如何从 String 和 String 初始化字典？

Question

我的具体任务是创建一个可失败的初始化程序，它接受字典作为参数并初始化结构的所有存储属性。键应该是 "title"、"author"、"price" 和 "pubDate"。

struct Book {
    let title: String
    let author: String
    let price: String?
    let pubDate: String?

我只是不确定在这里做什么。我走了几条不同的路，阅读了有关字典和初始化程序的文档，但没有任何运气。我主要不确定如何为 init 方法设置参数。这是我的（抽象）想法

init?([dict: ["title": String], ["author": String], ["price": String], ["pubDate": String]]) {
        self.title = dict["title"]
        self.author = dict["author"]
        self.price = dict["price"]
        self.pubDate = dict["pubDate"]
    }

我错过了什么？

Answer 1

试试这个：

struct Book {
    let title: String
    let author: String
    let price: String?
    let pubDate: String?

    init?(dict: [String: String]) {
        guard dict["title"] != nil && dict["author"] != nil else {
            // A book must have title and author. If not, fail by returning nil
            return nil
        }

        self.title = dict["title"]!
        self.author = dict["author"]!
        self.price = dict["price"]
        self.pubDate = dict["pubDate"]
    }
}

// Usage:
let book1 = Book(dict: ["title": "Harry Potter", "author": "JK Rowling"])
let book2 = Book(dict: ["title": "Harry Potter", "author": "JK Rowling", "price": ""])
let book3 = Book(dict: ["title": "A book with no author"]) // nil

这表示一本书必须有 author 和 title。如果两者都没有，它将失败。 price 和 pubDate 是可选的。

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