映射一个struct数组

Question

我有一个包含几个字段的struct数组.我想映射数组以创建另一个包含字段子集的struct

struct History: {
   let field1: String
   let field2: String
   let field3: String
   let field4: String
}

struct SubHistory: {
   let field1: String
   let field2: String
}

我可以使用for in循环.但是有可能使用地图,不是吗？

Answer 1

是的,您可以通过map以下方式使用:

let histories: [History] // array of History structs
let subHistories = histories.map { SubHistory(field1: $0.field1, field2: $0.field2) }

Answer 2

As a slight variation of kiwisip's correct answer: I would suggest to put the logic of “creating a SubHistory from a History” into a custom initializer:

extension SubHistory {
    init(history: History) {
        self.init(field1: history.field1, field2: history.field2)
    }
}

Then the mapping can be simply done as

let histories: [History] = ...
let subHistories = histories.map(SubHistory.init)

将初始化程序放入扩展中具有以下优点：默认的逐成员初始化程序仍然可以合成–此观察的属性归@kiwisip！