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# std.datetime.date

Category | Functions
--- | ---
Main date types | Date DateTime
Other date types | Month DayOfWeek TimeOfDay
Date checking | valid validTimeUnits yearIsLeapYear isTimePoint enforceValid
Date conversion | daysToDayOfWeek monthsToMonth
Time units | cmpTimeUnits timeStrings
Other | AllowDayOverflow DateTimeException

License:
Boost License 1.0.
Authors:
Jonathan M Davis

Source std/datetime/date.d

alias `DateTimeException` = core.time.TimeException;
  Exception type used by std.datetime. It's an alias to core.time.TimeException. Either can be caught without concern about which module it came from.
enum `Month`: ubyte;
  Represents the 12 months of the Gregorian year (January is 1).
  Examples:

      writeln(Date(2018, 10, 1).month); // Month.oct
      writeln(DateTime(1, 1, 1).month); // Month.jan

  `jan`
  `feb`
  `mar`
  `apr`
  `may`
  `jun`
  `jul`
  `aug`
  `sep`
  `oct`
  `nov`
  `dec`
enum `DayOfWeek`: ubyte;
  Represents the 7 days of the Gregorian week (Sunday is 0).
  Examples:

      writeln(Date(2018, 10, 1).dayOfWeek); // DayOfWeek.mon
      writeln(DateTime(5, 5, 5).dayOfWeek); // DayOfWeek.thu

  `sun`
  `mon`
  `tue`
  `wed`
  `thu`
  `fri`
  `sat`
alias `AllowDayOverflow` = std.typecons.Flag!"allowDayOverflow".Flag;
  In some date calculations, adding months or years can cause the date to fall on a day of the month which is not valid (e.g. February 29th 2001 or June 31st 2000). If overflow is allowed (as is the default), then the month will be incremented accordingly (so, February 29th 2001 would become March 1st 2001, and June 31st 2000 would become July 1st 2000). If overflow is not allowed, then the day will be adjusted to the last valid day in that month (so, February 29th 2001 would become February 28th 2001 and June 31st 2000 would become June 30th 2000).
  AllowDayOverflow only applies to calculations involving months or years.
  If set to `AllowDayOverflow`.no, then day overflow is not allowed.
  Otherwise, if set to `AllowDayOverflow`.yes, then day overflow is allowed.
immutable string[] `timeStrings`;
  Array of the strings representing time units, starting with the smallest unit and going to the largest. It does not include "nsecs".
  Includes "hnsecs" (hecto-nanoseconds (100 ns)), "usecs" (microseconds), "msecs" (milliseconds), "seconds", "minutes", "hours", "days", "weeks", "months", and "years"
struct `DateTime`;
  Combines the std.datetime.date.Date and std.datetime.date.TimeOfDay structs to give an object which holds both the date and the time. It is optimized for calendar-based operations and has no concept of time zone. For an object which is optimized for time operations based on the system time, use std.datetime.systime.SysTime. std.datetime.systime.SysTime has a concept of time zone and has much higher precision (hnsecs). `DateTime` is intended primarily for calendar-based uses rather than precise time operations.
  Examples:

      import core.time : days, seconds;

      auto dt = DateTime(2000, 6, 1, 10, 30, 0);

      writeln(dt.date); // Date(2000, 6, 1)
      writeln(dt.timeOfDay); // TimeOfDay(10, 30, 0)
      writeln(dt.dayOfYear); // 153
      writeln(dt.dayOfWeek); // DayOfWeek.thu

      dt += 10.days + 100.seconds;
      writeln(dt); // DateTime(2000, 6, 11, 10, 31, 40)

      writeln(dt.toISOExtString()); // "2000-06-11T10:31:40"
      writeln(dt.toISOString()); // "20000611T103140"
      writeln(dt.toSimpleString()); // "2000-Jun-11 10:31:40"

      writeln(DateTime.fromISOExtString("2018-01-01T12:00:00")); // DateTime(2018, 1, 1, 12, 0, 0)
      writeln(DateTime.fromISOString("20180101T120000")); // DateTime(2018, 1, 1, 12, 0, 0)
      writeln(DateTime.fromSimpleString("2018-Jan-01 12:00:00")); // DateTime(2018, 1, 1, 12, 0, 0)

  pure nothrow @nogc @safe this(in Date `date`, in TimeOfDay `tod` = TimeOfDay.init);
    Parameters:

    Date `date` | The date portion of DateTime.
    TimeOfDay `tod` | The time portion of DateTime.

  pure @safe this(int `year`, int `month`, int `day`, int `hour` = 0, int `minute` = 0, int `second` = 0);
    Parameters:

    int `year` | The year portion of the date.
    int `month` | The month portion of the date (January is 1).
    int `day` | The day portion of the date.
    int `hour` | The hour portion of the time;
    int `minute` | The minute portion of the time;
    int `second` | The second portion of the time;

  const pure nothrow @nogc @safe int `opCmp`(in DateTime `rhs`);
    Compares this DateTime with the given DateTime..
    Returns:

    this < rhs | < 0
    this == rhs | 0
    this > rhs | > 0

  const pure nothrow @nogc @property @safe Date `date`();
    The date portion of DateTime.
  pure nothrow @nogc @property @safe void `date`(in Date `date`);
    The date portion of DateTime.
    Parameters:

    Date `date` | The Date to set this DateTime's date portion to.

  const pure nothrow @nogc @property @safe TimeOfDay `timeOfDay`();
    The time portion of DateTime.
  pure nothrow @nogc @property @safe void `timeOfDay`(in TimeOfDay `tod`);
    The time portion of DateTime.
    Parameters:

    TimeOfDay `tod` | The std.datetime.date.TimeOfDay to set this DateTime's time portion to.

  const pure nothrow @nogc @property @safe short `year`();
    Year of the Gregorian Calendar. Positive numbers are A.D. Non-positive are B.C.
  pure @property @safe void `year`(int `year`);
    Year of the Gregorian Calendar. Positive numbers are A.D. Non-positive are B.C.
    Parameters:

    int `year` | The year to set this DateTime's year to.

    Throws:
    std.datetime.date.DateTimeException if the new year is not a leap year and if the resulting date would be on February 29th.
    Examples:

        writeln(DateTime(Date(1999, 7, 6), TimeOfDay(9, 7, 5)).year); // 1999
        writeln(DateTime(Date(2010, 10, 4), TimeOfDay(0, 0, 30)).year); // 2010
        writeln(DateTime(Date(-7, 4, 5), TimeOfDay(7, 45, 2)).year); // -7

  const pure @property @safe short `yearBC`();
    Year B.C. of the Gregorian Calendar counting year 0 as 1 B.C.
    Throws:
    std.datetime.date.DateTimeException if isAD is true.
    Examples:

        writeln(DateTime(Date(0, 1, 1), TimeOfDay(12, 30, 33)).yearBC); // 1
        writeln(DateTime(Date(-1, 1, 1), TimeOfDay(10, 7, 2)).yearBC); // 2
        writeln(DateTime(Date(-100, 1, 1), TimeOfDay(4, 59, 0)).yearBC); // 101

  pure @property @safe void `yearBC`(int `year`);
    Year B.C. of the Gregorian Calendar counting year 0 as 1 B.C.
    Parameters:

    int `year` | The year B.C. to set this DateTime's year to.

    Throws:
    std.datetime.date.DateTimeException if a non-positive value is given.
    Examples:

        auto dt = DateTime(Date(2010, 1, 1), TimeOfDay(7, 30, 0));
        dt.yearBC = 1;
        writeln(dt); // DateTime(Date(0, 1, 1), TimeOfDay(7, 30, 0))

        dt.yearBC = 10;
        writeln(dt); // DateTime(Date(-9, 1, 1), TimeOfDay(7, 30, 0))

  const pure nothrow @nogc @property @safe Month `month`();
    Month of a Gregorian Year.
    Examples:

        writeln(DateTime(Date(1999, 7, 6), TimeOfDay(9, 7, 5)).month); // 7
        writeln(DateTime(Date(2010, 10, 4), TimeOfDay(0, 0, 30)).month); // 10
        writeln(DateTime(Date(-7, 4, 5), TimeOfDay(7, 45, 2)).month); // 4

  pure @property @safe void `month`(Month `month`);
    Month of a Gregorian Year.
    Parameters:

    Month `month` | The month to set this DateTime's month to.

