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intl/lib/src/intl/date_format.dart

Index: intl/lib/src/intl/date_format.dart
diff --git a/intl/lib/src/intl/date_format.dart b/intl/lib/src/intl/date_format.dart
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-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-part of intl;
-
-// TODO(efortuna): Customized pattern system -- suggested by i18n needs
-// feedback on appropriateness.
-/**
- * DateFormat is for formatting and parsing dates in a locale-sensitive
- * manner.
- *
- * It allows the user to choose from a set of standard date time formats as well
- * as specify a customized pattern under certain locales. Date elements that
- * vary across locales include month name, week name, field order, etc.
- * We also allow the user to use any customized pattern to parse or format
- * date-time strings under certain locales. Date elements that vary across
- * locales include month name, weekname, field, order, etc.
- *
- * Formatting dates in the default "en_US" format does not require any
- * initialization. e.g.
- *       print(new DateFormat.yMMMd().format(new Date.now()));
- *
- * But for other locales, the formatting data for the locale must be
- * obtained. This can currently be done
- * in one of three ways, determined by which library you import. In all cases,
- * the "initializeDateFormatting" method must be called and will return a future
- * that is complete once the locale data is available. The result of the future
- * isn't important, but the data for that locale is available to the date
- * formatting and parsing once it completes.
- *
- * The easiest option is that the data may be available locally, imported in a
- * library that contains data for all the locales.
- *       import 'package:intl/date_symbol_data_local.dart';
- *       initializeDateFormatting("fr_FR", null).then((_) => runMyCode());
- *
- * If we are running outside of a browser, we may want to read the data
- * from files in the file system.
- *       import 'package:intl/date_symbol_data_file.dart';
- *       initializeDateFormatting("de_DE", null).then((_) => runMyCode());
- *
- * If we are running in a browser, we may want to read the data from the
- * server using the XmlHttpRequest mechanism.
- *       import 'package:intl/date_symbol_data_http_request.dart';
- *       initializeDateFormatting("pt_BR", null).then((_) => runMyCode());
- *
- * The code in example/basic/basic_example.dart shows a full example of
- * using this mechanism.
- *
- * Once we have the locale data, we need to specify the particular format.
- * This library uses the ICU/JDK date/time pattern specification both for
- * complete format specifications and also the abbreviated "skeleton" form
- * which can also adapt to different locales and is preferred where available.
- *
- * Skeletons: These can be specified either as the ICU constant name or as the
- * skeleton to which it resolves. The supported set of skeletons is as follows.
- * For each skeleton there is a named constructor that can be used to create it.
- * It's also possible to pass the skeleton as a string, but the constructor
- * is preferred.
- * 
- *      ICU Name                   Skeleton
- *      --------                   --------
- *      DAY                          d
- *      ABBR_WEEKDAY                 E
- *      WEEKDAY                      EEEE
- *      ABBR_STANDALONE_MONTH        LLL
- *      STANDALONE_MONTH             LLLL
- *      NUM_MONTH                    M
- *      NUM_MONTH_DAY                Md
- *      NUM_MONTH_WEEKDAY_DAY        MEd
- *      ABBR_MONTH                   MMM
- *      ABBR_MONTH_DAY               MMMd
- *      ABBR_MONTH_WEEKDAY_DAY       MMMEd
- *      MONTH                        MMMM
- *      MONTH_DAY                    MMMMd
- *      MONTH_WEEKDAY_DAY            MMMMEEEEd
- *      ABBR_QUARTER                 QQQ
- *      QUARTER                      QQQQ
- *      YEAR                         y
- *      YEAR_NUM_MONTH               yM
- *      YEAR_NUM_MONTH_DAY           yMd
- *      YEAR_NUM_MONTH_WEEKDAY_DAY   yMEd
- *      YEAR_ABBR_MONTH              yMMM
- *      YEAR_ABBR_MONTH_DAY          yMMMd
- *      YEAR_ABBR_MONTH_WEEKDAY_DAY  yMMMEd
- *      YEAR_MONTH                   yMMMM
