Swift: Switch on Regex! Aggregated from http://www.lesstroud.com/swift-using-regex-in-switch-statements/ and http://nshipster.com/swift-literal-convertible/

Regex.swift

struct Regex {
  let pattern: String
  let options: NSRegularExpressionOptions
  
  private var matcher: NSRegularExpression {
    return try! NSRegularExpression(pattern: pattern, options: options)
  }
  
  init(pattern: String, options: NSRegularExpressionOptions! = nil)
  {
    self.pattern = pattern
    self.options = options ?? []
  }
  
  func match(string: String, options: NSMatchingOptions = []) -> Bool
  {
    let entireRange = NSMakeRange(0, string.characters.count)
    let matches = matcher.numberOfMatchesInString(string, options: options, range: entireRange)
    return matches > 0
  }
}

protocol RegularExpressionMatchable {
  func match(regex: Regex) -> Bool
}

extension String: RegularExpressionMatchable {
  func match(regex: Regex) -> Bool {
    return regex.match(self)
  }
}

func ~=<T: RegularExpressionMatchable>(pattern: Regex, matchable: T) -> Bool {
  return matchable.match(pattern)
}

// That's it! Have fun using it like so:
switch inputString {
case Regex(pattern: "^4[0-9]{12}(?:[0-9]{3})?$"):
  print("It's a Visa card")
case Regex(pattern: "^3[47][0-9]{13}$"):
  print("It's American Express")
case Regex(pattern: "^5[1-5][0-9]{14}$"):
  print("It's a MasterCard")
case Regex(pattern: "^6(?:011|5[0-9]{2})[0-9]{12}$"):
  print("It's a Discover card")
default:
  print("ERROR: Unknown card type")
}

switch inputString {
case Regex(pattern: "^clemson(\\su.+)?$", options: NSRegularExpressionOptions.CaseInsensitive):
  print("GREAT School!!  Awesome Team!")
case Regex(pattern: "^(u.+)?south carolina$", options: NSRegularExpressionOptions.CaseInsensitive):
  print("I'm sorry.")
default:
  print("Bless your heart.")
}

// Just note that switch cases only execute the first branch that's matched
// The string "heyyo" matches both regular expressions, but only the first branch is executed
switch "heyyo" {
case Regex(pattern: "o$"):
  print("ends with o")
case Regex(pattern: "^h"):
  print("starts with h")
default:
  break
}