好的。很简单。不需要CodingKeys：

enum EmailVerificationStatus: String, Codable {
    case verified = "VERIFIED"
    case unverified = "UNVERIFIED"
}

我通常是这么做的：

struct EmailVerificationStatus: String, Codable {
    var unverified: String
    var verified: String

    enum CodingKeys: String, CodingKey {
        case unverified = "UNVERIFIED"
        case verified = "VERIFIED"
    }
}

我建议你使用struct作为Email...类型，并将枚举CodingKeys嵌套在你的struct中。CodingKeys允许你将你的struct变量Map到你的源数据案例（来自webservice）。

struct EmailVerificationStatus: String, Codable {
        var unverified: String
        var verified: String

        enum CodingKeys: String, CodingKey {
            case unverified = "UNVERIFIED"
            case verified = "VERIFIED"
        }
    }

当枚举具有关联值时，另一个可能的解决方案是将Codable兼容性放入扩展中，这样它就不会抱怨您实现了CodingKeys枚举。
大概是这样的

enum EmailVerificationStatus: String {
    case unverified
    case verified(email:String)
}

extension EmailVerificationStatus: Codable {
  enum CodingKeys: String, CodingKey {
    case unverified = "UNVERIFIED"
    case verified = "VERIFIED"
  }
}