ios - 集合中项目的顺序已更改，Set，Swift

Question

我正在创建 2 个包含 String 的集合，如下所示

 let set1 : Set<String>   =   (["07:00", "QShift", "PRN"])
 let set2 : Set<String>   =   (["07:15", "QShift", "PRN"])

起初，我认为每个集合中字符串的顺序将与它们添加时的顺序完全相同。但是我对 set1 中的一个是错误的，控制台给了我这个

Printing description of set1:
▿ 3 elements
  - [0] : "QShift"
  - [1] : "PRN"
  - [2] : "07:00" { ... }

Printing description of set2:
▿ 3 elements
  - [0] : "07:15"
  - [1] : "QShift"
  - [2] : "PRN" { ... }

有谁知道为什么 set1 中的字符串顺序已更改为 QShift, PRN, 07:00？

Answer 1

因为Set是一个无序的数据结构。

Set引用:

A set stores distinct values of the same type in a collection with no defined ordering. You can use a set instead of an array when the order of items is not important, or when you need to ensure that an item only appears once.

你应该看看NSOrderedSet类引用，更多 API:

NSOrderedSet and its subclass, NSMutableOrderedSet, declare the programmatic interfaces to an ordered collection of objects.