- *      YEAR_MONTH_DAY               yMMMMd
- *      YEAR_MONTH_WEEKDAY_DAY       yMMMMEEEEd
- *      YEAR_ABBR_QUARTER            yQQQ
- *      YEAR_QUARTER                 yQQQQ
- *      HOUR24                       H
- *      HOUR24_MINUTE                Hm
- *      HOUR24_MINUTE_SECOND         Hms
- *      HOUR                         j
- *      HOUR_MINUTE                  jm
- *      HOUR_MINUTE_SECOND           jms
- *      HOUR_MINUTE_GENERIC_TZ       jmv
- *      HOUR_MINUTE_TZ               jmz
- *      HOUR_GENERIC_TZ              jv
- *      HOUR_TZ                      jz
- *      MINUTE                       m
- *      MINUTE_SECOND                ms
- *      SECOND                       s
- *
- * Examples Using the US Locale:
- *
- *      Pattern                           Result
- *      ----------------                  -------
- *      new DateFormat.yMd()             -> 7/10/1996
- *      new DateFormat("yMd")            -> 7/10/1996
- *      new DateFormat.yMMMMd("en_US")   -> July 10, 1996
- *      new DateFormat.jm()              -> 5:08 PM
- *      new DateFormat.yMd().add_jm()    -> 7/10/1996 5:08 PM
- *      new DateFormat.Hm()              -> 17:08 // force 24 hour time
- *
- * Explicit Pattern Syntax: Formats can also be specified with a pattern string.
- * This can be used for formats that don't have a skeleton available, but these
- * will not adapt to different locales. For example, in an explicit pattern the 
- * letters "H" and "h" are available for 24 hour and 12 hour time formats 
- * respectively. But there isn't a way in an explicit pattern to get the
- * behaviour of the "j" skeleton, which prints 24 hour or 12 hour time according
- * to the conventions of the locale, and also includes am/pm markers where 
- * appropriate. So it is preferable to use the skeletons.
- *
- * The following characters are available in explicit patterns:
- *
- *     Symbol   Meaning                Presentation        Example
- *     ------   -------                ------------        -------
- *     G        era designator         (Text)              AD
- *     y        year                   (Number)            1996
- *     M        month in year          (Text & Number)     July & 07
- *     L        standalone month       (Text & Number)     July & 07
- *     d        day in month           (Number)            10
- *     c        standalone day         (Number)            10
- *     h        hour in am/pm (1~12)   (Number)            12
- *     H        hour in day (0~23)     (Number)            0
- *     m        minute in hour         (Number)            30
- *     s        second in minute       (Number)            55
- *     S        fractional second      (Number)            978
- *     E        day of week            (Text)              Tuesday
- *     D        day in year            (Number)            189
- *     a        am/pm marker           (Text)              PM
- *     k        hour in day (1~24)     (Number)            24
- *     K        hour in am/pm (0~11)   (Number)            0
- *     z        time zone              (Text)              Pacific Standard Time
- *     Z        time zone (RFC 822)    (Number)            -0800
- *     v        time zone (generic)    (Text)              Pacific Time
- *     Q        quarter                (Text)              Q3
- *     '        escape for text        (Delimiter)         'Date='
- *     ''       single quote           (Literal)           'o''clock'
- *
- * The count of pattern letters determine the format.
- *
- * **Text**:
- * * 5 pattern letters--use narrow form for standalone. Otherwise does not apply
- * * 4 or more pattern letters--use full form,
- * * 3 pattern letters--use short or abbreviated form if one exists
- * * less than 3--use numeric form if one exists
- *
- * **Number**: the minimum number of digits. Shorter numbers are zero-padded to
- * this amount (e.g. if "m" produces "6", "mm" produces "06"). Year is handled
- * specially; that is, if the count of 'y' is 2, the Year will be truncated to
- * 2 digits. (e.g., if "yyyy" produces "1997", "yy" produces "97".) Unlike other
- * fields, fractional seconds are padded on the right with zero.
- *
- * **(Text & Number)**: 3 or over, use text, otherwise use number.
