看看这个很酷的版本。其思想是同时实现String和ErrorType协议，并使用错误的rawValue。

enum UserValidationError: String, Error {
  case noFirstNameProvided = "Please insert your first name."
  case noLastNameProvided = "Please insert your last name."
  case noAgeProvided = "Please insert your age."
  case noEmailProvided = "Please insert your email."
}

用法:

do {
  try User.define(firstName,
                  lastName: lastName,
                  age: age,
                  email: email,
                  gender: gender,
                  location: location,
                  phone: phone)
}
catch let error as User.UserValidationError {
  print(error.rawValue)
  return
}

最简单的解决方案，没有额外的扩展，枚举，类等:

NSException(name:NSExceptionName(rawValue: "name"), reason:"reason", userInfo:nil).raise()

抛出代码应该清楚错误消息是适合显示给最终用户还是仅用于开发人员调试。为了表明描述可以显示给用户，我使用了实现LocalizedError协议的struct DisplayableError。

struct DisplayableError: Error, LocalizedError {
    let errorDescription: String?

    init(_ description: String) {
        errorDescription = description
    }
}

投掷用途:

throw DisplayableError("Out of pixie dust.")

显示用途:

let messageToDisplay = error.localizedDescription

我喜欢@Alexander-Borisenko的回答，但是当被捕捉为错误时，本地化的描述没有返回。看起来你需要使用LocalizedError代替:

struct RuntimeError: LocalizedError
{
    let message: String

    init(_ message: String)
    {
        self.message = message
    }

    public var errorDescription: String?
    {
        return message
    }
}

更多细节请看这个答案。

如果你不需要捕捉错误，你想立即停止应用程序，你可以使用一个fatalError: fatalError("自定义消息在这里")

看看这个很酷的版本。其思想是同时实现String和ErrorType协议，并使用错误的rawValue。

enum UserValidationError: String, Error {
  case noFirstNameProvided = "Please insert your first name."
  case noLastNameProvided = "Please insert your last name."
  case noAgeProvided = "Please insert your age."
  case noEmailProvided = "Please insert your email."
}

用法:

do {
  try User.define(firstName,
                  lastName: lastName,
                  age: age,
                  email: email,
                  gender: gender,
                  location: location,
                  phone: phone)
}
catch let error as User.UserValidationError {
  print(error.rawValue)
  return
}