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спецификации, руководства, описания, API
Spec-Zone .ru
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DateTime(3)                          User Contributed Perl Documentation                         DateTime(3)



NAME
       DateTime - A date and time object

VERSION
       version 0.70

SYNOPSIS
         use DateTime;

         $dt = DateTime->new(
             year       => 1964,
             month      => 10,
             day        => 16,
             hour       => 16,
             minute     => 12,
             second     => 47,
             nanosecond => 500000000,
             time_zone  => 'Asia/Taipei',
         );

         $dt = DateTime->from_epoch( epoch => $epoch );
         $dt = DateTime->now; # same as ( epoch => time() )

         $year   = $dt->year;
         $month  = $dt->month;          # 1-12

         $day    = $dt->day;            # 1-31

         $dow    = $dt->day_of_week;    # 1-7 (Monday is 1)

         $hour   = $dt->hour;           # 0-23
         $minute = $dt->minute;         # 0-59

         $second = $dt->second;         # 0-61 (leap seconds!)

         $doy    = $dt->day_of_year;    # 1-366 (leap years)

         $doq    = $dt->day_of_quarter; # 1..

         $qtr    = $dt->quarter;        # 1-4

         # all of the start-at-1 methods above have corresponding start-at-0
         # methods, such as $dt->day_of_month_0, $dt->month_0 and so on

         $ymd    = $dt->ymd;           # 2002-12-06
         $ymd    = $dt->ymd('/');      # 2002/12/06

         $mdy    = $dt->mdy;           # 12-06-2002
         $mdy    = $dt->mdy('/');      # 12/06/2002

         $dmy    = $dt->dmy;           # 06-12-2002
         $dmy    = $dt->dmy('/');      # 06/12/2002

         $hms    = $dt->hms;           # 14:02:29
         $hms    = $dt->hms('!');      # 14!02!29

         $is_leap  = $dt->is_leap_year;

         # these are localizable, see Locales section
         $month_name  = $dt->month_name; # January, February, ...
         $month_abbr  = $dt->month_abbr; # Jan, Feb, ...
         $day_name    = $dt->day_name;   # Monday, Tuesday, ...
         $day_abbr    = $dt->day_abbr;   # Mon, Tue, ...

         # May not work for all possible datetime, see the docs on this
         # method for more details.
         $epoch_time  = $dt->epoch;

         $dt2 = $dt + $duration_object;

         $dt3 = $dt - $duration_object;

         $duration_object = $dt - $dt2;

         $dt->set( year => 1882 );

         $dt->set_time_zone( 'America/Chicago' );

         $dt->set_formatter( $formatter );

DESCRIPTION
       DateTime is a class for the representation of date/time combinations, and is part of the Perl
       DateTime project. For details on this project please see <http://datetime.perl.org/>. The DateTime
       site has a FAQ which may help answer many "how do I do X?" questions. The FAQ is at
       <http://datetime.perl.org/wiki/datetime/page/FAQ>.

       It represents the Gregorian calendar, extended backwards in time before its creation (in 1582). This
       is sometimes known as the "proleptic Gregorian calendar". In this calendar, the first day of the
       calendar (the epoch), is the first day of year 1, which corresponds to the date which was
       (incorrectly) believed to be the birth of Jesus Christ.

       The calendar represented does have a year 0, and in that way differs from how dates are often written
       using "BCE/CE" or "BC/AD".

       For infinite datetimes, please see the DateTime::Infinite module.

USAGE
   0-based Versus 1-based Numbers
       The DateTime.pm module follows a simple consistent logic for determining whether or not a given
       number is 0-based or 1-based.

       Month, day of month, day of week, and day of year are 1-based. Any method that is 1-based also has an
       equivalent 0-based method ending in "_0". So for example, this class provides both "day_of_week()"
       and "day_of_week_0()" methods.

       The "day_of_week_0()" method still treats Monday as the first day of the week.

       All time-related numbers such as hour, minute, and second are 0-based.

       Years are neither, as they can be both positive or negative, unlike any other datetime component.
       There is a year 0.

       There is no "quarter_0()" method.

   Error Handling
       Some errors may cause this module to die with an error string. This can only happen when calling
       constructor methods, methods that change the object, such as "set()", or methods that take
       parameters.  Methods that retrieve information about the object, such as "year()" or "epoch()", will
       never die.

   Locales
       All the object methods which return names or abbreviations return data based on a locale. This is
       done by setting the locale when constructing a DateTime object. There is also a "DefaultLocale()"
       class method which may be used to set the default locale for all DateTime objects created. If this is
       not set, then "en_US" is used.

   Floating DateTimes
       The default time zone for new DateTime objects, except where stated otherwise, is the "floating" time
       zone. This concept comes from the iCal standard. A floating datetime is one which is not anchored to
       any particular time zone. In addition, floating datetimes do not include leap seconds, since we
       cannot apply them without knowing the datetime's time zone.