- *
- * Any characters not in the pattern will be treated as quoted text. For
- * instance, characters like ':', '.', ' ', '#' and '@' will appear in the
- * resulting text even though they are not enclosed in single quotes. In our
- * current pattern usage, not all letters have meanings. But those unused
- * letters are strongly discouraged to be used as quoted text without quotes,
- * because we may use other letters as pattern characters in the future.
- *
- * Examples Using the US Locale:
- *
- *     Format Pattern                     Result
- *     --------------                     -------
- *     "yyyy.MM.dd G 'at' HH:mm:ss vvvv"  1996.07.10 AD at 15:08:56 Pacific Time
- *     "EEE, MMM d, ''yy"                 Wed, July 10, '96
- *     "h:mm a"                           12:08 PM
- *     "hh 'o''clock' a, zzzz"            12 o'clock PM, Pacific Daylight Time
- *     "K:mm a, vvv"                      0:00 PM, PT
- *     "yyyyy.MMMMM.dd GGG hh:mm aaa"     01996.July.10 AD 12:08 PM
- *
- * When parsing a date string using the abbreviated year pattern ("yy"),
- * DateFormat must interpret the abbreviated year relative to some
- * century. It does this by adjusting dates to be within 80 years before and 20
- * years after the time the parse function is called. For example, using a
- * pattern of "MM/dd/yy" and a DateParse instance created on Jan 1, 1997,
- * the string "01/11/12" would be interpreted as Jan 11, 2012 while the string
- * "05/04/64" would be interpreted as May 4, 1964. During parsing, only
- * strings consisting of exactly two digits, as defined by {@link
- * java.lang.Character#isDigit(char)}, will be parsed into the default
- * century. Any other numeric string, such as a one digit string, a three or
- * more digit string will be interpreted as its face value.
- *
- * If the year pattern does not have exactly two 'y' characters, the year is
- * interpreted literally, regardless of the number of digits. So using the
- * pattern "MM/dd/yyyy", "01/11/12" parses to Jan 11, 12 A.D.
- */
-
-class DateFormat {
-
-  /**
-   * Creates a new DateFormat, using the format specified by [newPattern]. For
-   * forms that match one of our predefined skeletons, we look up the
-   * corresponding pattern in [locale] (or in the default locale if none is
-   * specified) and use the resulting full format string. This is the
-   * preferred usage, but if [newPattern] does not match one of the skeletons,
-   * then it is used as a format directly, but will not be adapted to suit
-   * the locale.
-   *
-   * For example, in an en_US locale, specifying the skeleton
-   *     new DateFormat.yMEd();
-   * or the explicit
-   *     new DateFormat('EEE, M/d/y');
-   * would produce the same result, a date of the form
-   *     Wed, 6/27/2012
-   * The first version would produce a different format string if used in
-   * another locale, but the second format would always be the same.
-   *
-   * If [locale] does not exist in our set of supported locales then an
-   * [ArgumentError] is thrown.
-   */
-  DateFormat([String newPattern, String locale]) {
-    // TODO(alanknight): It should be possible to specify multiple skeletons eg
-    // date, time, timezone all separately. Adding many or named parameters to
-    // the constructor seems awkward, especially with the possibility of
-    // confusion with the locale. A "fluent" interface with cascading on an
-    // instance might work better? A list of patterns is also possible.
-    _locale = Intl.verifiedLocale(locale, localeExists);
-    addPattern(newPattern);
-  }
-
-  /**
-   * Return a string representing [date] formatted according to our locale
-   * and internal format.
-   */
-  String format(DateTime date) {
-    // TODO(efortuna): read optional TimeZone argument (or similar)?
-    var result = new StringBuffer();
-    _formatFields.forEach((field) => result.write(field.format(date)));
-    return result.toString();
-  }
-
-  /**
-   * NOT YET IMPLEMENTED.
-   *
-   * Returns a date string indicating how long ago (3 hours, 2 minutes)
-   * something has happened or how long in the future something will happen
-   * given a [reference] DateTime relative to the current time.
