Swift program to print out all the unicode scalars in a Foundation CharacterSet.

scalars.swift

// Prints out all the unicode scalars in a Foundation CharacterSet.
//
// Compile: swiftc -O scalars.swift
// Run: ./scalars <character set name>

import Foundation

extension UnicodeScalar {
  static var allScalars: AnySequence<UnicodeScalar> {
    let numbers = sequence(first: 0, next: { $0 + 1 })
    let scalars = numbers
        .lazy
        .prefix(while: { $0 < 0xFFFF })
        .flatMap(UnicodeScalar.init)

    return AnySequence(scalars)
  }
}

extension CharacterSet {
  static func named(_ string: String) -> CharacterSet? {
    let name = string
      .replacingOccurrences(of: "Characters$", with: "CharacterSet", options: .regularExpression)
      .replacingOccurrences(of: "s$", with: "CharacterSet", options: .regularExpression)

    let klass = NSCharacterSet.self as AnyObject
    let selector = Selector(name)
    guard klass.responds(to: selector) else { return nil }
    return (klass.perform(selector).takeUnretainedValue() as! CharacterSet)
  }
}

func usage(_ message: String) -> Never {
  fail(
    "\(message)\n"
    + "\n"
    + "See the 'Type Properties' section of https://developer.apple.com/reference/foundation/characterset\n"
    + "for a list of character set names."
  )
}

func fail(_ message: String) -> Never {
  fputs("\(message)\n", stderr)
  exit(1)
}

guard case let arguments = CommandLine.arguments.dropFirst(),
  let characterSetName = arguments.first
  else { usage("Please specify a character set name.") }

guard let characterSet = CharacterSet.named(characterSetName)
  else { usage("No character set found with name '\(characterSetName)'.") }

for scalar in UnicodeScalar.allScalars where characterSet.contains(scalar) {
  print(scalar, terminator: "")
}

print()