2、Swift 4 与 Foundation 框架新特性深度解析

Swift 4 与 Foundation 框架新特性深度解析

1. Swift 4 中 Dictionary 的增强特性

1.1 基于序列的初始化器

Swift 4 允许从键值对序列创建字典。例如，可以创建一个编号的商品列表：

let groceries = Dictionary(uniqueKeysWithValues: zip( 
  1..., 
  ["Prosciutto", "Heavy Cream", "Butter", "Parmesan",  
   "Small shells"]) 
) 
// [5: "Small shells", 2: "Heavy Cream", 3: "Butter",  
//  1: "Prosciutto", 4: "Parmesan"]

如果已有元组流，也能进行创建：

let housePointTotals = [("Slytherin", 472),  
                        ("Ravenclaw", 426),  
                        ("Hufflepuff", 352),  
                        ("Gryffindor", 312)] 
let banquetBegins = Dictionary( 
      uniqueKeysWithValues: housePointTotals) 
// ["Ravenclaw": 426, "Hufflep