-   */
-  String formatDuration(DateTime reference) => '';
-
-  /**
-   * NOT YET IMPLEMENTED.
-   *
-   * Formats a string indicating how long ago (negative [duration]) or how far
-   * in the future (positive [duration]) some time is with respect to a
-   * reference [date].
-   */
-  String formatDurationFrom(Duration duration, DateTime date) => '';
-
-  /**
-   * Given user input, attempt to parse the [inputString] into the anticipated
-   * format, treating it as being in the local timezone. If [inputString] does
-   * not match our format, throws a [FormatException]. This will accept dates
-   * whose values are not strictly valid, or strings with additional characters
-   * (including whitespace) after a valid date. For stricter parsing, use
-   * [parseStrict].
-   */
-  DateTime parse(String inputString, [utc = false]) =>
-      _parse(inputString, utc: utc, strict: false);
-
-  /**
-   * Given user input, attempt to parse the [inputString] "loosely" into the
-   * anticipated format, accepting some variations from the strict format.
-   *
-   * If [inputString]
-   * is accepted by [parseStrict], just return the result. If not, attempt to
-   * parse it, but accepting either upper or
-   * lower case, allowing delimiters to be missing and replaced or
-   * supplemented with whitespace,
-   * and allowing arbitrary amounts of whitespace wherever whitespace is
-   * permitted. Note that this does not allow trailing characters, the way
-   * [parse] does. It also does not allow leading whitespace on delimiters,
-   * and does not allow alternative names for months or weekdays other than
-   * those the format knows about. The restrictions are quite arbitrary and
-   * it's not known how well they'll work for locales that aren't English-like.
-   *
-   * If [inputString] does not parse, this throws a
-   * [FormatException].
-   *
-   * For example, this will accept
-   *
-   *       new DateFormat.yMMMd("en_US").parseLoose("SEp   3 2014");
-   *       new DateFormat.yMd("en_US").parseLoose("09    03/2014");
-   *
-   * It will NOT accept
-   *
-   *      // "Sept" is not a valid month name.
-   *      new DateFormat.yMMMd("en_US").parseLoose("Sept 3, 2014");
-   *      // Delimiters can't have leading whitespace.
-   *      new DateFormat.yMd("en_US").parseLoose("09 / 03 / 2014");
-   */
-  DateTime parseLoose(String inputString, [utc = false]) {
-    try {
-      return _parse(inputString, utc: utc, strict: true);
-    } on FormatException {
-      return _parseLoose(inputString.toLowerCase(), utc);
-    }
-  }
-
-  _parseLoose(String inputString, bool utc) {
-    var dateFields = new _DateBuilder();
-    if (utc) dateFields.utc = true;
-    var stream = new _Stream(inputString);
-    _formatFields.forEach((f) => f.parseLoose(stream, dateFields));
-    if (!stream.atEnd()) {
-      throw new FormatException(
-          "Characters remaining after date parsing in $inputString");
-    }
-    dateFields.verify(inputString);
-    return dateFields.asDate();
-  }
-
-  /**
-   * Given user input, attempt to parse the [inputString] into the anticipated
-   * format, treating it as being in the local timezone. If [inputString] does
-   * not match our format, throws a [FormatException]. This will reject dates
-   * whose values are not strictly valid, even if the
-   * DateTime constructor will accept them. It will also rejct strings with
-   * additional characters (including whitespace) after a valid date. For
-   * looser parsing, use [parse].
-   */
-  DateTime parseStrict(String inputString, [utc = false]) =>
-      _parse(inputString, utc: utc, strict: true);
-
-  DateTime _parse(String inputString, {utc: false, strict: false}) {
-    // TODO(alanknight): The Closure code refers to special parsing of numeric
-    // values with no delimiters, which we currently don't do. Should we?
-    var dateFields = new _DateBuilder();
-    if (utc) dateFields.utc = true;
-    var stream = new _Stream(inputString);
-    _formatFields.forEach((f) => f.parse(stream, dateFields));
-    if (strict && !stream.atEnd()) {
-      throw new FormatException(
-          "Characters remaining after date parsing in $inputString");
-    }
-    if (strict) dateFields.verify(inputString);
-    return dateFields.asDate();
-  }
-
-  /**
-   * Given user input, attempt to parse the [inputString] into the anticipated
-   * format, treating it as being in UTC.
