1、字典写法

Dictionary<KeyType,ValueType>,KeyType是你想要储存的键，ValueType是你想要储存的值。

唯一的限制就是KeyType必须是可哈希的，就是提供一个形式让它们自身是独立识别的

Swift的全部基础类型都能够

2、创建字典

var airport :Dictionary<String, String> = ["TYO": "Tokyo", "DUB": “Dublin"]

var namesOfIntegers = Dictionary<Int, String>()

namesOfIntegers[16] = "sixteen"

3、字典元素个数

airports.count

airports["LHR"] = "London"

airports["LHR"] = "London Heathrow"

updateValue(forKey:) 方法返回一个和字典的值同样类型的可选值. 
比如，假设字典的值的类型时String，则会返回String? 或者叫“可选String“，这个可选值包括一个假设值发生更新的旧值和假设值不存在的nil值。        
if let oldValue = airports.updateValue("Dublin International", forKey: "DUB") {
println("The old value for DUB was \(oldValue).")
}

let airportName = airports["DUB"]

7、移除key相应的值

airports["APL"] = "Apple International"
// "Apple International" 不是 APL的真实机场,所以删除它
airports["APL"] = nil

从一个字典中移除一个键值对能够使用removeValueForKey方法，这种方法假设存在键所相应的值，则移除一个键值对，并返回被移除的值，否则返回nil。
let removedValue = airports.removeValueForKey("DUB")

for (airportCode, airportName) in airports {
println("\(airportCode): \(airportName)")
}

for airportCode in airports.keys {
println("Airport code: \(airportCode)")
}
// Airport code: TYO
// Airport code: LHR
for airportName in airports.values {
println("Airport name: \(airportName)")
}

let airportCodes = Array(airports.keys)
let airportNames = Array(airports.values)