    Throws:
    std.datetime.date.DateTimeException if the given month is not a valid month.
  const pure nothrow @nogc @property @safe ubyte `day`();
    Day of a Gregorian Month.
    Examples:

        writeln(DateTime(Date(1999, 7, 6), TimeOfDay(9, 7, 5)).day); // 6
        writeln(DateTime(Date(2010, 10, 4), TimeOfDay(0, 0, 30)).day); // 4
        writeln(DateTime(Date(-7, 4, 5), TimeOfDay(7, 45, 2)).day); // 5

  pure @property @safe void `day`(int `day`);
    Day of a Gregorian Month.
    Parameters:

    int `day` | The day of the month to set this DateTime's day to.

    Throws:
    std.datetime.date.DateTimeException if the given day is not a valid day of the current month.
  const pure nothrow @nogc @property @safe ubyte `hour`();
    Hours past midnight.
  pure @property @safe void `hour`(int `hour`);
    Hours past midnight.
    Parameters:

    int `hour` | The hour of the day to set this DateTime's hour to.

    Throws:
    std.datetime.date.DateTimeException if the given hour would result in an invalid DateTime.
  const pure nothrow @nogc @property @safe ubyte `minute`();
    Minutes past the hour.
  pure @property @safe void `minute`(int `minute`);
    Minutes past the hour.
    Parameters:

    int `minute` | The minute to set this DateTime's minute to.

    Throws:
    std.datetime.date.DateTimeException if the given minute would result in an invalid DateTime.
  const pure nothrow @nogc @property @safe ubyte `second`();
    Seconds past the minute.
  pure @property @safe void `second`(int `second`);
    Seconds past the minute.
    Parameters:

    int `second` | The second to set this DateTime's second to.

    Throws:
    std.datetime.date.DateTimeException if the given seconds would result in an invalid DateTime.
  pure nothrow @nogc ref @safe DateTime `add`(string units)(long `value`, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (units == "years" || units == "months");
    Adds the given number of years or months to this DateTime. A negative number will subtract.
    Note that if day overflow is allowed, and the date with the adjusted year/month overflows the number of days in the new month, then the month will be incremented by one, and the day set to the number of days overflowed. (e.g. if the day were 31 and the new month were June, then the month would be incremented to July, and the new day would be 1). If day overflow is not allowed, then the day will be set to the last valid day in the month (e.g. June 31st would become June 30th).
    Parameters:

    units | The type of units to add ("years" or "months").
    long `value` | The number of months or years to add to this DateTime.
    AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow, causing the month to increment.

    Examples:

        auto dt1 = DateTime(2010, 1, 1, 12, 30, 33);
        dt1.add!"months"(11);
        writeln(dt1); // DateTime(2010, 12, 1, 12, 30, 33)

        auto dt2 = DateTime(2010, 1, 1, 12, 30, 33);
        dt2.add!"months"(-11);
        writeln(dt2); // DateTime(2009, 2, 1, 12, 30, 33)

        auto dt3 = DateTime(2000, 2, 29, 12, 30, 33);
        dt3.add!"years"(1);
        writeln(dt3); // DateTime(2001, 3, 1, 12, 30, 33)

        auto dt4 = DateTime(2000, 2, 29, 12, 30, 33);
        dt4.add!"years"(1, AllowDayOverflow.no);
        writeln(dt4); // DateTime(2001, 2, 28, 12, 30, 33)

  pure nothrow @nogc ref @safe DateTime `roll`(string units)(long `value`, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (units == "years" || units == "months");
    Adds the given number of years or months to this DateTime. A negative number will subtract.
    The difference between rolling and adding is that rolling does not affect larger units. Rolling a DateTime 12 months gets the exact same DateTime. However, the days can still be affected due to the differing number of days in each month.
    Because there are no units larger than years, there is no difference between adding and rolling years.
    Parameters:

    units | The type of units to add ("years" or "months").
    long `value` | The number of months or years to add to this DateTime.
    AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow, causing the month to increment.

    Examples:

        auto dt1 = DateTime(2010, 1, 1, 12, 33, 33);
        dt1.roll!"months"(1);
        writeln(dt1); // DateTime(2010, 2, 1, 12, 33, 33)

        auto dt2 = DateTime(2010, 1, 1, 12, 33, 33);
        dt2.roll!"months"(-1);
        writeln(dt2); // DateTime(2010, 12, 1, 12, 33, 33)

        auto dt3 = DateTime(1999, 1, 29, 12, 33, 33);
        dt3.roll!"months"(1);
        writeln(dt3); // DateTime(1999, 3, 1, 12, 33, 33)

        auto dt4 = DateTime(1999, 1, 29, 12, 33, 33);
        dt4.roll!"months"(1, AllowDayOverflow.no);
        writeln(dt4); // DateTime(1999, 2, 28, 12, 33, 33)

        auto dt5 = DateTime(2000, 2, 29, 12, 30, 33);
        dt5.roll!"years"(1);
        writeln(dt5); // DateTime(2001, 3, 1, 12, 30, 33)

        auto dt6 = DateTime(2000, 2, 29, 12, 30, 33);
        dt6.roll!"years"(1, AllowDayOverflow.no);
        writeln(dt6); // DateTime(2001, 2, 28, 12, 30, 33)

  pure nothrow @nogc ref @safe DateTime `roll`(string units)(long `value`)
  if (units == "days");
  pure nothrow @nogc ref @safe DateTime `roll`(string units)(long `value`)
  if (units == "hours" || units == "minutes" || units == "seconds");
    Adds the given number of units to this DateTime. A negative number will subtract.
    The difference between rolling and adding is that rolling does not affect larger units. For instance, rolling a DateTime one year's worth of days gets the exact same DateTime.
    Accepted units are "days", "minutes", "hours", "minutes", and "seconds".
    Parameters:

    units | The units to add.
    long `value` | The number of units to add to this DateTime.

    Examples:

        auto dt1 = DateTime(2010, 1, 1, 11, 23, 12);
        dt1.roll!"days"(1);
        writeln(dt1); // DateTime(2010, 1, 2, 11, 23, 12)
        dt1.roll!"days"(365);
        writeln(dt1); // DateTime(2010, 1, 26, 11, 23, 12)
        dt1.roll!"days"(-32);
        writeln(dt1); // DateTime(2010, 1, 25, 11, 23, 12)

        auto dt2 = DateTime(2010, 7, 4, 12, 0, 0);
        dt2.roll!"hours"(1);
        writeln(dt2); // DateTime(2010, 7, 4, 13, 0, 0)

        auto dt3 = DateTime(2010, 1, 1, 0, 0, 0);
        dt3.roll!"seconds"(-1);
        writeln(dt3); // DateTime(2010, 1, 1, 0, 0, 59)

  const pure nothrow @nogc @safe DateTime `opBinary`(string op)(Duration `duration`)
  if (op == "+" || op == "-");
    Gives the result of adding or subtracting a core.time.Duration from this DateTime.
    The legal types of arithmetic for DateTime using this operator are

    DateTime | + | Duration | --> | DateTime
    DateTime | - | Duration | --> | DateTime

    Parameters:

    Duration `duration` | The core.time.Duration to add to or subtract from this DateTime.

    Examples:

        import core.time : hours, seconds;

        assert(DateTime(2015, 12, 31, 23, 59, 59) + seconds(1) ==
               DateTime(2016, 1, 1, 0, 0, 0));

        assert(DateTime(2015, 12, 31, 23, 59, 59) + hours(1) ==
               DateTime(2016, 1, 1, 0, 59, 59));

        assert(DateTime(2016, 1, 1, 0, 0, 0) - seconds(1) ==
               DateTime(2015, 12, 31, 23, 59, 59));

        assert(DateTime(2016, 1, 1, 0, 59, 59) - hours(1) ==
               DateTime(2015, 12, 31, 23, 59, 59));

  pure nothrow @nogc ref @safe DateTime `opOpAssign`(string op)(Duration `duration`)
  if (op == "+" || op == "-");
    Gives the result of adding or subtracting a duration from this DateTime, as well as assigning the result to this DateTime.
    The legal types of arithmetic for DateTime using this operator are

    DateTime | + | duration | --> | DateTime
    DateTime | - | duration | --> | DateTime

    Parameters:

    Duration `duration` | The duration to add to or subtract from this DateTime.

  const pure nothrow @nogc @safe Duration `opBinary`(string op)(in DateTime `rhs`)
  if (op == "-");
    Gives the difference between two DateTimes.
    The legal types of arithmetic for DateTime using this operator are

    DateTime | - | DateTime | --> | duration

  const pure nothrow @nogc @safe int `diffMonths`(in DateTime `rhs`);
    Returns the difference between the two DateTimes in months.
    To get the difference in years, subtract the year property of two DateTimes. To get the difference in days or weeks, subtract the DateTimes themselves and use the core.time.Duration that results. Because converting between months and smaller units requires a specific date (which core.time.Durations don't have), getting the difference in months requires some math using both the year and month properties, so this is a convenience function for getting the difference in months.
    Note that the number of days in the months or how far into the month either date is is irrelevant. It is the difference in the month property combined with the difference in years * 12. So, for instance, December 31st and January 1st are one month apart just as December 1st and January 31st are one month apart.
    Parameters:

    DateTime `rhs` | The DateTime to subtract from this one.

