errors.swift

import Cocoa

public enum TagErrors: LocalizedError, CaseIterable {
  case InvalidCallingConvention

  var localizedDescription: String {
    switch self {
    case .InvalidCallingConvention: return "A closure was called with an invalid calling convention, probably (nil, nil)"
    }
  }
}

func test() throws -> String {
//  throw TagErrors.InvalidCallingConvention
  throw NSError(domain: "test", code: 0)
}

func otherThrows() throws {
  do {
    _ = try test()
  } catch let error as TagErrors {
    print("Got a TagErrror \(error.localizedDescription)")
  }
}

func otherExhaustive() {
  do {
    _ = try test()
  } catch let error as TagErrors {
    print("Got a TagErrror \(error.localizedDescription)")
  } catch {
    print("Some other error that I will ignore")
  }
}


func otherWithoutThrowAndNotExhaustive() {
  do {
    _ = try test() // Compiler Error: Errors thrown from here are not handled because the enclosing catch is not exhaustive
  } catch let error as TagErrors {
    print("Got a TagErrror \(error.localizedDescription)")
  }
}

do {
  try otherThrows()
} catch let localError {
  print("other() threw: \(localError)")
}

otherExhaustive()
otherWithoutThrowAndNotExhaustive()