       The results of date math and comparison between a floating datetime and one with a real time zone are
       not really valid, because one includes leap seconds and the other does not. Similarly, the results of
       datetime math between two floating datetimes and two datetimes with time zones are not really
       comparable.

       If you are planning to use any objects with a real time zone, it is strongly recommended that you do
       not mix these with floating datetimes.

   Math
       If you are going to be using doing date math, please read the section "How Datetime Math Works".

   Time Zone Warnings
       Determining the local time zone for a system can be slow. If $ENV{TZ} is not set, it may involve
       reading a number of files in /etc or elsewhere. If you know that the local time zone won't change
       while your code is running, and you need to make many objects for the local time zone, it is strongly
       recommended that you retrieve the local time zone once and cache it:

         our $App::LocalTZ = DateTime::TimeZone->new( name => 'local' );

         ... # then everywhere else

         my $dt = DateTime->new( ..., time_zone => $App::LocalTZ );

       DateTime itself does not do this internally because local time zones can change, and there's no good
       way to determine if it's changed without doing all the work to look it up.

       Do not try to use named time zones (like "America/Chicago") with dates very far in the future
       (thousands of years). The current implementation of "DateTime::TimeZone" will use a huge amount of
       memory calculating all the DST changes from now until the future date. Use UTC or the floating time
       zone and you will be safe.

   Methods
       Constructors

       All constructors can die when invalid parameters are given.

          DateTime->new( ... )

           This class method accepts parameters for each date and time component: "year", "month", "day",
           "hour", "minute", "second", "nanosecond".  It also accepts "locale", "time_zone", and "formatter"
           parameters.

             my $dt = DateTime->new(
                 year       => 1966,
                 month      => 10,
                 day        => 25,
                 hour       => 7,
                 minute     => 15,
                 second     => 47,
                 nanosecond => 500000000,
                 time_zone  => 'America/Chicago',
             );

           DateTime validates the "month", "day", "hour", "minute", and "second", and "nanosecond"
           parameters. The valid values for these parameters are:

                  month

                   An integer from 1-12.

                  day

                   An integer from 1-31, and it must be within the valid range of days for the specified
                   month.

                  hour

                   An integer from 0-23.

                  minute

                   An integer from 0-59.

                  second

                   An integer from 0-61 (to allow for leap seconds). Values of 60 or 61 are only allowed
                   when they match actual leap seconds.

                  nanosecond

                   An integer >= 0. If this number is greater than 1 billion, it will be normalized into the
                   second value for the DateTime object.

           Invalid parameter types (like an array reference) will cause the constructor to die.

           The value for seconds may be from 0 to 61, to account for leap seconds. If you give a value
           greater than 59, DateTime does check to see that it really matches a valid leap second.

           All of the parameters are optional except for "year". The "month" and "day" parameters both
           default to 1, while the "hour", "minute", "second", and "nanosecond" parameters all default to 0.

           The "locale" parameter should be a string matching one of the valid locales, or a
           "DateTime::Locale" object. See the DateTime::Locale documentation for details.

           The time_zone parameter can be either a scalar or a "DateTime::TimeZone" object. A string will
           simply be passed to the "DateTime::TimeZone->new" method as its "name" parameter. This string may
           be an Olson DB time zone name ("America/Chicago"), an offset string ("+0630"), or the words
           "floating" or "local". See the "DateTime::TimeZone" documentation for more details.

           The default time zone is "floating".

           The "formatter" can be either a scalar or an object, but the class specified by the scalar or the
           object must implement a "format_datetime()" method.

       Parsing Dates

       This module does not parse dates! That means there is no constructor to which you can pass things
       like "March 3, 1970 12:34".

       Instead, take a look at the various "DateTime::Format::*" modules on CPAN. These parse all sorts of
       different date formats, and you're bound to find something that can handle your particular needs.

       Ambiguous Local Times

       Because of Daylight Saving Time, it is possible to specify a local time that is ambiguous. For
       example, in the US in 2003, the transition from to saving to standard time occurred on October 26, at
       02:00:00 local time. The local clock changed from 01:59:59 (saving time) to 01:00:00 (standard time).
       This means that the hour from 01:00:00 through 01:59:59 actually occurs twice, though the UTC time
       continues to move forward.

       If you specify an ambiguous time, then the latest UTC time is always used, in effect always choosing
       standard time. In this case, you can simply subtract an hour to the object in order to move to saving
       time, for example:

         # This object represent 01:30:00 standard time
         my $dt = DateTime->new(
             year      => 2003,
             month     => 10,
             day       => 26,
             hour      => 1,
             minute    => 30,
             second    => 0,
             time_zone => 'America/Chicago',
         );

         print $dt->hms;  # prints 01:30:00

         # Now the object represent 01:30:00 saving time
         $dt->subtract( hours => 1 );

         print $dt->hms;  # still prints 01:30:00

       Alternately, you could create the object with the UTC time zone, and then call the "set_time_zone()"
       method to change the time zone. This is a good way to ensure that the time is not ambiguous.

