0x00 Lesson

Sometimes functions ​​fail​​​ because they have bad input, or because something went wrong internally. Swift lets us ​​throw​​ errors from functions by marking them as ​​throws​​​ before their return type, then using the ​​throw​​ keyword when something goes wrong.

First we need to define an ​​enum​​​ that describes the errors we can throw. These must always be based on Swift’s existing ​​Error​​ type. We’re going to write a function that checks whether a password is good, so we’ll throw an error if the user tries an obvious password:

enum PasswordError: Error {
  case obvious
}

Now we’ll write a ​​checkPassword()​​​ function that will throw that error if something goes wrong. This means using the throws keyword before the function’s return value, then using ​​throw PasswordError.obvious​​ if their password is “password”.

Here’s that in Swift:

func checkPassword(password: String) throws -> Bool {
  if password == "password" {
    throw PasswordError.obvious
  }
  return true
}

0x01 我的小作品

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