Swift enum枚举类型使用详解

import Foundation
public enum AFError: Error {
    /// The underlying reason the `.urlRequestValidationFailed`
    public enum URLRequestValidationFailureReason {
        /// URLRequest with GET method had body data.
        case bodyDataInGETRequest(Data)
    }
    /// `URLRequest` failed validation.
    case urlRequestValidationFailed(reason: URLRequestValidationFailureReason)
}
// MARK: - Error Descriptions
extension AFError: LocalizedError {
    public var errorDescription: String? {
        switch self {
        case .explicitlyCancelled:
            return "Request explicitly cancelled."
        case let .invalidURL(url):
            return "URL is not valid: \(url)"
        case let .parameterEncodingFailed(reason):
            return reason.localizedDescription
        case let .parameterEncoderFailed(reason):
            return reason.localizedDescription
        case let .multipartEncodingFailed(reason):
            return reason.localizedDescription
        case let .requestAdaptationFailed(error):
            return "Request adaption failed with error: \(error.localizedDescription)"
        case let .responseValidationFailed(reason):
            return reason.localizedDescription
        case let .responseSerializationFailed(reason):
            return reason.localizedDescription
        case let .requestRetryFailed(retryError, originalError):
            return """
            Request retry failed with retry error: \(retryError.localizedDescription), \
            original error: \(originalError.localizedDescription)
            """
        case .sessionDeinitialized:
            return """
            Session was invalidated without error, so it was likely deinitialized unexpectedly. \
            Be sure to retain a reference to your Session for the duration of your requests.
            """
        case let .sessionInvalidated(error):
            return "Session was invalidated with error: \(error?.localizedDescription ?? "No description.")"
        #if !(os(Linux) || os(Windows))
        case let .serverTrustEvaluationFailed(reason):
            return "Server trust evaluation failed due to reason: \(reason.localizedDescription)"
        #endif
        case let .urlRequestValidationFailed(reason):
            return "URLRequest validation failed due to reason: \(reason.localizedDescription)"
        case let .createUploadableFailed(error):
            return "Uploadable creation failed with error: \(error.localizedDescription)"
        case let .createURLRequestFailed(error):
            return "URLRequest creation failed with error: \(error.localizedDescription)"
        case let .downloadedFileMoveFailed(error, source, destination):
            return "Moving downloaded file from: \(source) to: \(destination) failed with error: \(error.localizedDescription)"
        case let .sessionTaskFailed(error):
            return "URLSessionTask failed with error: \(error.localizedDescription)"
        }
    }
}
extension AFError.URLRequestValidationFailureReason {
    var localizedDescription: String {
        switch self {
        case let .bodyDataInGETRequest(data):
            return """
            Invalid URLRequest: Requests with GET method cannot have body data:
            \(String(decoding: data, as: UTF8.self))
            """
        }
    }
}

public enum URLRequestValidationFailureReason {
    /// URLRequest with GET method had body data.
    case bodyDataInGETRequest(Data)
}

case let .urlRequestValidationFailed(reason):
    return "URLRequest validation failed due to reason: \(reason.localizedDescription)"

/// 将let放在取枚举值的地方，我个人比较喜欢这种写法
case .urlRequestValidationFailed(let reason):
/// 不关心枚举带参，用_代替
case .urlRequestValidationFailed(_):
/// 直接只显示枚举的状态，省略参数显示
case .urlRequestValidationFailed:

@frozen public enum Result<Success, Failure> where Failure : Error {
    /// A success, storing a `Success` value.
    case success(Success)
    /// A failure, storing a `Failure` value.
    case failure(Failure)
    /// 其他的内容我省略了
}

typealias Callback<Success, SomeError: Error> = (Success?, SomeError?) -> Void

typealias ResultCallback<Success, SomeError: Error> = (Result<Success, SomeError>) -> Void

@frozen public enum Optional<Wrapped> : ExpressibleByNilLiteral {
    /// The absence of a value.
    ///
    /// In code, the absence of a value is typically written using the `nil`
    /// literal rather than the explicit `.none` enumeration case.
    case none
    /// The presence of a value, stored as `Wrapped`.
    case some(Wrapped)
}

enum NumberType: String {
    case one, two, three, four, five
}
let s: NumberType = .one
print(s.rawValue)

enum NumberValue: Int {
    case one = 3, two, three, four, five
}