       Invalid Local Times

       Another problem introduced by Daylight Saving Time is that certain local times just do not exist. For
       example, in the US in 2003, the transition from standard to saving time occurred on April 6, at the
       change to 2:00:00 local time. The local clock changes from 01:59:59 (standard time) to 03:00:00
       (saving time). This means that there is no 02:00:00 through 02:59:59 on April 6!

       Attempting to create an invalid time currently causes a fatal error.  This may change in future
       version of this module.

          DateTime->from_epoch( epoch => $epoch, ... )

           This class method can be used to construct a new DateTime object from an epoch time instead of
           components. Just as with the "new()" method, it accepts "time_zone", "locale", and "formatter"
           parameters.

           If the epoch value is not an integer, the part after the decimal will be converted to
           nanoseconds. This is done in order to be compatible with "Time::HiRes". If the floating portion
           extends past 9 decimal places, it will be truncated to nine, so that 1.1234567891 will become 1
           second and 123,456,789 nanoseconds.

           By default, the returned object will be in the UTC time zone.

          DateTime->now( ... )

           This class method is equivalent to calling "from_epoch()" with the value returned from Perl's
           "time()" function. Just as with the "new()" method, it accepts "time_zone" and "locale"
           parameters.

           By default, the returned object will be in the UTC time zone.

          DateTime->today( ... )

           This class method is equivalent to:

             DateTime->now->truncate( to => 'day' );

          DateTime->from_object( object => $object, ... )

           This class method can be used to construct a new DateTime object from any object that implements
           the "utc_rd_values()" method. All "DateTime::Calendar" modules must implement this method in
           order to provide cross-calendar compatibility. This method accepts a "locale" and "formatter"
           parameter

           If the object passed to this method has a "time_zone()" method, that is used to set the time zone
           of the newly created "DateTime.pm" object.

           Otherwise, the returned object will be in the floating time zone.

          DateTime->last_day_of_month( ... )

           This constructor takes the same arguments as can be given to the "new()" method, except for
           "day". Additionally, both "year" and "month" are required.

          DateTime->from_day_of_year( ... )

           This constructor takes the same arguments as can be given to the "new()" method, except that it
           does not accept a "month" or "day" argument. Instead, it requires both "year" and "day_of_year".
           The day of year must be between 1 and 366, and 366 is only allowed for leap years.

          $dt->clone()

           This object method returns a new object that is replica of the object upon which the method is
           called.

       "Get" Methods

       This class has many methods for retrieving information about an object.

          $dt->year()

           Returns the year.

          $dt->ce_year()

           Returns the year according to the BCE/CE numbering system. The year before year 1 in this system
           is year -1, aka "1 BCE".

          $dt->era_name()

           Returns the long name of the current era, something like "Before Christ". See the Locales section
           for more details.

          $dt->era_abbr()

           Returns the abbreviated name of the current era, something like "BC".  See the Locales section
           for more details.

          $dt->christian_era()

           Returns a string, either "BC" or "AD", according to the year.

          $dt->secular_era()

           Returns a string, either "BCE" or "CE", according to the year.

          $dt->year_with_era()

           Returns a string containing the year immediately followed by its era abbreviation. The year is
           the absolute value of "ce_year()", so that year 1 is "1AD" and year 0 is "1BC".

          $dt->year_with_christian_era()

           Like "year_with_era()", but uses the christian_era() to get the era name.

          $dt->year_with_secular_era()

           Like "year_with_era()", but uses the secular_era() method to get the era name.

          $dt->month()

           Returns the month of the year, from 1..12.

           Also available as "$dt->mon()".

          $dt->month_name()

           Returns the name of the current month. See the Locales section for more details.

          $dt->month_abbr()

           Returns the abbreviated name of the current month. See the Locales section for more details.

          $dt->day()

           Returns the day of the month, from 1..31.

           Also available as "$dt->mday()" and "$dt->day_of_month()".

          $dt->day_of_week()

           Returns the day of the week as a number, from 1..7, with 1 being Monday and 7 being Sunday.

           Also available as "$dt->wday()" and "$dt->dow()".

          $dt->local_day_of_week()

           Returns the day of the week as a number, from 1..7. The day corresponding to 1 will vary based on
           the locale.

          $dt->day_name()

           Returns the name of the current day of the week. See the Locales section for more details.

          $dt->day_abbr()

           Returns the abbreviated name of the current day of the week. See the Locales section for more
           details.

          $dt->day_of_year()

           Returns the day of the year.

           Also available as "$dt->doy()".

          $dt->quarter()

           Returns the quarter of the year, from 1..4.

          $dt->quarter_name()

           Returns the name of the current quarter. See the Locales section for more details.

          $dt->quarter_abbr()

           Returns the abbreviated name of the current quarter. See the Locales section for more details.

          $dt->day_of_quarter()

           Returns the day of the quarter.