    Examples:

        assert(DateTime(1999, 2, 1, 12, 2, 3).diffMonths(
                   DateTime(1999, 1, 31, 23, 59, 59)) == 1);

        assert(DateTime(1999, 1, 31, 0, 0, 0).diffMonths(
                   DateTime(1999, 2, 1, 12, 3, 42)) == -1);

        assert(DateTime(1999, 3, 1, 5, 30, 0).diffMonths(
                   DateTime(1999, 1, 1, 2, 4, 7)) == 2);

        assert(DateTime(1999, 1, 1, 7, 2, 4).diffMonths(
                   DateTime(1999, 3, 31, 0, 30, 58)) == -2);

  const pure nothrow @nogc @property @safe bool `isLeapYear`();
    Whether this DateTime is in a leap year.
  const pure nothrow @nogc @property @safe DayOfWeek `dayOfWeek`();
    Day of the week this DateTime is on.
  const pure nothrow @nogc @property @safe ushort `dayOfYear`();
    Day of the year this DateTime is on.
    Examples:

        writeln(DateTime(Date(1999, 1, 1), TimeOfDay(12, 22, 7)).dayOfYear); // 1
        writeln(DateTime(Date(1999, 12, 31), TimeOfDay(7, 2, 59)).dayOfYear); // 365
        writeln(DateTime(Date(2000, 12, 31), TimeOfDay(21, 20, 0)).dayOfYear); // 366

  pure @property @safe void `dayOfYear`(int `day`);
    Day of the year.
    Parameters:

    int `day` | The day of the year to set which day of the year this DateTime is on.

  const pure nothrow @nogc @property @safe int `dayOfGregorianCal`();
    The Xth day of the Gregorian Calendar that this DateTime is on.
    Examples:

        writeln(DateTime(Date(1, 1, 1), TimeOfDay(0, 0, 0)).dayOfGregorianCal); // 1
        writeln(DateTime(Date(1, 12, 31), TimeOfDay(23, 59, 59)).dayOfGregorianCal); // 365
        writeln(DateTime(Date(2, 1, 1), TimeOfDay(2, 2, 2)).dayOfGregorianCal); // 366

        writeln(DateTime(Date(0, 12, 31), TimeOfDay(7, 7, 7)).dayOfGregorianCal); // 0
        writeln(DateTime(Date(0, 1, 1), TimeOfDay(19, 30, 0)).dayOfGregorianCal); // -365
        writeln(DateTime(Date(-1, 12, 31), TimeOfDay(4, 7, 0)).dayOfGregorianCal); // -366

        writeln(DateTime(Date(2000, 1, 1), TimeOfDay(9, 30, 20)).dayOfGregorianCal); // 730_120
        writeln(DateTime(Date(2010, 12, 31), TimeOfDay(15, 45, 50)).dayOfGregorianCal); // 734_137

  pure nothrow @nogc @property @safe void `dayOfGregorianCal`(int `days`);
    The Xth day of the Gregorian Calendar that this DateTime is on. Setting this property does not affect the time portion of DateTime.
    Parameters:

    int `days` | The day of the Gregorian Calendar to set this DateTime to.

    Examples:

        auto dt = DateTime(Date.init, TimeOfDay(12, 0, 0));
        dt.dayOfGregorianCal = 1;
        writeln(dt); // DateTime(Date(1, 1, 1), TimeOfDay(12, 0, 0))

        dt.dayOfGregorianCal = 365;
        writeln(dt); // DateTime(Date(1, 12, 31), TimeOfDay(12, 0, 0))

        dt.dayOfGregorianCal = 366;
        writeln(dt); // DateTime(Date(2, 1, 1), TimeOfDay(12, 0, 0))

        dt.dayOfGregorianCal = 0;
        writeln(dt); // DateTime(Date(0, 12, 31), TimeOfDay(12, 0, 0))

        dt.dayOfGregorianCal = -365;
        writeln(dt); // DateTime(Date(-0, 1, 1), TimeOfDay(12, 0, 0))

        dt.dayOfGregorianCal = -366;
        writeln(dt); // DateTime(Date(-1, 12, 31), TimeOfDay(12, 0, 0))

        dt.dayOfGregorianCal = 730_120;
        writeln(dt); // DateTime(Date(2000, 1, 1), TimeOfDay(12, 0, 0))

        dt.dayOfGregorianCal = 734_137;
        writeln(dt); // DateTime(Date(2010, 12, 31), TimeOfDay(12, 0, 0))

  const pure nothrow @property @safe ubyte `isoWeek`();
    The ISO 8601 week of the year that this DateTime is in.
    See Also:
    ISO Week Date
  const pure nothrow @property @safe DateTime `endOfMonth`();
    DateTime for the last day in the month that this DateTime is in. The time portion of endOfMonth is always 23:59:59.
    Examples:

        assert(DateTime(Date(1999, 1, 6), TimeOfDay(0, 0, 0)).endOfMonth ==
               DateTime(Date(1999, 1, 31), TimeOfDay(23, 59, 59)));

        assert(DateTime(Date(1999, 2, 7), TimeOfDay(19, 30, 0)).endOfMonth ==
               DateTime(Date(1999, 2, 28), TimeOfDay(23, 59, 59)));

        assert(DateTime(Date(2000, 2, 7), TimeOfDay(5, 12, 27)).endOfMonth ==
               DateTime(Date(2000, 2, 29), TimeOfDay(23, 59, 59)));

        assert(DateTime(Date(2000, 6, 4), TimeOfDay(12, 22, 9)).endOfMonth ==
               DateTime(Date(2000, 6, 30), TimeOfDay(23, 59, 59)));

  const pure nothrow @nogc @property @safe ubyte `daysInMonth`();
    The last day in the month that this DateTime is in.
    Examples:

        writeln(DateTime(Date(1999, 1, 6), TimeOfDay(0, 0, 0)).daysInMonth); // 31
        writeln(DateTime(Date(1999, 2, 7), TimeOfDay(19, 30, 0)).daysInMonth); // 28
        writeln(DateTime(Date(2000, 2, 7), TimeOfDay(5, 12, 27)).daysInMonth); // 29
        writeln(DateTime(Date(2000, 6, 4), TimeOfDay(12, 22, 9)).daysInMonth); // 30

  const pure nothrow @nogc @property @safe bool `isAD`();
    Whether the current year is a date in A.D.
    Examples:

        assert(DateTime(Date(1, 1, 1), TimeOfDay(12, 7, 0)).isAD);
        assert(DateTime(Date(2010, 12, 31), TimeOfDay(0, 0, 0)).isAD);
        assert(!DateTime(Date(0, 12, 31), TimeOfDay(23, 59, 59)).isAD);
        assert(!DateTime(Date(-2010, 1, 1), TimeOfDay(2, 2, 2)).isAD);

  const pure nothrow @nogc @property @safe long `julianDay`();
    The Julian day for this DateTime at the given time. For example, prior to noon, 1996-03-31 would be the Julian day number 2_450_173, so this function returns 2_450_173, while from noon onward, the julian day number would be 2_450_174, so this function returns 2_450_174.
  const pure nothrow @nogc @property @safe long `modJulianDay`();
    The modified Julian day for any time on this date (since, the modified Julian day changes at midnight).
  const pure nothrow @safe string `toISOString`();
  const void `toISOString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this DateTime to a string with the format YYYYMMDDTHHMMSS. If `writer` is set, the resulting string will be written directly to it.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
    Examples:

