Swift 学习笔记

感谢Github上The Swift Programming Language开源翻译的中文版，感谢极客学院wiki提供的PDF版本
SwiftTour是对Swift主要的语言特性有个速览，后续的教程会逐个展开阐述。
代码上传至Github，有兴趣的可以下载下来试试

import UIKit

var str = "Hello,World!"

print(str)

// 变量用var声明，常量用let声明，变量类型自动推断
// 可在变量后声明类型，用冒号分隔
var myVariable = 42
let myConstant = 42
myVariable = 50
let explictDouble: Double = 60

// 值永远不会被隐式转换为其他类型，需要转换必须采用显式转换
let label = "The width is "
let width = 94
let widthLabel = label + String(width)

更为常见的将值转换为字符串的方法

let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples"
let fruitSummary = "I have \(apples + oranges) pieces of fruit"

[]用来创建数组或字典

var shoppingList = ["catfish","water","tulips","blue paint"]
shoppingList[1]  = "bottle of water"

var occupations = [
    "Malcolm": "Captain","Kaylee": "Mechanic"
]
occupations["Jayne"] = "Public Relations"

创建一个空数组或者字典

let emptyArray1 = [String]()
let emptyDictionary1 = [String: Float]()
let emptyArray2: [String] = []
let emptyDictionary2: [String: Float] = [:]

控制流，if和switch用于选择，for-in,for,while和repeat-while用于循环

let individualscores = [75,43,103,87,12]
var teamscore = 0
for score in individualscores {
    if score > 50 {
        teamscore += 3
    } else {
        teamscore += 1
    }
}
print(teamscore)

隐式

// 由于不支持隐式转换，条件必须是一个布尔表达式
// 一般采用可选值配合if和let，处理值缺失判断
var optionalString: String? = "Hello"
print(optionalString == nil)
var optionalName: String? = "John Appleseed"
var greeting = "Hello"
if let name = optionalName {
    greeting = "Hello,\(name)"
}

Switch支持任意类型的数据以及各种比较操作

let vegetable = "red pepper"

switch vegetable {
case "celery" :
    print("Add some raisins and make ants on a log")
case "cucumber","watercress" :
    print("That woould make a good tea sandwich")
case let x where x.hasSuffix("pepper") :
    print("Is it a spicy \(x)?")
default :
    print("Everything tastes good in soup")
}

使用for-in遍历字典

// 使用for-in遍历字典
let interestingNumbers = [
    "Prime": [2,3,5,7,11,13],"Fibonacci": [1,1,2,8],"Square": [1,4,9,16,25],]
var largest = 0
var numberGroup: String = "Null"
for (kind,numbers) in interestingNumbers {
    for number in numbers {
        if number > largest {
            largest = number
            numberGroup = kind
        }
    }
}
print(numberGroup,largest)

while循环

// while循环
var n = 2
while n < 100 {
    n = n * 2
}
print(n)

var m = 2
repeat {
    m = m * 2
} while m < 100
print(m)

可以在循环中使用..<来表示范围,包含上界使用…

var firstForLoop = 0
for i in 0..<4 {
    firstForLoop += i
}
print(firstForLoop)

var secondForLoop = 0
for var i = 0; i < 4; ++i {
    secondForLoop += i
}
print(secondForLoop)