           Also available as "$dt->doq()".

          $dt->weekday_of_month()

           Returns a number from 1..5 indicating which week day of the month this is. For example, June 9,
           2003 is the second Monday of the month, and so this method returns 2 for that day.

          $dt->ymd( $optional_separator )

          $dt->mdy( $optional_separator )

          $dt->dmy( $optional_separator )

           Each method returns the year, month, and day, in the order indicated by the method name. Years
           are zero-padded to four digits. Months and days are 0-padded to two digits.

           By default, the values are separated by a dash (-), but this can be overridden by passing a value
           to the method.

           The "$dt->ymd()" method is also available as "$dt->date()".

          $dt->hour()

           Returns the hour of the day, from 0..23.

          $dt->hour_1()

           Returns the hour of the day, from 1..24.

          $dt->hour_12()

           Returns the hour of the day, from 1..12.

          $dt->hour_12__()

           Returns the hour of the day, from 0..11.

          $dt->am_or_pm()

           Returns the appropriate localized abbreviation, depending on the current hour.

          $dt->minute()

           Returns the minute of the hour, from 0..59.

           Also available as "$dt->min()".

          $dt->second()

           Returns the second, from 0..61. The values 60 and 61 are used for leap seconds.

           Also available as "$dt->sec()".

          $dt->fractional_second()

           Returns the second, as a real number from 0.0 until 61.999999999

           The values 60 and 61 are used for leap seconds.

          $dt->millisecond()

           Returns the fractional part of the second as milliseconds (1E-3 seconds).

           Half a second is 500 milliseconds.

          $dt->microsecond()

           Returns the fractional part of the second as microseconds (1E-6 seconds). This value will be
           rounded to an integer.

           Half a second is 500_000 microseconds. This value will be rounded to an integer.

          $dt->nanosecond()

           Returns the fractional part of the second as nanoseconds (1E-9 seconds).

           Half a second is 500_000_000 nanoseconds.

          $dt->hms( $optional_separator )

           Returns the hour, minute, and second, all zero-padded to two digits.  If no separator is
           specified, a colon (:) is used by default.

           Also available as "$dt->time()".

          $dt->datetime()

           This method is equivalent to:

             $dt->ymd('-') . 'T' . $dt->hms(':')

           Also available as "$dt->iso8601()".

          $dt->is_leap_year()

           This method returns a true or false indicating whether or not the datetime object is in a leap
           year.

          $dt->week()

            ($week_year, $week_number) = $dt->week;

           Returns information about the calendar week which contains this datetime object. The values
           returned by this method are also available separately through the week_year and week_number
           methods.

           The first week of the year is defined by ISO as the one which contains the fourth day of January,
           which is equivalent to saying that it's the first week to overlap the new year by at least four
           days.

           Typically the week year will be the same as the year that the object is in, but dates at the very
           beginning of a calendar year often end up in the last week of the prior year, and similarly, the
           final few days of the year may be placed in the first week of the next year.

          $dt->week_year()

           Returns the year of the week. See "$dt->week()" for details.

          $dt->week_number()

           Returns the week of the year, from 1..53. See "$dt->week()" for details.

          $dt->week_of_month()

           The week of the month, from 0..5. The first week of the month is the first week that contains a
           Thursday. This is based on the ICU definition of week of month, and correlates to the ISO8601
           week of year definition. A day in the week before the week with the first Thursday will be week
           0.

          $dt->jd()

          $dt->mjd()

           These return the Julian Day and Modified Julian Day, respectively.  The value returned is a
           floating point number. The fractional portion of the number represents the time portion of the
           datetime.

          $dt->time_zone()

           This returns the "DateTime::TimeZone" object for the datetime object.

          $dt->offset()

           This returns the offset from UTC, in seconds, of the datetime object according to the time zone.

          $dt->is_dst()

           Returns a boolean indicating whether or not the datetime object is currently in Daylight Saving
           Time or not.

          $dt->time_zone_long_name()

           This is a shortcut for "$dt->time_zone->name". It's provided so that one can use
           "%{time_zone_long_name}" as a strftime format specifier.

          $dt->time_zone_short_name()

           This method returns the time zone abbreviation for the current time zone, such as "PST" or "GMT".
           These names are not definitive, and should not be used in any application intended for general
           use by users around the world.

          $dt->strftime( $format, ... )

           This method implements functionality similar to the "strftime()" method in C. However, if given
           multiple format strings, then it will return multiple scalars, one for each format string.

           See the "strftime Patterns" section for a list of all possible strftime patterns.

           If you give a pattern that doesn't exist, then it is simply treated as text.

          $dt->format_cldr( $format, ... )

           This method implements formatting based on the CLDR date patterns. If given multiple format
           strings, then it will return multiple scalars, one for each format string.

           See the "CLDR Patterns" section for a list of all possible CLDR patterns.

           If you give a pattern that doesn't exist, then it is simply treated as text.