        assert(DateTime(Date(2010, 7, 4), TimeOfDay(7, 6, 12)).toISOString() ==
               "20100704T070612");

        assert(DateTime(Date(1998, 12, 25), TimeOfDay(2, 15, 0)).toISOString() ==
               "19981225T021500");

        assert(DateTime(Date(0, 1, 5), TimeOfDay(23, 9, 59)).toISOString() ==
               "00000105T230959");

        assert(DateTime(Date(-4, 1, 5), TimeOfDay(0, 0, 2)).toISOString() ==
               "-00040105T000002");

  const pure nothrow @safe string `toISOExtString`();
  const void `toISOExtString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this DateTime to a string with the format YYYY-MM-DDTHH:MM:SS. If `writer` is set, the resulting string will be written directly to it.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
    Examples:

        assert(DateTime(Date(2010, 7, 4), TimeOfDay(7, 6, 12)).toISOExtString() ==
               "2010-07-04T07:06:12");

        assert(DateTime(Date(1998, 12, 25), TimeOfDay(2, 15, 0)).toISOExtString() ==
               "1998-12-25T02:15:00");

        assert(DateTime(Date(0, 1, 5), TimeOfDay(23, 9, 59)).toISOExtString() ==
               "0000-01-05T23:09:59");

        assert(DateTime(Date(-4, 1, 5), TimeOfDay(0, 0, 2)).toISOExtString() ==
               "-0004-01-05T00:00:02");

  const pure nothrow @safe string `toSimpleString`();
  const void `toSimpleString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this DateTime to a string with the format YYYY-Mon-DD HH:MM:SS. If `writer` is set, the resulting string will be written directly to it.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
    Examples:

        assert(DateTime(Date(2010, 7, 4), TimeOfDay(7, 6, 12)).toSimpleString() ==
               "2010-Jul-04 07:06:12");

        assert(DateTime(Date(1998, 12, 25), TimeOfDay(2, 15, 0)).toSimpleString() ==
               "1998-Dec-25 02:15:00");

        assert(DateTime(Date(0, 1, 5), TimeOfDay(23, 9, 59)).toSimpleString() ==
               "0000-Jan-05 23:09:59");

        assert(DateTime(Date(-4, 1, 5), TimeOfDay(0, 0, 2)).toSimpleString() ==
               "-0004-Jan-05 00:00:02");

  const pure nothrow @safe string `toString`();
  const void `toString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this DateTime to a string.
    This function exists to make it easy to convert a DateTime to a string for code that does not care what the exact format is - just that it presents the information in a clear manner. It also makes it easy to simply convert a DateTime to a string when using functions such as to!string, format, or writeln which use toString to convert user-defined types. So, it is unlikely that much code will call toString directly.
    The format of the string is purposefully unspecified, and code that cares about the format of the string should use toISOString, toISOExtString, toSimpleString, or some other custom formatting function that explicitly generates the format that the code needs. The reason is that the code is then clear about what format it's using, making it less error-prone to maintain the code and interact with other software that consumes the generated strings. It's for this same reason that DateTime has no fromString function, whereas it does have fromISOString, fromISOExtString, and fromSimpleString.
    The format returned by toString may or may not change in the future.
  pure @safe DateTime `fromISOString`(S)(in S `isoString`)
  if (isSomeString!S);
    Creates a DateTime from a string with the format YYYYMMDDTHHMMSS. Whitespace is stripped from the given string.
    Parameters:

    S `isoString` | A string formatted in the ISO format for dates and times.

    Throws:
    std.datetime.date.DateTimeException if the given string is not in the ISO format or if the resulting DateTime would not be valid.
  pure @safe DateTime `fromISOExtString`(S)(in S `isoExtString`)
  if (isSomeString!S);
    Creates a DateTime from a string with the format YYYY-MM-DDTHH:MM:SS. Whitespace is stripped from the given string.
    Parameters:

    S `isoExtString` | A string formatted in the ISO Extended format for dates and times.

    Throws:
    std.datetime.date.DateTimeException if the given string is not in the ISO Extended format or if the resulting DateTime would not be valid.
  pure @safe DateTime `fromSimpleString`(S)(in S `simpleString`)
  if (isSomeString!S);
    Creates a DateTime from a string with the format YYYY-Mon-DD HH:MM:SS. Whitespace is stripped from the given string.
    Parameters:

    S `simpleString` | A string formatted in the way that toSimpleString formats dates and times.

    Throws:
    std.datetime.date.DateTimeException if the given string is not in the correct format or if the resulting DateTime would not be valid.
  static pure nothrow @nogc @property @safe DateTime `min`();
    Returns the DateTime farthest in the past which is representable by DateTime.
  static pure nothrow @nogc @property @safe DateTime `max`();
    Returns the DateTime farthest in the future which is representable by DateTime.
struct `Date`;
  Represents a date in the Proleptic Gregorian Calendar ranging from 32,768 B.C. to 32,767 A.D. Positive years are A.D. Non-positive years are B.C.
  Year, month, and day are kept separately internally so that `Date` is optimized for calendar-based operations.
  `Date` uses the Proleptic Gregorian Calendar, so it assumes the Gregorian leap year calculations for its entire length. As per ISO 8601, it treats 1 B.C. as year 0, i.e. 1 B.C. is 0, 2 B.C. is -1, etc. Use yearBC to use B.C. as a positive integer with 1 B.C. being the year prior to 1 A.D.
  Year 0 is a leap year.
  Examples:

      import core.time : days;

      auto d = Date(2000, 6, 1);

      writeln(d.dayOfYear); // 153
      writeln(d.dayOfWeek); // DayOfWeek.thu

      d += 10.days;
      writeln(d); // Date(2000, 6, 11)

      writeln(d.toISOExtString()); // "2000-06-11"
      writeln(d.toISOString()); // "20000611"
      writeln(d.toSimpleString()); // "2000-Jun-11"

      writeln(Date.fromISOExtString("2018-01-01")); // Date(2018, 1, 1)
      writeln(Date.fromISOString("20180101")); // Date(2018, 1, 1)
      writeln(Date.fromSimpleString("2018-Jan-01")); // Date(2018, 1, 1)

  pure @safe this(int `year`, int `month`, int `day`);
    Throws:
    std.datetime.date.DateTimeException if the resulting Date would not be valid.
    Parameters:

    int `year` | Year of the Gregorian Calendar. Positive values are A.D. Non-positive values are B.C. with year 0 being the year prior to 1 A.D.
    int `month` | Month of the year (January is 1).
    int `day` | Day of the month.

  pure nothrow @nogc @safe this(int `day`);
    Parameters:

    int `day` | The Xth day of the Gregorian Calendar that the constructed Date will be for.

  const pure nothrow @nogc @safe int `opCmp`(in Date `rhs`);
    Compares this Date with the given Date.
    Returns:

    this < rhs | < 0
    this == rhs | 0
    this > rhs | > 0

  const pure nothrow @nogc @property @safe short `year`();
    Year of the Gregorian Calendar. Positive numbers are A.D. Non-positive are B.C.
    Examples:

        writeln(Date(1999, 7, 6).year); // 1999
        writeln(Date(2010, 10, 4).year); // 2010
        writeln(Date(-7, 4, 5).year); // -7

  pure @property @safe void `year`(int `year`);
    Year of the Gregorian Calendar. Positive numbers are A.D. Non-positive are B.C.
    Parameters:

    int `year` | The year to set this Date's year to.

    Throws:
    std.datetime.date.DateTimeException if the new year is not a leap year and the resulting date would be on February 29th.
    Examples:

        writeln(Date(1999, 7, 6).year); // 1999
        writeln(Date(2010, 10, 4).year); // 2010
        writeln(Date(-7, 4, 5).year); // -7

  const pure @property @safe ushort `yearBC`();
    Year B.C. of the Gregorian Calendar counting year 0 as 1 B.C.
    Throws:
    std.datetime.date.DateTimeException if isAD is true.
    Examples:

        writeln(Date(0, 1, 1).yearBC); // 1
        writeln(Date(-1, 1, 1).yearBC); // 2
        writeln(Date(-100, 1, 1).yearBC); // 101

  pure @property @safe void `yearBC`(int `year`);
    Year B.C. of the Gregorian Calendar counting year 0 as 1 B.C.
    Parameters:

    int `year` | The year B.C. to set this Date's year to.

