value of \(convertedNumber!).")
}
// prints "convertedNumber has an integer value of 123.”


/*
オプショナルバインディング
*/
if let actualNumber = Int(possibleNumber) {
    print("\'\(possibleNumber)\' has an integer value of \(actualNumber)")
} else {
    print("\'\(possibleNumber)\' could not be converted to an integer")
}
//actualNumberは初期化されているので!でアンラップしなくてもよい


if let firstNumber = Int("4"), secondNumber = Int("42") where firstNumber < secondNumber {
print("\(firstNumber) < \(secondNumber)")
}
// prints "4 < 42”




let possibleString: String? = "An optional string."
let forcedString: String = possibleString! // requires an exclamation mark
print(forcedString)



/**implicitly unwrapped optional*/
var assumedString: String! = "An implicitly unwrapped optional string."
let implicitString: String = assumedString // no need for an exclamation mark”
print(implicitString)

/*オプショナルバインディングもできる*/
if let definiteString = assumedString {
    print(definiteString)
}




assumedString = nil
//print(assumedString) ->implicitly unwrapped optionalにnilいれるてアクセスするとランタイムエラーになる