          $dt->epoch()

           Return the UTC epoch value for the datetime object. Internally, this is implemented using
           "Time::Local", which uses the Unix epoch even on machines with a different epoch (such as MacOS).
           Datetimes before the start of the epoch will be returned as a negative number.

           The return value from this method is always an integer.

           Since the epoch does not account for leap seconds, the epoch time for 1972-12-31T23:59:60 (UTC)
           is exactly the same as that for 1973-01-01T00:00:00.

           This module uses "Time::Local" to calculate the epoch, which may or may not handle epochs before
           1904 or after 2038 (depending on the size of your system's integers, and whether or not Perl was
           compiled with 64-bit int support).

          $dt->hires_epoch()

           Returns the epoch as a floating point number. The floating point portion of the value represents
           the nanosecond value of the object.  This method is provided for compatibility with the
           "Time::HiRes" module.

          $dt->is_finite()

          $dt->is_infinite()

           These methods allow you to distinguish normal datetime objects from infinite ones. Infinite
           datetime objects are documented in DateTime::Infinite.

          $dt->utc_rd_values()

           Returns the current UTC Rata Die days, seconds, and nanoseconds as a three element list. This
           exists primarily to allow other calendar modules to create objects based on the values provided
           by this object.

          $dt->local_rd_values()

           Returns the current local Rata Die days, seconds, and nanoseconds as a three element list. This
           exists for the benefit of other modules which might want to use this information for date math,
           such as "DateTime::Event::Recurrence".

          $dt->leap_seconds()

           Returns the number of leap seconds that have happened up to the datetime represented by the
           object. For floating datetimes, this always returns 0.

          $dt->utc_rd_as_seconds()

           Returns the current UTC Rata Die days and seconds purely as seconds.  This number ignores any
           fractional seconds stored in the object, as well as leap seconds.

          $dt->locale()

           Returns the current locale object.

          $dt->formatter()

           Returns current formatter object or class. See "Formatters And Stringification" for details.

       "Set" Methods

       The remaining methods provided by "DateTime.pm", except where otherwise specified, return the object
       itself, thus making method chaining possible. For example:

         my $dt = DateTime->now->set_time_zone( 'Australia/Sydney' );

         my $first = DateTime
                       ->last_day_of_month( year => 2003, month => 3 )
                       ->add( days => 1 )
                       ->subtract( seconds => 1 );

          $dt->set( .. )

           This method can be used to change the local components of a date time, or its locale. This method
           accepts any parameter allowed by the "new()" method except for "time_zone". Time zones may be set
           using the "set_time_zone()" method.

           This method performs parameters validation just as is done in the "new()" method.

          $dt->set_year()

          $dt->set_month()

          $dt->set_day()

          $dt->set_hour()

          $dt->set_minute()

          $dt->set_second()

          $dt->set_nanosecond()

          $dt->set_locale()

           These are shortcuts to calling "set()" with a single key. They all take a single parameter.

          $dt->truncate( to => ... )

           This method allows you to reset some of the local time components in the object to their "zero"
           values. The "to" parameter is used to specify which values to truncate, and it may be one of
           "year", "month", "week", "day", "hour", "minute", or "second". For example, if "month" is
           specified, then the local day becomes 1, and the hour, minute, and second all become 0.

           If "week" is given, then the datetime is set to the beginning of the week in which it occurs, and
           the time components are all set to 0.

          $dt->set_time_zone( $tz )

           This method accepts either a time zone object or a string that can be passed as the "name"
           parameter to "DateTime::TimeZone->new()".  If the new time zone's offset is different from the
           old time zone, then the local time is adjusted accordingly.

           For example:

             my $dt = DateTime->new(
                 year      => 2000,
                 month     => 5,
                 day       => 10,
                 hour      => 15,
                 minute    => 15,
                 time_zone => 'America/Los_Angeles',
             );

             print $dt->hour; # prints 15

             $dt->set_time_zone( 'America/Chicago' );

             print $dt->hour; # prints 17

           If the old time zone was a floating time zone, then no adjustments to the local time are made,
           except to account for leap seconds. If the new time zone is floating, then the UTC time is
           adjusted in order to leave the local time untouched.

           Fans of Tsai Ming-Liang's films will be happy to know that this does work:

             my $dt = DateTime->now( time_zone => 'Asia/Taipei' );

             $dt->set_time_zone( 'Europe/Paris' );

           Yes, now we can know "ni3 na4 bian1 ji2dian3?"

          $dt->set_formatter( $formatter )

           Set the formatter for the object. See "Formatters And Stringification" for details.

           You can set this to "undef" to revert to the default formatter.

       Math Methods

       Like the set methods, math related methods always return the object itself, to allow for chaining:

         $dt->add( days => 1 )->subtract( seconds => 1 );

          $dt->duration_class()

           This returns "DateTime::Duration", but exists so that a subclass of "DateTime.pm" can provide a
           different value.

