swift(二)

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记录下今天学的东西。。看到闭包了。。看不下去了。。

let strValue1:String? = "abcd"//声明了一个Optional类型值，可能包含一个String值，也可能什么都不包含等同于 var strValue1: Optional<String>

let hasValue = strValue1?.characters.count

print("hasValue:\(hasValue)")//声明一个可选类型

let strValue2:String! = "def"//隐式拆包

let hasValue2 = strValue2.characters.count

print("hasValue:\(hasValue2)")

//使用强制拆包需要确定里面一定是非nil的值

var count :Int?

count = 100

if count !=nil {

print("count is\(String(count))")

}

//可选绑定

let possibleCount ="abc"

iflet actualNumber = Int(possibleCount) {

print("\(possibleCount) value of\(actualNumber)")

}else {

print("no value")

}

//as类型转换 is类型检查

//断言

// let age = -3

// assert(age >= 0, "This is assert")//会打印this is assert会崩

//创建一个集合

var setB =Set<String>()

setB.insert("abc")

setB.insert("def")

setB.insert("123")

print("\(setB)")

for jihein setB.sort() {

print("\(jihe)")

}

//字典

var airports: [String:String] = ["111":"a","222":"b"]

print("airports :\(airports.count)");

iflet oldValue = airports.updateValue("123456", forKey:"11") {

print("The old Value\(oldValue)")

}

for (airportCode, airportName)in airports {

print("\(airportName):\(airportCode)")

}

//swift中的fallthrough 使代码块执行继续连接到下一个case的执行代码和c的switch相同

//带标签的语句

//label name: while condition { statements }

//eg: gameLoop: while square != finalSquare {}

//使用guard执行取决于布尔值一个guard里面总代有一个else

func greet(person: [String:String]) {

guardlet name = person["name"]else {

return

}

print("Hello\(name)")

guardlet location = person["location"]else {

print("I hope the weather is nice near you")

return

}

print("I hope the weather is nice in\(location).")

}

greet(["name":"John"])

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