    Throws:
    std.datetime.date.DateTimeException if a non-positive value is given.
    Examples:

        auto date = Date(2010, 1, 1);
        date.yearBC = 1;
        writeln(date); // Date(0, 1, 1)

        date.yearBC = 10;
        writeln(date); // Date(-9, 1, 1)

  const pure nothrow @nogc @property @safe Month `month`();
    Month of a Gregorian Year.
    Examples:

        writeln(Date(1999, 7, 6).month); // 7
        writeln(Date(2010, 10, 4).month); // 10
        writeln(Date(-7, 4, 5).month); // 4

  pure @property @safe void `month`(Month `month`);
    Month of a Gregorian Year.
    Parameters:

    Month `month` | The month to set this Date's month to.

    Throws:
    std.datetime.date.DateTimeException if the given month is not a valid month or if the current day would not be valid in the given month.
  const pure nothrow @nogc @property @safe ubyte `day`();
    Day of a Gregorian Month.
    Examples:

        writeln(Date(1999, 7, 6).day); // 6
        writeln(Date(2010, 10, 4).day); // 4
        writeln(Date(-7, 4, 5).day); // 5

  pure @property @safe void `day`(int `day`);
    Day of a Gregorian Month.
    Parameters:

    int `day` | The day of the month to set this Date's day to.

    Throws:
    std.datetime.date.DateTimeException if the given day is not a valid day of the current month.
  pure nothrow @nogc ref @safe Date `add`(string units)(long `value`, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (units == "years");
    Adds the given number of years or months to this Date. A negative number will subtract.
    Note that if day overflow is allowed, and the date with the adjusted year/month overflows the number of days in the new month, then the month will be incremented by one, and the day set to the number of days overflowed. (e.g. if the day were 31 and the new month were June, then the month would be incremented to July, and the new day would be 1). If day overflow is not allowed, then the day will be set to the last valid day in the month (e.g. June 31st would become June 30th).
    Parameters:

    units | The type of units to add ("years" or "months").
    long `value` | The number of months or years to add to this Date.
    AllowDayOverflow `allowOverflow` | Whether the day should be allowed to overflow, causing the month to increment.

    Examples:

        auto d1 = Date(2010, 1, 1);
        d1.add!"months"(11);
        writeln(d1); // Date(2010, 12, 1)

        auto d2 = Date(2010, 1, 1);
        d2.add!"months"(-11);
        writeln(d2); // Date(2009, 2, 1)

        auto d3 = Date(2000, 2, 29);
        d3.add!"years"(1);
        writeln(d3); // Date(2001, 3, 1)

        auto d4 = Date(2000, 2, 29);
        d4.add!"years"(1, AllowDayOverflow.no);
        writeln(d4); // Date(2001, 2, 28)

  pure nothrow @nogc ref @safe Date `roll`(string units)(long `value`, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (units == "years");
    Adds the given number of years or months to this Date. A negative number will subtract.
    The difference between rolling and adding is that rolling does not affect larger units. Rolling a Date 12 months gets the exact same Date. However, the days can still be affected due to the differing number of days in each month.
    Because there are no units larger than years, there is no difference between adding and rolling years.
    Parameters:

    units | The type of units to add ("years" or "months").
    long `value` | The number of months or years to add to this Date.
    AllowDayOverflow `allowOverflow` | Whether the day should be allowed to overflow, causing the month to increment.

    Examples:

        auto d1 = Date(2010, 1, 1);
        d1.roll!"months"(1);
        writeln(d1); // Date(2010, 2, 1)

        auto d2 = Date(2010, 1, 1);
        d2.roll!"months"(-1);
        writeln(d2); // Date(2010, 12, 1)

        auto d3 = Date(1999, 1, 29);
        d3.roll!"months"(1);
        writeln(d3); // Date(1999, 3, 1)

        auto d4 = Date(1999, 1, 29);
        d4.roll!"months"(1, AllowDayOverflow.no);
        writeln(d4); // Date(1999, 2, 28)

        auto d5 = Date(2000, 2, 29);
        d5.roll!"years"(1);
        writeln(d5); // Date(2001, 3, 1)

        auto d6 = Date(2000, 2, 29);
        d6.roll!"years"(1, AllowDayOverflow.no);
        writeln(d6); // Date(2001, 2, 28)

  pure nothrow @nogc ref @safe Date `roll`(string units)(long `days`)
  if (units == "`days`");
    Adds the given number of units to this Date. A negative number will subtract.
    The difference between rolling and adding is that rolling does not affect larger units. For instance, rolling a Date one year's worth of days gets the exact same Date.
    The only accepted units are "`days`".
    Parameters:

    units | The units to add. Must be "`days`".
    long `days` | The number of days to add to this Date.

    Examples:

        auto d = Date(2010, 1, 1);
        d.roll!"days"(1);
        writeln(d); // Date(2010, 1, 2)
        d.roll!"days"(365);
        writeln(d); // Date(2010, 1, 26)
        d.roll!"days"(-32);
        writeln(d); // Date(2010, 1, 25)

  const pure nothrow @nogc @safe Date `opBinary`(string op)(Duration `duration`)
  if (op == "+" || op == "-");
    Gives the result of adding or subtracting a core.time.Duration from
    The legal types of arithmetic for Date using this operator are

    Date | + | Duration | --> | Date
    Date | - | Duration | --> | Date

    Parameters:

    Duration `duration` | The core.time.Duration to add to or subtract from this Date.

    Examples:

        import core.time : days;

        writeln(Date(2015, 12, 31) + days(1)); // Date(2016, 1, 1)
        writeln(Date(2004, 2, 26) + days(4)); // Date(2004, 3, 1)

        writeln(Date(2016, 1, 1) - days(1)); // Date(2015, 12, 31)
        writeln(Date(2004, 3, 1) - days(4)); // Date(2004, 2, 26)

  pure nothrow @nogc ref @safe Date `opOpAssign`(string op)(Duration `duration`)
  if (op == "+" || op == "-");
    Gives the result of adding or subtracting a core.time.Duration from this Date, as well as assigning the result to this Date.
    The legal types of arithmetic for Date using this operator are

    Date | + | Duration | --> | Date
    Date | - | Duration | --> | Date

    Parameters:

    Duration `duration` | The core.time.Duration to add to or subtract from this Date.

  const pure nothrow @nogc @safe Duration `opBinary`(string op)(in Date `rhs`)
  if (op == "-");
    Gives the difference between two Dates.
    The legal types of arithmetic for Date using this operator are

    Date | - | Date | --> | duration

  const pure nothrow @nogc @safe int `diffMonths`(in Date `rhs`);
    Returns the difference between the two Dates in months.
    To get the difference in years, subtract the year property of two Dates. To get the difference in days or weeks, subtract the Dates themselves and use the core.time.Duration that results. Because converting between months and smaller units requires a specific date (which core.time.Durations don't have), getting the difference in months requires some math using both the year and month properties, so this is a convenience function for getting the difference in months.
    Note that the number of days in the months or how far into the month either Date is is irrelevant. It is the difference in the month property combined with the difference in years * 12. So, for instance, December 31st and January 1st are one month apart just as December 1st and January 31st are one month apart.
    Parameters:

    Date `rhs` | The Date to subtract from this one.

    Examples:

        writeln(Date(1999, 2, 1).diffMonths(Date(1999, 1, 31))); // 1
        writeln(Date(1999, 1, 31).diffMonths(Date(1999, 2, 1))); // -1
        writeln(Date(1999, 3, 1).diffMonths(Date(1999, 1, 1))); // 2
        writeln(Date(1999, 1, 1).diffMonths(Date(1999, 3, 31))); // -2

  const pure nothrow @nogc @property @safe bool `isLeapYear`();
    Whether this Date is in a leap year.
  const pure nothrow @nogc @property @safe DayOfWeek `dayOfWeek`();
    Day of the week this Date is on.
  const pure nothrow @nogc @property @safe ushort `dayOfYear`();
    Day of the year this Date is on.
    Examples:

        writeln(Date(1999, 1, 1).dayOfYear); // 1
        writeln(Date(1999, 12, 31).dayOfYear); // 365
        writeln(Date(2000, 12, 31).dayOfYear); // 366

  pure @property @safe void `dayOfYear`(int `day`);
    Day of the year.
    Parameters:

    int `day` | The day of the year to set which day of the year this Date is on.