          $dt->add_duration( $duration_object )

           This method adds a "DateTime::Duration" to the current datetime. See the DateTime::Duration docs
           for more details.

          $dt->add( DateTime::Duration->new parameters )

           This method is syntactic sugar around the "add_duration()" method. It simply creates a new
           "DateTime::Duration" object using the parameters given, and then calls the "add_duration()"
           method.

          $dt->subtract_duration( $duration_object )

           When given a "DateTime::Duration" object, this method simply calls "invert()" on that object and
           passes that new duration to the "add_duration" method.

          $dt->subtract( DateTime::Duration->new parameters )

           Like "add()", this is syntactic sugar for the "subtract_duration()" method.

          $dt->subtract_datetime( $datetime )

           This method returns a new "DateTime::Duration" object representing the difference between the two
           dates. The duration is relative to the object from which $datetime is subtracted. For example:

               2003-03-15 00:00:00.00000000
            -  2003-02-15 00:00:00.00000000
            -------------------------------= ------------------------------=
            = 1 month

           Note that this duration is not an absolute measure of the amount of time between the two
           datetimes, because the length of a month varies, as well as due to the presence of leap seconds.

           The returned duration may have deltas for months, days, minutes, seconds, and nanoseconds.

          $dt->delta_md( $datetime )

          $dt->delta_days( $datetime )

           Each of these methods returns a new "DateTime::Duration" object representing some portion of the
           difference between two datetimes.  The "delta_md()" method returns a duration which contains only
           the month and day portions of the duration is represented. The "delta_days()" method returns a
           duration which contains only days.

           The "delta_md" and "delta_days" methods truncate the duration so that any fractional portion of a
           day is ignored. Both of these methods operate on the date portion of a datetime only, and so
           effectively ignore the time zone.

           Unlike the subtraction methods, these methods always return a positive (or zero) duration.

          $dt->delta_ms( $datetime )

           Returns a duration which contains only minutes and seconds. Any day and month differences to
           minutes are converted to minutes and seconds. This method also always return a positive (or zero)
           duration.

          $dt->subtract_datetime_absolute( $datetime )

           This method returns a new "DateTime::Duration" object representing the difference between the two
           dates in seconds and nanoseconds. This is the only way to accurately measure the absolute amount
           of time between two datetimes, since units larger than a second do not represent a fixed number
           of seconds.

       Class Methods

          DateTime->DefaultLocale( $locale )

           This can be used to specify the default locale to be used when creating DateTime objects. If
           unset, then "en_US" is used.

          DateTime->compare( $dt1, $dt2 )

          DateTime->compare_ignore_floating( $dt1, $dt2 )

             $cmp = DateTime->compare( $dt1, $dt2 );

             $cmp = DateTime->compare_ignore_floating( $dt1, $dt2 );

           Compare two DateTime objects. The semantics are compatible with Perl's "sort()" function; it
           returns -1 if $dt1 < $dt2, 0 if $dt1 == $dt2, 1 if $dt1 > $dt2.

           If one of the two DateTime objects has a floating time zone, it will first be converted to the
           time zone of the other object. This is what you want most of the time, but it can lead to
           inconsistent results when you compare a number of DateTime objects, some of which are floating,
           and some of which are in other time zones.

           If you want to have consistent results (because you want to sort a number of objects, for
           example), you can use the "compare_ignore_floating()" method:

             @dates = sort { DateTime->compare_ignore_floating($a, $b) } @dates;

           In this case, objects with a floating time zone will be sorted as if they were UTC times.

           Since DateTime objects overload comparison operators, this:

             @dates = sort @dates;

           is equivalent to this:

             @dates = sort { DateTime->compare($a, $b) } @dates;

           DateTime objects can be compared to any other calendar class that implements the
           "utc_rd_values()" method.

   How Datetime Math Works
       It's important to have some understanding of how datetime math is implemented in order to effectively
       use this module and "DateTime::Duration".

       Making Things Simple

       If you want to simplify your life and not have to think too hard about the nitty-gritty of datetime
       math, I have several recommendations:

          use the floating time zone

           If you do not care about time zones or leap seconds, use the "floating" timezone:

             my $dt = DateTime->now( time_zone => 'floating' );

           Math done on two objects in the floating time zone produces very predictable results.

           Note that in most cases you will want to start by creating an object in a specific zone and then
           convert it to the floating time zone. When an object goes from a real zone to the floating zone,
           the time for the object remains the same.

