swift - Swift 中非文字值的枚举

Question

有什么方法可以将非文字值(如字典的元组)映射到枚举？以下代码将抛出 Raw value for enum must be literal。

enum FileType {
    case VIDEO = ["name": "Video", "contentTypeMatcher": "video/"]
    case IMAGE = ["name": "Image", "contentTypeMatcher": "image/"]
    case AUDIO = ["name": "Audio", "contentTypeMatcher": "aduio/"]
    case PDF   = ["name": "PDF", "contentTypeMatcher":"application/pdf"]
    case TEXT  = ["name": "Text", "contentTypeMatcher": "text/"]
    case FOLDER= ["name": "Folder", "contentTypeMatcher" :"application/x-directory"]
    case PLAIN = ["name": "Plain", "contentTypeMatcher": ""]
}

当我使用元组时也是一样的:

enum FileType {
    case VIDEO  = (name: "Video", contentTypeMatcher: "video/")
    case IMAGE  = (name: "Image", contentTypeMatcher: "image/")
    case AUDIO  = (name: "Audio", contentTypeMatcher: "aduio/")
    case PDF    = (name: "PDF", contentTypeMatcher:"application/pdf")
    case TEXT   = (name: "Text", contentTypeMatcher: "text/")
    case FOLDER = (name: "Folder", contentTypeMatcher :"application/x-directory")
    case PLAIN  = (name: "Plain", contentTypeMatcher: "")
}

Answer 1

@Antonio 给出了解决方法，但没有回答实际问题。

定义你的枚举。

enum FileType {

    case Image, Video
}

为案例提供非文字值，无论您想要什么类型，都符合 RawRepresentable 协议(protocol)。通过枚举扩展来实现更简洁的代码。

extension FileType: RawRepresentable {

    typealias Tuple = (name: String, contentTypeMatcher: String)

    private static let allCases = [FileType.Image, .Video]

    // MARK: RawRepresentable

    typealias RawValue = Tuple

    init?(rawValue: Tuple) {

        guard let c = { () -> FileType? in

            for iCase in FileType.allCases {
                if rawValue == iCase.rawValue {
                    return iCase
                }
            }
            return nil

        }() else { return nil }
        self = c
    }

    var rawValue: Tuple {

        switch self {
        case .Image: return Tuple("Image", "image/")
        case .Video: return Tuple("Video", "video/")
        }
    }
}

为了能够在 switch 中匹配 Tuple，实现模式匹配运算符。

private func ~= (lhs: FileType.Tuple, rhs: FileType.Tuple) -> Bool {

    return lhs.contentTypeMatcher == rhs.contentTypeMatcher && lhs.name == rhs.name
}

就是这样......

let a = FileType.Image
print(a.rawValue.name) // "Image"
let b = FileType(rawValue: a.rawValue)!
print(a == b) // "true"
print(b.rawValue.contentTypeMatcher) // "image/"

假设我没有提问就回答了问题。现在......枚举(至少在 Swift 中)被设计成具有独特的案例。需要注意的是，您可以(我希望是偶然的)在更多情况下保持相同的 rawValue 。一般来说，你的示例代码让我闻起来。除非您(出于非常合理的原因)需要从元组创建新的枚举值，否则请考虑重新设计。如果您想使用此解决方法，我建议(取决于项目)实现一些检查是否所有案例原始值都是唯一的。如果没有，考虑一下:

enum FileType {

    case Video, Image

    var name: String {
        switch self {
        case .Image: return "Image"
        case .Video: return "Video"
    }

    var contentTypeMatcher: String {
        switch self {
        case .Image: return "image/"
        case .Video: return "video/"
    }
}