    Throws:
    std.datetime.date.DateTimeException if the given day is an invalid day of the year.
  const pure nothrow @nogc @property @safe int `dayOfGregorianCal`();
    The Xth day of the Gregorian Calendar that this Date is on.
    Examples:

        writeln(Date(1, 1, 1).dayOfGregorianCal); // 1
        writeln(Date(1, 12, 31).dayOfGregorianCal); // 365
        writeln(Date(2, 1, 1).dayOfGregorianCal); // 366

        writeln(Date(0, 12, 31).dayOfGregorianCal); // 0
        writeln(Date(0, 1, 1).dayOfGregorianCal); // -365
        writeln(Date(-1, 12, 31).dayOfGregorianCal); // -366

        writeln(Date(2000, 1, 1).dayOfGregorianCal); // 730_120
        writeln(Date(2010, 12, 31).dayOfGregorianCal); // 734_137

  pure nothrow @nogc @property @safe void `dayOfGregorianCal`(int `day`);
    The Xth day of the Gregorian Calendar that this Date is on.
    Parameters:

    int `day` | The day of the Gregorian Calendar to set this Date to.

    Examples:

        auto date = Date.init;
        date.dayOfGregorianCal = 1;
        writeln(date); // Date(1, 1, 1)

        date.dayOfGregorianCal = 365;
        writeln(date); // Date(1, 12, 31)

        date.dayOfGregorianCal = 366;
        writeln(date); // Date(2, 1, 1)

        date.dayOfGregorianCal = 0;
        writeln(date); // Date(0, 12, 31)

        date.dayOfGregorianCal = -365;
        writeln(date); // Date(-0, 1, 1)

        date.dayOfGregorianCal = -366;
        writeln(date); // Date(-1, 12, 31)

        date.dayOfGregorianCal = 730_120;
        writeln(date); // Date(2000, 1, 1)

        date.dayOfGregorianCal = 734_137;
        writeln(date); // Date(2010, 12, 31)

  const pure nothrow @property @safe ubyte `isoWeek`();
    The ISO 8601 week of the year that this Date is in.
    See Also:
    ISO Week Date
  const pure nothrow @property @safe Date `endOfMonth`();
    Date for the last day in the month that this Date is in.
    Examples:

        writeln(Date(1999, 1, 6).endOfMonth); // Date(1999, 1, 31)
        writeln(Date(1999, 2, 7).endOfMonth); // Date(1999, 2, 28)
        writeln(Date(2000, 2, 7).endOfMonth); // Date(2000, 2, 29)
        writeln(Date(2000, 6, 4).endOfMonth); // Date(2000, 6, 30)

  const pure nothrow @nogc @property @safe ubyte `daysInMonth`();
    The last day in the month that this Date is in.
    Examples:

        writeln(Date(1999, 1, 6).daysInMonth); // 31
        writeln(Date(1999, 2, 7).daysInMonth); // 28
        writeln(Date(2000, 2, 7).daysInMonth); // 29
        writeln(Date(2000, 6, 4).daysInMonth); // 30

  const pure nothrow @nogc @property @safe bool `isAD`();
    Whether the current year is a date in A.D.
    Examples:

        assert(Date(1, 1, 1).isAD);
        assert(Date(2010, 12, 31).isAD);
        assert(!Date(0, 12, 31).isAD);
        assert(!Date(-2010, 1, 1).isAD);

  const pure nothrow @nogc @property @safe long `julianDay`();
    The Julian day for this Date at noon (since the Julian day changes at noon).
  const pure nothrow @nogc @property @safe long `modJulianDay`();
    The modified Julian day for any time on this date (since, the modified Julian day changes at midnight).
  const pure nothrow @safe string `toISOString`();
  const void `toISOString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this Date to a string with the format YYYYMMDD. If `writer` is set, the resulting string will be written directly to it.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
    Examples:

        writeln(Date(2010, 7, 4).toISOString()); // "20100704"
        writeln(Date(1998, 12, 25).toISOString()); // "19981225"
        writeln(Date(0, 1, 5).toISOString()); // "00000105"
        writeln(Date(-4, 1, 5).toISOString()); // "-00040105"

  const pure nothrow @safe string `toISOExtString`();
  const void `toISOExtString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this Date to a string with the format YYYY-MM-DD. If `writer` is set, the resulting string will be written directly to it.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
    Examples:

        writeln(Date(2010, 7, 4).toISOExtString()); // "2010-07-04"
        writeln(Date(1998, 12, 25).toISOExtString()); // "1998-12-25"
        writeln(Date(0, 1, 5).toISOExtString()); // "0000-01-05"
        writeln(Date(-4, 1, 5).toISOExtString()); // "-0004-01-05"

  const pure nothrow @safe string `toSimpleString`();
  const void `toSimpleString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this Date to a string with the format YYYY-Mon-DD. If `writer` is set, the resulting string will be written directly to it.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
    Examples:

        writeln(Date(2010, 7, 4).toSimpleString()); // "2010-Jul-04"
        writeln(Date(1998, 12, 25).toSimpleString()); // "1998-Dec-25"
        writeln(Date(0, 1, 5).toSimpleString()); // "0000-Jan-05"
        writeln(Date(-4, 1, 5).toSimpleString()); // "-0004-Jan-05"

  const pure nothrow @safe string `toString`();
  const void `toString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this Date to a string.
    This function exists to make it easy to convert a Date to a string for code that does not care what the exact format is - just that it presents the information in a clear manner. It also makes it easy to simply convert a Date to a string when using functions such as to!string, format, or writeln which use toString to convert user-defined types. So, it is unlikely that much code will call toString directly.
    The format of the string is purposefully unspecified, and code that cares about the format of the string should use toISOString, toISOExtString, toSimpleString, or some other custom formatting function that explicitly generates the format that the code needs. The reason is that the code is then clear about what format it's using, making it less error-prone to maintain the code and interact with other software that consumes the generated strings. It's for this same reason Date has no fromString function, whereas it does have fromISOString, fromISOExtString, and fromSimpleString.
    The format returned by toString may or may not change in the future.
  pure @safe Date `fromISOString`(S)(in S `isoString`)
  if (isSomeString!S);
    Creates a Date from a string with the format YYYYMMDD. Whitespace is stripped from the given string.
    Parameters:

    S `isoString` | A string formatted in the ISO format for dates.

    Throws:
    std.datetime.date.DateTimeException if the given string is not in the ISO format or if the resulting Date would not be valid.
  pure @safe Date `fromISOExtString`(S)(in S `isoExtString`)
  if (isSomeString!S);
    Creates a Date from a string with the format YYYY-MM-DD. Whitespace is stripped from the given string.
    Parameters:

    S `isoExtString` | A string formatted in the ISO Extended format for dates.

    Throws:
    std.datetime.date.DateTimeException if the given string is not in the ISO Extended format or if the resulting Date would not be valid.
  pure @safe Date `fromSimpleString`(S)(in S `simpleString`)
  if (isSomeString!S);
    Creates a Date from a string with the format YYYY-Mon-DD. Whitespace is stripped from the given string.
    Parameters:

    S `simpleString` | A string formatted in the way that toSimpleString formats dates.

    Throws:
    std.datetime.date.DateTimeException if the given string is not in the correct format or if the resulting Date would not be valid.
  static pure nothrow @nogc @property @safe Date `min`();
    Returns the Date farthest in the past which is representable by Date.
  static pure nothrow @nogc @property @safe Date `max`();
    Returns the Date farthest in the future which is representable by Date.
struct `TimeOfDay`;
  Represents a time of day with hours, minutes, and seconds. It uses 24 hour time.
  Examples:

      import core.time : minutes, seconds;

      auto t = TimeOfDay(12, 30, 0);

      t += 10.minutes + 100.seconds;
      writeln(t); // TimeOfDay(12, 41, 40)

      writeln(t.toISOExtString()); // "12:41:40"
      writeln(t.toISOString()); // "124140"

      writeln(TimeOfDay.fromISOExtString("15:00:00")); // TimeOfDay(15, 0, 0)
      writeln(TimeOfDay.fromISOString("015000")); // TimeOfDay(1, 50, 0)

  pure @safe this(int `hour`, int `minute`, int `second` = 0);
    Parameters:

    int `hour` | Hour of the day [0 - 24).
    int `minute` | Minute of the hour [0 - 60).
    int `second` | Second of the minute [0 - 60).

