hello.swift

#!/usr/bin/env xcrun swift

protocol SomeType { }

extension SomeType {
  func maybeGreeting(noReally: Bool) -> String? {
    return (noReally ? "howzit" : nil)
  }
}

protocol BaseError { }
extension BaseError { 
  // minimum requirements to conform to ErrorType
  var _domain : String  { return "theDomain" }
  var _code : Int       { return 12 }
}

struct MyError : ErrorType, BaseError { }
struct MyOtherError : ErrorType, BaseError { }

struct MyThing : SomeType {
  func greet(shouldThrow: Bool) throws { 
    defer { print("deferred 1") }
    if let unwrappedGreeting = maybeGreeting(shouldThrow) {
      print(unwrappedGreeting) 
      throw MyOtherError()
    } else {
      defer { print("deferred 2") }
      throw MyError()
    }
  }
}

do {
  let shouldThrow = true
  try MyThing().greet(shouldThrow)
} catch is MyError {
  print("caught myerror")
} catch is MyOtherError {
  print("caught myothererror")
}