-   *
-   * The canonical Dart style name
-   * is [parseUtc], but [parseUTC] is retained
-   * for backward-compatibility.
-   */
-  DateTime parseUTC(String inputString) => parse(inputString, true);
-
-  /**
-   * Given user input, attempt to parse the [inputString] into the anticipated
-   * format, treating it as being in UTC.
-   *
-   * The canonical Dart style name
-   * is [parseUtc], but [parseUTC] is retained
-   * for backward-compatibility.
-   */
-  DateTime parseUtc(String inputString) => parse(inputString, true);
-
-  /**
-   * Return the locale code in which we operate, e.g. 'en_US' or 'pt'.
-   */
-  String get locale => _locale;
-
-  /**
-   * Returns a list of all locales for which we have date formatting
-   * information.
-   */
-  static List<String> allLocalesWithSymbols() => dateTimeSymbols.keys.toList();
-
-  /**
-   * The named constructors for this class are all conveniences for creating
-   * instances using one of the known "skeleton" formats, and having code
-   * completion support for discovering those formats.
-   * So,
-   *     new DateFormat.yMd("en_US")
-   * is equivalent to
-   *     new DateFormat("yMd", "en_US")
-   * To create a compound format you can use these constructors in combination
-   * with the add_ methods below. e.g.
-   *     new DateFormat.yMd().add_Hms();
-   * If the optional [locale] is omitted, the format will be created using the
-   * default locale in [Intl.systemLocale].
-   */
-  DateFormat.d([locale]) : this("d", locale);
-  DateFormat.E([locale]) : this("E", locale);
-  DateFormat.EEEE([locale]) : this("EEEE", locale);
-  DateFormat.LLL([locale]) : this("LLL", locale);
-  DateFormat.LLLL([locale]) : this("LLLL", locale);
-  DateFormat.M([locale]) : this("M", locale);
-  DateFormat.Md([locale]) : this("Md", locale);
-  DateFormat.MEd([locale]) : this("MEd", locale);
-  DateFormat.MMM([locale]) : this("MMM", locale);
-  DateFormat.MMMd([locale]) : this("MMMd", locale);
-  DateFormat.MMMEd([locale]) : this("MMMEd", locale);
-  DateFormat.MMMM([locale]) : this("MMMM", locale);
-  DateFormat.MMMMd([locale]) : this("MMMMd", locale);
-  DateFormat.MMMMEEEEd([locale]) : this("MMMMEEEEd", locale);
-  DateFormat.QQQ([locale]) : this("QQQ", locale);
-  DateFormat.QQQQ([locale]) : this("QQQQ", locale);
-  DateFormat.y([locale]) : this("y", locale);
-  DateFormat.yM([locale]) : this("yM", locale);
-  DateFormat.yMd([locale]) : this("yMd", locale);
-  DateFormat.yMEd([locale]) : this("yMEd", locale);
-  DateFormat.yMMM([locale]) : this("yMMM", locale);
-  DateFormat.yMMMd([locale]) : this("yMMMd", locale);
-  DateFormat.yMMMEd([locale]) : this("yMMMEd", locale);
-  DateFormat.yMMMM([locale]) : this("yMMMM", locale);
-  DateFormat.yMMMMd([locale]) : this("yMMMMd", locale);
-  DateFormat.yMMMMEEEEd([locale]) : this("yMMMMEEEEd", locale);
-  DateFormat.yQQQ([locale]) : this("yQQQ", locale);
-  DateFormat.yQQQQ([locale]) : this("yQQQQ", locale);
-  DateFormat.H([locale]) : this("H", locale);
-  DateFormat.Hm([locale]) : this("Hm", locale);
-  DateFormat.Hms([locale]) : this("Hms", locale);
-  DateFormat.j([locale]) : this("j", locale);
-  DateFormat.jm([locale]) : this("jm", locale);
-  DateFormat.jms([locale]) : this("jms", locale);
-  DateFormat.jmv([locale]) : this("jmv", locale);
-  DateFormat.jmz([locale]) : this("jmz", locale);
-  DateFormat.jv([locale]) : this("jv", locale);
-  DateFormat.jz([locale]) : this("jz", locale);
-  DateFormat.m([locale]) : this("m", locale);
-  DateFormat.ms([locale]) : this("ms", locale);
-  DateFormat.s([locale]) : this("s", locale);
-
-  /**
-   * The "add_*" methods append a particular skeleton to the format, or set
-   * it as the only format if none was previously set. These are primarily
-   * useful for creating compound formats. For example
-   *       new DateFormat.yMd().add_Hms();
-   * would create a date format that prints both the date and the time.