           This means that passing the floating zone to a constructor may not do what you want.

             my $dt = DateTime->now( time_zone => 'floating' );

           is equivalent to

             my $dt = DateTime->now( time_zone => 'UTC' )->set_time_zone('floating');

           This might not be what you wanted. Instead, you may prefer to do this:

             my $dt = DateTime->now( time_zone => 'local' )->set_time_zone('floating');

          use UTC for all calculations

           If you do care about time zones (particularly DST) or leap seconds, try to use non-UTC time zones
           for presentation and user input only.  Convert to UTC immediately and convert back to the local
           time zone for presentation:

             my $dt = DateTime->new( %user_input, time_zone => $user_tz );
             $dt->set_time_zone('UTC');

             # do various operations - store it, retrieve it, add, subtract, etc.

             $dt->set_time_zone($user_tz);
             print $dt->datetime;

          math on non-UTC time zones

           If you need to do date math on objects with non-UTC time zones, please read the caveats below
           carefully. The results "DateTime.pm" produces are predictable and correct, and mostly intuitive,
           but datetime math gets very ugly when time zones are involved, and there are a few strange corner
           cases involving subtraction of two datetimes across a DST change.

           If you can always use the floating or UTC time zones, you can skip ahead to Leap Seconds and Date
           Math

          date vs datetime math

           If you only care about the date (calendar) portion of a datetime, you should use either
           "delta_md()" or "delta_days()", not "subtract_datetime()". This will give predictable,
           unsurprising results, free from DST-related complications.

          subtract_datetime() and add_duration()

           You must convert your datetime objects to the UTC time zone before doing date math if you want to
           make sure that the following formulas are always true:

             $dt2 - $dt1 = $dur
             $dt1 + $dur = $dt2
             $dt2 - $dur = $dt1

           Note that using "delta_days" ensures that this formula always works, regardless of the timezone
           of the objects involved, as does using "subtract_datetime_absolute()". Other methods of
           subtraction are not always reversible.

       Adding a Duration to a Datetime

       The parts of a duration can be broken down into five parts. These are months, days, minutes, seconds,
       and nanoseconds. Adding one month to a date is different than adding 4 weeks or 28, 29, 30, or 31
       days.  Similarly, due to DST and leap seconds, adding a day can be different than adding 86,400
       seconds, and adding a minute is not exactly the same as 60 seconds.

       We cannot convert between these units, except for seconds and nanoseconds, because there is no fixed
       conversion between the two units, because of things like leap seconds, DST changes, etc.

       "DateTime.pm" always adds (or subtracts) days, then months, minutes, and then seconds and
       nanoseconds. If there are any boundary overflows, these are normalized at each step. For the days and
       months the local (not UTC) values are used. For minutes and seconds, the local values are used. This
       generally just works.

       This means that adding one month and one day to February 28, 2003 will produce the date April 1,
       2003, not March 29, 2003.

         my $dt = DateTime->new( year => 2003, month => 2, day => 28 );

         $dt->add( months => 1, days => 1 );

         # 2003-04-01 - the result

       On the other hand, if we add months first, and then separately add days, we end up with March 29,
       2003:

         $dt->add( months => 1 )->add( days => 1 );

         # 2003-03-29

       We see similar strangeness when math crosses a DST boundary:

         my $dt = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 5,
             hour      => 1,
             minute    => 58,
             time_zone => "America/Chicago",
         );

         $dt->add( days => 1, minutes => 3 );
         # 2003-04-06 02:01:00

         $dt->add( minutes => 3 )->add( days => 1 );
         # 2003-04-06 03:01:00

       Note that if you converted the datetime object to UTC first you would get predictable results.

       If you want to know how many seconds a duration object represents, you have to add it to a datetime
       to find out, so you could do:

        my $now = DateTime->now( time_zone => 'UTC' );
        my $later = $now->clone->add_duration($duration);

        my $seconds_dur = $later->subtract_datetime_absolute($now);

       This returns a duration which only contains seconds and nanoseconds.

       If we were add the duration to a different datetime object we might get a different number of
       seconds.

       DateTime::Duration supports three different end-of-month algorithms for adding months. This comes
       into play when an addition results in a day past the end of the month (for example, adding one month
       to January 30).

        # 2010-08-31 + 1 month = 2010-10-01
        $dt->add( months => 1, end_of_month => 'wrap' );

        # 2010-01-30 + 1 month = 2010-02-28
        $dt->add( months => 1, end_of_month => 'limit' );

        # 2010-04-30 + 1 month = 2010-05-31
        $dt->add( months => 1, end_of_month => 'preserve' );

       By default, it uses "wrap" for positive durations and "preserve" for negative durations. See
       DateTime::Duration for a detailed explanation of these algorithms.

       If you need to do lots of work with durations, take a look at Rick Measham's
       "DateTime::Format::Duration" module, which lets you present information from durations in many useful
       ways.

       There are other subtract/delta methods in DateTime.pm to generate different types of durations. These
       methods are "subtract_datetime()", "subtract_datetime_absolute()", "delta_md()", "delta_days()", and
       "delta_ms()".

       Datetime Subtraction

       Date subtraction is done solely based on the two object's local datetimes, with one exception to
       handle DST changes. Also, if the two datetime objects are in different time zones, one of them is
       converted to the other's time zone first before subtraction. This is best explained through examples:

       The first of these probably makes the most sense:

         my $dt1 = DateTime->new(
             year      => 2003,
             month     => 5,
             day       => 6,
             time_zone => 'America/Chicago',
         );

         # not DST

         my $dt2 = DateTime->new(
             year      => 2003,
             month     => 11,
             day       => 6,
             time_zone => 'America/Chicago',
         );

         # is DST

         my $dur = $dt2->subtract_datetime($dt1);
         # 6 months

       Nice and simple.

