Question

我有以下描述国家的课程：

class Country: NSObject {

    public var name: String

    static let england = Country(name: "England")
    static let scotland = Country(name: "Scotland")
    static let allCountries = [england, scotland]

    init(name: String) {
        self.name = name
        super.init()
    }

    convenience init?(named name: String) {
        guard let country = Country.allCountries.filter( { $0.name == name } ).first else { return nil }
        self.init(name: country.name)
    }

}

要获取常数Country.england，我将使用：

let england = Country.england

但是，我希望能够使用String从convenience init?(named name: String)获取此常量，如下所示：

let england = Country(named: "England")

这似乎有些笨拙，并且此代码初始化了一个新的“ england”实例，而不是采用静态实例。

是否有更快捷的方法？理想情况下，我只想在self = country函数中使用convenience init?(named name: String)，但出现错误无法赋值：“自我”是不可变的。

感谢您的帮助。

Answer 1

如果您的Country只有一个name，那么最好使用枚举…

enum Country: String, CaseIterable {
    case england = "England"
    case scotland = "Scotland"
}

Country(rawValue: "Scotland") // Optional(scotland)
Country(rawValue: "Wales")    // nil

注意CaseIterable是Swift 4.2+，但允许您编写Country.allCases

Country.allCases  // [england, scotland]

Answer 2

代之以编写named工厂方法呢？

static func named(_ name: String) -> Country? {
    return Country.allCountries.first(where: { $0.name == name } )
}

// usage:
let england = Country.named("England")!

如果Country是一个结构，则可以使用初始化方法：

struct Country {

    public var name: String

    static let england = Country(name: "England")
    static let scotland = Country(name: "Scotland")
    static let allCountries = [england, scotland]

    init(name: String) {
        self.name = name
    }

    init?(named name: String) {
        guard let country = Country.allCountries.filter( { $0.name == name } ).first else { return nil }
        self = country
    }

}

从字符串获取静态变量

2 个答案: