集合类型

Swift 语言提供 Arrays、Sets 和 Dictionaries 三种基本的集合类型用来存储集合数据。

• 数组（Arrays）是有序数据的集。
• 集合（Sets）是无序无重复数据的集。

• 字典（Dictionaries）是无序的键值对的集。

  
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数组：
var someInts = [Int]()   //初始化数组
var someInts: [Int] = []
var shoppingList: [String] = ["Eggs", "Milk"]  //推荐该方式

集合：
var letters = Set<Character>()
letters.insert("a")

//用数组字面量创建集合
var favoriteGenres: Set<String> = ["Rock", "Classical", "Hip hop"]

字典：
var namesOfIntegers = [Int: String]()
var airports: [String: String] = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]

//字典遍历
for (airportCode, airportName) in airports {
    print("\(airportCode): \(airportName)")
}
for airportCode in airports.keys {
    print("Airport code: \(airportCode)")
}
// Airport code: YYZ
// Airport code: LHR
for airportName in airports.values {
    print("Airport name: \(airportName)")
}