-   */
-  DateFormat add_d() => addPattern("d");
-  DateFormat add_E() => addPattern("E");
-  DateFormat add_EEEE() => addPattern("EEEE");
-  DateFormat add_LLL() => addPattern("LLL");
-  DateFormat add_LLLL() => addPattern("LLLL");
-  DateFormat add_M() => addPattern("M");
-  DateFormat add_Md() => addPattern("Md");
-  DateFormat add_MEd() => addPattern("MEd");
-  DateFormat add_MMM() => addPattern("MMM");
-  DateFormat add_MMMd() => addPattern("MMMd");
-  DateFormat add_MMMEd() => addPattern("MMMEd");
-  DateFormat add_MMMM() => addPattern("MMMM");
-  DateFormat add_MMMMd() => addPattern("MMMMd");
-  DateFormat add_MMMMEEEEd() => addPattern("MMMMEEEEd");
-  DateFormat add_QQQ() => addPattern("QQQ");
-  DateFormat add_QQQQ() => addPattern("QQQQ");
-  DateFormat add_y() => addPattern("y");
-  DateFormat add_yM() => addPattern("yM");
-  DateFormat add_yMd() => addPattern("yMd");
-  DateFormat add_yMEd() => addPattern("yMEd");
-  DateFormat add_yMMM() => addPattern("yMMM");
-  DateFormat add_yMMMd() => addPattern("yMMMd");
-  DateFormat add_yMMMEd() => addPattern("yMMMEd");
-  DateFormat add_yMMMM() => addPattern("yMMMM");
-  DateFormat add_yMMMMd() => addPattern("yMMMMd");
-  DateFormat add_yMMMMEEEEd() => addPattern("yMMMMEEEEd");
-  DateFormat add_yQQQ() => addPattern("yQQQ");
-  DateFormat add_yQQQQ() => addPattern("yQQQQ");
-  DateFormat add_H() => addPattern("H");
-  DateFormat add_Hm() => addPattern("Hm");
-  DateFormat add_Hms() => addPattern("Hms");
-  DateFormat add_j() => addPattern("j");
-  DateFormat add_jm() => addPattern("jm");
-  DateFormat add_jms() => addPattern("jms");
-  DateFormat add_jmv() => addPattern("jmv");
-  DateFormat add_jmz() => addPattern("jmz");
-  DateFormat add_jv() => addPattern("jv");
-  DateFormat add_jz() => addPattern("jz");
-  DateFormat add_m() => addPattern("m");
-  DateFormat add_ms() => addPattern("ms");
-  DateFormat add_s() => addPattern("s");
-
-  /**
-   * For each of the skeleton formats we also allow the use of the corresponding
-   * ICU constant names.