    Throws:
    std.datetime.date.DateTimeException if the resulting TimeOfDay would be not be valid.
  const pure nothrow @nogc @safe int `opCmp`(in TimeOfDay `rhs`);
    Compares this TimeOfDay with the given TimeOfDay.
    Returns:

    this < rhs | < 0
    this == rhs | 0
    this > rhs | > 0

  const pure nothrow @nogc @property @safe ubyte `hour`();
    Hours past midnight.
  pure @property @safe void `hour`(int `hour`);
    Hours past midnight.
    Parameters:

    int `hour` | The hour of the day to set this TimeOfDay's hour to.

    Throws:
    std.datetime.date.DateTimeException if the given hour would result in an invalid TimeOfDay.
  const pure nothrow @nogc @property @safe ubyte `minute`();
    Minutes past the hour.
  pure @property @safe void `minute`(int `minute`);
    Minutes past the hour.
    Parameters:

    int `minute` | The minute to set this TimeOfDay's minute to.

    Throws:
    std.datetime.date.DateTimeException if the given minute would result in an invalid TimeOfDay.
  const pure nothrow @nogc @property @safe ubyte `second`();
    Seconds past the minute.
  pure @property @safe void `second`(int `second`);
    Seconds past the minute.
    Parameters:

    int `second` | The second to set this TimeOfDay's second to.

    Throws:
    std.datetime.date.DateTimeException if the given second would result in an invalid TimeOfDay.
  pure nothrow @nogc ref @safe TimeOfDay `roll`(string units)(long `value`)
  if (units == "hours");
  pure nothrow @nogc ref @safe TimeOfDay `roll`(string units)(long `value`)
  if (units == "minutes" || units == "seconds");
    Adds the given number of units to this TimeOfDay. A negative number will subtract.
    The difference between rolling and adding is that rolling does not affect larger units. For instance, rolling a TimeOfDay one hours's worth of minutes gets the exact same TimeOfDay.
    Accepted units are "hours", "minutes", and "seconds".
    Parameters:

    units | The units to add.
    long `value` | The number of units to add to this TimeOfDay.

    Examples:

        auto tod1 = TimeOfDay(7, 12, 0);
        tod1.roll!"hours"(1);
        writeln(tod1); // TimeOfDay(8, 12, 0)

        auto tod2 = TimeOfDay(7, 12, 0);
        tod2.roll!"hours"(-1);
        writeln(tod2); // TimeOfDay(6, 12, 0)

        auto tod3 = TimeOfDay(23, 59, 0);
        tod3.roll!"minutes"(1);
        writeln(tod3); // TimeOfDay(23, 0, 0)

        auto tod4 = TimeOfDay(0, 0, 0);
        tod4.roll!"minutes"(-1);
        writeln(tod4); // TimeOfDay(0, 59, 0)

        auto tod5 = TimeOfDay(23, 59, 59);
        tod5.roll!"seconds"(1);
        writeln(tod5); // TimeOfDay(23, 59, 0)

        auto tod6 = TimeOfDay(0, 0, 0);
        tod6.roll!"seconds"(-1);
        writeln(tod6); // TimeOfDay(0, 0, 59)

  const pure nothrow @nogc @safe TimeOfDay `opBinary`(string op)(Duration `duration`)
  if (op == "+" || op == "-");
    Gives the result of adding or subtracting a core.time.Duration from this TimeOfDay.
    The legal types of arithmetic for TimeOfDay using this operator are

    TimeOfDay | + | Duration | --> | TimeOfDay
    TimeOfDay | - | Duration | --> | TimeOfDay

    Parameters:

    Duration `duration` | The core.time.Duration to add to or subtract from this TimeOfDay.

    Examples:

        import core.time : hours, minutes, seconds;

        writeln(TimeOfDay(12, 12, 12) + seconds(1)); // TimeOfDay(12, 12, 13)
        writeln(TimeOfDay(12, 12, 12) + minutes(1)); // TimeOfDay(12, 13, 12)
        writeln(TimeOfDay(12, 12, 12) + hours(1)); // TimeOfDay(13, 12, 12)
        writeln(TimeOfDay(23, 59, 59) + seconds(1)); // TimeOfDay(0, 0, 0)

        writeln(TimeOfDay(12, 12, 12) - seconds(1)); // TimeOfDay(12, 12, 11)
        writeln(TimeOfDay(12, 12, 12) - minutes(1)); // TimeOfDay(12, 11, 12)
        writeln(TimeOfDay(12, 12, 12) - hours(1)); // TimeOfDay(11, 12, 12)
        writeln(TimeOfDay(0, 0, 0) - seconds(1)); // TimeOfDay(23, 59, 59)

  pure nothrow @nogc ref @safe TimeOfDay `opOpAssign`(string op)(Duration `duration`)
  if (op == "+" || op == "-");
    Gives the result of adding or subtracting a core.time.Duration from this TimeOfDay, as well as assigning the result to this TimeOfDay.
    The legal types of arithmetic for TimeOfDay using this operator are

    TimeOfDay | + | Duration | --> | TimeOfDay
    TimeOfDay | - | Duration | --> | TimeOfDay

    Parameters:

    Duration `duration` | The core.time.Duration to add to or subtract from this TimeOfDay.

  const pure nothrow @nogc @safe Duration `opBinary`(string op)(in TimeOfDay `rhs`)
  if (op == "-");
    Gives the difference between two TimeOfDays.
    The legal types of arithmetic for TimeOfDay using this operator are

    TimeOfDay | - | TimeOfDay | --> | duration

    Parameters:

    TimeOfDay `rhs` | The TimeOfDay to subtract from this one.

  const pure nothrow @safe string `toISOString`();
  const void `toISOString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this TimeOfDay to a string with the format HHMMSS. If `writer` is set, the resulting string will be written directly to it.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
    Examples:

        writeln(TimeOfDay(0, 0, 0).toISOString()); // "000000"
        writeln(TimeOfDay(12, 30, 33).toISOString()); // "123033"

  const pure nothrow @safe string `toISOExtString`();
  const void `toISOExtString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this TimeOfDay to a string with the format HH:MM:SS. If `writer` is set, the resulting string will be written directly to it.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
    Examples:

        writeln(TimeOfDay(0, 0, 0).toISOExtString()); // "00:00:00"
        writeln(TimeOfDay(12, 30, 33).toISOExtString()); // "12:30:33"

  const pure nothrow @safe string `toString`();
  const void `toString`(W)(ref W `writer`)
  if (isOutputRange!(W, char));
    Converts this TimeOfDay to a string.
    This function exists to make it easy to convert a TimeOfDay to a string for code that does not care what the exact format is - just that it presents the information in a clear manner. It also makes it easy to simply convert a TimeOfDay to a string when using functions such as to!string, format, or writeln which use toString to convert user-defined types. So, it is unlikely that much code will call toString directly.
    The format of the string is purposefully unspecified, and code that cares about the format of the string should use toISOString, toISOExtString, or some other custom formatting function that explicitly generates the format that the code needs. The reason is that the code is then clear about what format it's using, making it less error-prone to maintain the code and interact with other software that consumes the generated strings. It's for this same reason that TimeOfDay has no fromString function, whereas it does have fromISOString and fromISOExtString.
    The format returned by toString may or may not change in the future.
    Parameters:

    W `writer` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
  pure @safe TimeOfDay `fromISOString`(S)(in S `isoString`)
  if (isSomeString!S);
    Creates a TimeOfDay from a string with the format HHMMSS. Whitespace is stripped from the given string.
    Parameters:

    S `isoString` | A string formatted in the ISO format for times.

    Throws:
    std.datetime.date.DateTimeException if the given string is not in the ISO format or if the resulting TimeOfDay would not be valid.
  pure @safe TimeOfDay `fromISOExtString`(S)(in S `isoExtString`)
  if (isSomeString!S);
    Creates a TimeOfDay from a string with the format HH:MM:SS. Whitespace is stripped from the given string.
    Parameters:

    S `isoExtString` | A string formatted in the ISO Extended format for times.

