easy uuid-v4 for dart

uuidv4.dart

// Ran with http://www.cryptosys.net/pki/uuid-rfc4122.html

import 'dart:math' as m;

void main() {
  for (var i = 0; i < 1000000; i++) {
    var thing = getThing();

    print(thing);
    print(thing.length);
    assert(thing.length == 36);

    assert(thing[14] == '4');

    print(thing[19]);
    assert(const ['8', '9', 'A', 'B'].contains(thing[19]));
  }
}

String getThing() {
  var rnd = new m.Random.secure();

  var bytes = new List<int>.generate(16, (_) => rnd.nextInt(256));
  bytes[6] = (bytes[6] & 0x0F) | 0x40;
  bytes[8] = (bytes[8] & 0x3f) | 0x80;

  var chars = bytes
      .map((b) => b.toRadixString(16).padLeft(2, '0'))
      .join()
      .toUpperCase();

  return '${chars.substring(0, 8)}-${chars.substring(8, 12)}-'
      '${chars.substring(12, 16)}-${chars.substring(16, 20)}-${chars.substring(20, 32)}';
}