-   */
-  static const String ABBR_MONTH = 'MMM';
-  static const String DAY = 'd';
-  static const String ABBR_WEEKDAY = 'E';
-  static const String WEEKDAY = 'EEEE';
-  static const String ABBR_STANDALONE_MONTH = 'LLL';
-  static const String STANDALONE_MONTH = 'LLLL';
-  static const String NUM_MONTH = 'M';
-  static const String NUM_MONTH_DAY = 'Md';
-  static const String NUM_MONTH_WEEKDAY_DAY = 'MEd';
-  static const String ABBR_MONTH_DAY = 'MMMd';
-  static const String ABBR_MONTH_WEEKDAY_DAY = 'MMMEd';
-  static const String MONTH = 'MMMM';
-  static const String MONTH_DAY = 'MMMMd';
-  static const String MONTH_WEEKDAY_DAY = 'MMMMEEEEd';
-  static const String ABBR_QUARTER = 'QQQ';
-  static const String QUARTER = 'QQQQ';
-  static const String YEAR = 'y';
-  static const String YEAR_NUM_MONTH = 'yM';
-  static const String YEAR_NUM_MONTH_DAY = 'yMd';
-  static const String YEAR_NUM_MONTH_WEEKDAY_DAY = 'yMEd';
-  static const String YEAR_ABBR_MONTH = 'yMMM';
-  static const String YEAR_ABBR_MONTH_DAY = 'yMMMd';
-  static const String YEAR_ABBR_MONTH_WEEKDAY_DAY = 'yMMMEd';
-  static const String YEAR_MONTH = 'yMMMM';
-  static const String YEAR_MONTH_DAY = 'yMMMMd';
-  static const String YEAR_MONTH_WEEKDAY_DAY = 'yMMMMEEEEd';
-  static const String YEAR_ABBR_QUARTER = 'yQQQ';
-  static const String YEAR_QUARTER = 'yQQQQ';
-  static const String HOUR24 = 'H';
-  static const String HOUR24_MINUTE = 'Hm';
-  static const String HOUR24_MINUTE_SECOND = 'Hms';
-  static const String HOUR = 'j';
-  static const String HOUR_MINUTE = 'jm';
-  static const String HOUR_MINUTE_SECOND = 'jms';
-  static const String HOUR_MINUTE_GENERIC_TZ = 'jmv';
-  static const String HOUR_MINUTE_TZ = 'jmz';
-  static const String HOUR_GENERIC_TZ = 'jv';
-  static const String HOUR_TZ = 'jz';
-  static const String MINUTE = 'm';
-  static const String MINUTE_SECOND = 'ms';
-  static const String SECOND = 's';
-
-  /** The locale in which we operate, e.g. 'en_US', or 'pt'. */
-  String _locale;
-
-  /**
-   * The full template string. This may have been specified directly, or
-   * it may have been derived from a skeleton and the locale information
-   * on how to interpret that skeleton.
-   */
-  String _pattern;
-
-  /**
-   * We parse the format string into individual [_DateFormatField] objects
-   * that are used to do the actual formatting and parsing. Do not use
-   * this variable directly, use the getter [_formatFields].
-   */
-  List<_DateFormatField> _formatFieldsPrivate;
-
-  /**
-   * Getter for [_formatFieldsPrivate] that lazily initializes it.
-   */
-  get _formatFields {
-    if (_formatFieldsPrivate == null) {
-      if (_pattern == null) _useDefaultPattern();
-      _formatFieldsPrivate = parsePattern(_pattern);
-    }
-    return _formatFieldsPrivate;
-  }
-
-  /**
-   * We are being asked to do formatting without having set any pattern.
-   * Use a default.
-   */
-  _useDefaultPattern() {
-    add_yMMMMd();
-    add_jms();
-  }
-
-  /**
-   * A series of regular expressions used to parse a format string into its
-   * component fields.
-   */
-  static List<RegExp> _matchers = [
-    // Quoted String - anything between single quotes, with escaping
-    //   of single quotes by doubling them.
-    // e.g. in the pattern "hh 'o''clock'" will match 'o''clock'
-    new RegExp("^\'(?:[^\']|\'\')*\'"),
-    // Fields - any sequence of 1 or more of the same field characters.
-    // e.g. in "hh:mm:ss" will match hh, mm, and ss. But in "hms" would
-    // match each letter individually.
-    new RegExp(
-        "^(?:G+|y+|M+|k+|S+|E+|a+|h+|K+|H+|c+|L+|Q+|d+|D+|m+|s+|v+|z+|Z+)"),
-    // Everything else - A sequence that is not quotes or field characters.
