Specialized errors

playground.swift

import UIKit

// Specialized error type
public protocol CommandError: ErrorType {}

// A command that does not have specialized errors
public enum NoCommandError: CommandError {}

// The "Authorize" method returns errors
public enum AuthorizeError: CommandError {
    case WrongAuthorizeCode
    case WrongRequestId
}

// The errors the client can return
public enum ClientError<T: CommandError>: ErrorType {
    case Deserialization
    case Networking(internalError: NSError)
    case CommandError(commandError: T)
    case Unknown
}

// For any method that does not return specialized errors
public typealias ClientErrorDefault = ClientError<NoCommandError>

func testAuthorize() -> ClientError<AuthorizeError> {
    return ClientError.CommandError(commandError: AuthorizeError.WrongAuthorizeCode)
}

func testOther() -> ClientErrorDefault {
    return ClientError.Deserialization
}

func matchError() {
    let error = testAuthorize()
//    let error = testOther()

    switch error {
    case .Deserialization: print("Deserialization")
    case .Networking(let e): print("Networking: \(e)")
    case .Unknown: print("Unknown")
    case .CommandError(let e): print(e)
    }
}

matchError()