    Throws:
    std.datetime.date.DateTimeException if the given string is not in the ISO Extended format or if the resulting TimeOfDay would not be valid.
  static pure nothrow @nogc @property @safe TimeOfDay `min`();
    Returns midnight.
  static pure nothrow @nogc @property @safe TimeOfDay `max`();
    Returns one second short of midnight.
pure nothrow @nogc @safe bool `valid`(string units)(int `value`)
if (units == "months" || units == "hours" || units == "minutes" || units == "seconds");
  Returns whether the given value is valid for the given unit type when in a time point. Naturally, a duration is not held to a particular range, but the values in a time point are (e.g. a month must be in the range of 1 - 12 inclusive).
  Parameters:

  units | The units of time to validate.
  int `value` | The number to validate.

  Examples:

      assert(valid!"hours"(12));
      assert(!valid!"hours"(32));
      assert(valid!"months"(12));
      assert(!valid!"months"(13));

pure nothrow @nogc @safe bool `valid`(string units)(int `year`, int `month`, int `day`)
if (units == "days");
  Returns whether the given day is valid for the given year and month.
  Parameters:

  units | The units of time to validate.
  int `year` | The year of the day to validate.
  int `month` | The month of the day to validate (January is 1).
  int `day` | The day to validate.

  Examples:

      assert(valid!"days"(2016, 2, 29));
      assert(!valid!"days"(2016, 2, 30));
      assert(valid!"days"(2017, 2, 20));
      assert(!valid!"days"(2017, 2, 29));

pure @safe void `enforceValid`(string units)(int `value`, string `file` = __FILE__, size_t `line` = __LINE__)
if (units == "months" || units == "hours" || units == "minutes" || units == "seconds");
  Parameters:

  units | The units of time to validate.
  int `value` | The number to validate.
  string `file` | The file that the DateTimeException will list if thrown.
  size_t `line` | The line number that the DateTimeException will list if thrown.

  Throws:
  DateTimeException if valid!units(`value`) is false.
  Examples:

      import std.exception : assertThrown, assertNotThrown;

      assertNotThrown(enforceValid!"months"(10));
      assertNotThrown(enforceValid!"seconds"(40));

      assertThrown!DateTimeException(enforceValid!"months"(0));
      assertThrown!DateTimeException(enforceValid!"hours"(24));
      assertThrown!DateTimeException(enforceValid!"minutes"(60));
      assertThrown!DateTimeException(enforceValid!"seconds"(60));

pure @safe void `enforceValid`(string units)(int `year`, Month `month`, int `day`, string `file` = __FILE__, size_t `line` = __LINE__)
if (units == "days");
  Because the validity of the day number depends on both on the year and month of which the day is occurring, take all three variables to validate the day.
  Parameters:

  units | The units of time to validate.
  int `year` | The year of the day to validate.
  Month `month` | The month of the day to validate.
  int `day` | The day to validate.
  string `file` | The file that the DateTimeException will list if thrown.
  size_t `line` | The line number that the DateTimeException will list if thrown.

  Throws:
  DateTimeException if valid!"days"(year, month, day) is false.
  Examples:

      import std.exception : assertThrown, assertNotThrown;

      assertNotThrown(enforceValid!"days"(2000, Month.jan, 1));
      // leap year
      assertNotThrown(enforceValid!"days"(2000, Month.feb, 29));

      assertThrown!DateTimeException(enforceValid!"days"(2001, Month.feb, 29));
      assertThrown!DateTimeException(enforceValid!"days"(2000, Month.jan, 32));
      assertThrown!DateTimeException(enforceValid!"days"(2000, Month.apr, 31));

pure nothrow @nogc @safe int `daysToDayOfWeek`(DayOfWeek `currDoW`, DayOfWeek `dow`);
  Returns the number of days from the current day of the week to the given day of the week. If they are the same, then the result is 0.
  Parameters:

  DayOfWeek `currDoW` | The current day of the week.
  DayOfWeek `dow` | The day of the week to get the number of days to.

  Examples:

      writeln(daysToDayOfWeek(DayOfWeek.mon, DayOfWeek.mon)); // 0
      writeln(daysToDayOfWeek(DayOfWeek.mon, DayOfWeek.sun)); // 6
      writeln(daysToDayOfWeek(DayOfWeek.mon, DayOfWeek.wed)); // 2

pure @safe int `monthsToMonth`(int `currMonth`, int `month`);
  Returns the number of months from the current months of the year to the given month of the year. If they are the same, then the result is 0.
  Parameters:

  int `currMonth` | The current month of the year.
  int `month` | The month of the year to get the number of months to.

  Examples:

      writeln(monthsToMonth(Month.jan, Month.jan)); // 0
      writeln(monthsToMonth(Month.jan, Month.dec)); // 11
      writeln(monthsToMonth(Month.jul, Month.oct)); // 3

pure nothrow @nogc @safe bool `yearIsLeapYear`(int `year`);
  Whether the given Gregorian Year is a leap year.
  Parameters:

  int `year` | The year to to be tested.

  Examples:

      foreach (year; [1, 2, 100, 2001, 2002, 2003, 2005, 2006, 2007, 2009, 2010])
      {
          assert(!yearIsLeapYear(year));
          assert(!yearIsLeapYear(-year));
      }

      foreach (year; [0, 4, 8, 400, 800, 1600, 1996, 2000, 2004, 2008, 2012])
      {
          assert(yearIsLeapYear(year));
          assert(yearIsLeapYear(-year));
      }

enum auto `isTimePoint`(T);
  Whether the given type defines all of the necessary functions for it to function as a time point.
  1. T must define a static property named min which is the smallest value of T as Unqual!T.
  2. T must define a static property named max which is the largest value of T as Unqual!T.
  3. T must define an opBinary for addition and subtraction that accepts core.time.Duration and returns Unqual!T.
  4. T must define an opOpAssign for addition and subtraction that accepts core.time.Duration and returns ref Unqual!T.
  5. T must define a opBinary for subtraction which accepts T and returns returns core.time.Duration.
  Examples:

      import core.time : Duration;
      import std.datetime.interval : Interval;
      import std.datetime.systime : SysTime;

      static assert(isTimePoint!Date);
      static assert(isTimePoint!DateTime);
      static assert(isTimePoint!SysTime);
      static assert(isTimePoint!TimeOfDay);

      static assert(!isTimePoint!int);
      static assert(!isTimePoint!Duration);
      static assert(!isTimePoint!(Interval!SysTime));

pure nothrow @nogc @safe bool `validTimeUnits`(string[] `units`...);
  Whether all of the given strings are valid units of time.
  "nsecs" is not considered a valid unit of time. Nothing in std.datetime can handle precision greater than hnsecs, and the few functions in core.time which deal with "nsecs" deal with it explicitly.
  Examples:

      assert(validTimeUnits("msecs", "seconds", "minutes"));
      assert(validTimeUnits("days", "weeks", "months"));
      assert(!validTimeUnits("ms", "seconds", "minutes"));

pure @safe int `cmpTimeUnits`(string `lhs`, string `rhs`);
  Compares two time unit strings. "years" are the largest units and "hnsecs" are the smallest.
  Returns:

  this < rhs | < 0
  this == rhs | 0
  this > rhs | > 0

  Throws:
  DateTimeException if either of the given strings is not a valid time unit string.
  Examples:

      import std.exception : assertThrown;

      writeln(cmpTimeUnits("hours", "hours")); // 0
      assert(cmpTimeUnits("hours", "weeks") < 0);
      assert(cmpTimeUnits("months", "seconds") > 0);

      assertThrown!DateTimeException(cmpTimeUnits("month", "second"));

template `CmpTimeUnits`(string lhs, string rhs) if (validTimeUnits(lhs, rhs))
  Compares two time unit strings at compile time. "years" are the largest units and "hnsecs" are the smallest.
  This template is used instead of cmpTimeUnits because exceptions can't be thrown at compile time and cmpTimeUnits must enforce that the strings it's given are valid time unit strings. This template uses a template constraint instead.
  Returns:

  this < rhs | < 0
  this == rhs | 0
  this > rhs | > 0

  Examples:

      static assert(CmpTimeUnits!("years", "weeks") > 0);
      static assert(CmpTimeUnits!("days", "days") == 0);
      static assert(CmpTimeUnits!("seconds", "hours") < 0);

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