字典是一种存储相同类型多重数据的存储器。每个值（value）都关联独特的键（key），键作为字典中的这个值数据的标识符。和数组中的数据项不同，字典中的数据项并没有具体顺序。

　　字典写作Dictionary<Key, Value>。也可以写作[Key: Value]

 

　　创建空字典

var namesOfIntegers = [Int: String]() // namesOfIntegers is an empty [Int: String] dictionary

 

　　类型推断写作[:]

namesOfIntegers[16] = "sixteen" // namesOfIntegers now contains 1 key-value pair namesOfIntegers = [:] // namesOfIntegers is once again an empty dictionary of type [Int: String]

 

 

　　创建字典字面量

[key 1: value 1, key 2: value 2, key 3: value 3]

var airports: [String: String] = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]

 

　　类型推断写作

var airports = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]

 

 

　　访问和修改

　　count返回字典的键值对数

　　isEmpty判断字典是否为空

　　

airports["LHR"] = "London Heathrow

 

 

if let oldValue = airports.updateva lue("Dublin Airport", forKey: "DUB") { print("The old value for DUB was \(oldValue).") } // Prints "The old value for DUB was Dublin.

 

 

　　removeva lueForKey(_:)删除键值对  

if let removedValue = airports.removeva lueForKey("DUB") { print("The removed airport's name is \(removedValue).") } else { print("The airports dictionary does not contain a value for DUB.") } // Prints "The removed airport's name is Dublin Airport.

 

 

 遍历

for (airportCode, airportName) in airports { print("\(airportCode): \(airportName)") } // YYZ: Toronto Pearson // LHR: London Heathrow

 

 

for airportCode in airports.keys { print("Airport code: \(airportCode)") } // Airport code: YYZ // Airport code: LHR for airportName in airports.values { print("Airport name: \(airportName)") } // Airport name: Toronto Pearson // Airport name: London Heathrow