-    // e.g. in "hh:mm:ss" will match the colons.
-    new RegExp("^[^\'GyMkSEahKHcLQdDmsvzZ]+")
-  ];
-
-  /**
-   * Set our pattern, appending it to any existing patterns. Also adds a single
-   * space to separate the two.
-   */
-  _appendPattern(String inputPattern, [String separator = ' ']) {
-    _pattern =
-        _pattern == null ? inputPattern : "$_pattern$separator$inputPattern";
-  }
-
-  /**
-   * Add [inputPattern] to this instance as a pattern. If there was a previous
-   * pattern, then this appends to it, separating the two by [separator].
-   * [inputPattern] is first looked up in our list of known skeletons.
-   * If it's found there, then use the corresponding pattern for this locale.
-   * If it's not, then treat [inputPattern] as an explicit pattern.
-   */
-  DateFormat addPattern(String inputPattern, [String separator = ' ']) {
-    // TODO(alanknight): This is an expensive operation. Caching recently used
-    // formats, or possibly introducing an entire "locale" object that would
-    // cache patterns for that locale could be a good optimization.
-    // If we have already parsed the format fields, reset them.
-    _formatFieldsPrivate = null;
-    if (inputPattern == null) return this;
-    if (!_availableSkeletons.containsKey(inputPattern)) {
-      _appendPattern(inputPattern, separator);
-    } else {
-      _appendPattern(_availableSkeletons[inputPattern], separator);
-    }
-    return this;
-  }
-
-  /** Return the pattern that we use to format dates.*/
-  get pattern => _pattern;
-
-  /** Return the skeletons for our current locale. */
-  Map get _availableSkeletons => dateTimePatterns[locale];
-
-  /**
-   * Return the [DateSymbol] information for the locale. This can be useful
-   * to find lists like the names of weekdays or months in a locale, but
-   * the structure of this data may change, and it's generally better to go
-   * through the [format] and [parse] APIs. If the locale isn't present, or
-   * is uninitialized, returns null;
-   */
-  DateSymbols get dateSymbols => dateTimeSymbols[_locale];
-
-  /**
-   * Set the locale. If the locale can't be found, we also look up
-   * based on alternative versions, e.g. if we have no 'en_CA' we will
-   * look for 'en' as a fallback. It will also translate en-ca into en_CA.
-   * Null is also considered a valid value for [newLocale], indicating
-   * to use the default.
-   */
-  _setLocale(String newLocale) {
-    _locale = Intl.verifiedLocale(newLocale, localeExists);
-  }
-
-  /**
-   * Return true if the locale exists, or if it is null. The null case
-   * is interpreted to mean that we use the default locale.
-   */
-  static bool localeExists(localeName) {
-    if (localeName == null) return false;
-    return dateTimeSymbols.containsKey(localeName);
-  }
-
-  static List get _fieldConstructors => [
-    (pattern, parent) => new _DateFormatQuotedField(pattern, parent),
-    (pattern, parent) => new _DateFormatPatternField(pattern, parent),
-    (pattern, parent) => new _DateFormatLiteralField(pattern, parent)
-  ];
-
-  /** Parse the template pattern and return a list of field objects.*/
-  List parsePattern(String pattern) {
-    if (pattern == null) return null;
-    return _parsePatternHelper(pattern).reversed.toList();
-  }
-
-  /** Recursive helper for parsing the template pattern. */
-  List _parsePatternHelper(String pattern) {
-    if (pattern.isEmpty) return [];
-
-    var matched = _match(pattern);
-    if (matched == null) return [];
-
-    var parsed =
-        _parsePatternHelper(pattern.substring(matched.fullPattern().length));
-    parsed.add(matched);
-    return parsed;
-  }
-
-  /** Find elements in a string that are patterns for specific fields.*/
-  _DateFormatField _match(String pattern) {
-    for (var i = 0; i < _matchers.length; i++) {
-      var regex = _matchers[i];
-      var match = regex.firstMatch(pattern);
-      if (match != null) {
-        return _fieldConstructors[i](match.group(0), this);
-      }
-    }
-  }
-}