       This one is a little trickier, but still fairly logical:

         my $dt1 = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 5,
             hour      => 1,
             minute    => 58,
             time_zone => "America/Chicago",
         );

         # is DST

         my $dt2 = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 7,
             hour      => 2,
             minute    => 1,
             time_zone => "America/Chicago",
         );

         # not DST

         my $dur = $dt2->subtract_datetime($dt1);

         # 2 days and 3 minutes

       Which contradicts the result this one gives, even though they both make sense:

         my $dt1 = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 5,
             hour      => 1,
             minute    => 58,
             time_zone => "America/Chicago",
         );

         # is DST

         my $dt2 = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 6,
             hour      => 3,
             minute    => 1,
             time_zone => "America/Chicago",
         );

         # not DST

         my $dur = $dt2->subtract_datetime($dt1);

         # 1 day and 3 minutes

       This last example illustrates the "DST" exception mentioned earlier.  The exception accounts for the
       fact 2003-04-06 only lasts 23 hours.

       And finally:

         my $dt2 = DateTime->new(
             year      => 2003,
             month     => 10,
             day       => 26,
             hour      => 1,
             time_zone => 'America/Chicago',
         );

         my $dt1 = $dt2->clone->subtract( hours => 1 );

         my $dur = $dt2->subtract_datetime($dt1);
         # 60 minutes

       This seems obvious until you realize that subtracting 60 minutes from $dt2 in the above example still
       leaves the clock time at "01:00:00". This time we are accounting for a 25 hour day.

       Reversibility

       Date math operations are not always reversible. This is because of the way that addition operations
       are ordered. As was discussed earlier, adding 1 day and 3 minutes in one call to "add()" is not the
       same as first adding 3 minutes and 1 day in two separate calls.

       If we take a duration returned from "subtract_datetime()" and then try to add or subtract that
       duration from one of the datetimes we just used, we sometimes get interesting results:

         my $dt1 = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 5,
             hour      => 1,
             minute    => 58,
             time_zone => "America/Chicago",
         );

         my $dt2 = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 6,
             hour      => 3,
             minute    => 1,
             time_zone => "America/Chicago",
         );

         my $dur = $dt2->subtract_datetime($dt1);
         # 1 day and 3 minutes

         $dt1->add_duration($dur);
         # gives us $dt2

         $dt2->subtract_duration($dur);
         # gives us 2003-04-05 02:58:00 - 1 hour later than $dt1

       The "subtract_dauration()" operation gives us a (perhaps) unexpected answer because it first
       subtracts one day to get 2003-04-05T03:01:00 and then subtracts 3 minutes to get the final result.

       If we explicitly reverse the order we can get the original value of $dt1. This can be facilitated by
       "DateTime::Duration"'s "calendar_duration()" and "clock_duration()" methods:

         $dt2->subtract_duration( $dur->clock_duration )
             ->subtract_duration( $dur->calendar_duration );

       Leap Seconds and Date Math

       The presence of leap seconds can cause even more anomalies in date math. For example, the following
       is a legal datetime:

         my $dt = DateTime->new(
             year      => 1972,
             month     => 12,
             day       => 31,
             hour      => 23,
             minute    => 59,
             second    => 60,
             time_zone => 'UTC'
         );

       If we do the following:

        $dt->add( months => 1 );

       Then the datetime is now "1973-02-01 00:00:00", because there is no 23:59:60 on 1973-01-31.

       Leap seconds also force us to distinguish between minutes and seconds during date math. Given the
       following datetime:

         my $dt = DateTime->new(
             year      => 1972,
             month     => 12,
             day       => 31,
             hour      => 23,
             minute    => 59,
             second    => 30,
             time_zone => 'UTC'
         );

       we will get different results when adding 1 minute than we get if we add 60 seconds. This is because
       in this case, the last minute of the day, beginning at 23:59:00, actually contains 61 seconds.

       Here are the results we get:

         # 1972-12-31 23:59:30 - our starting datetime

         $dt->clone->add( minutes => 1 );
         # 1973-01-01 00:00:30 - one minute later

         $dt->clone->add( seconds => 60 );
         # 1973-01-01 00:00:29 - 60 seconds later

         $dt->clone->add( seconds => 61 );
         # 1973-01-01 00:00:30 - 61 seconds later

       Local vs. UTC and 24 hours vs. 1 day

       When math crosses a daylight saving boundary, a single day may have more or less than 24 hours.

       For example, if you do this:

         my $dt = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 5,
             hour      => 2,
             time_zone => 'America/Chicago',
         );

         $dt->add( days => 1 );

       then you will produce an invalid local time, and therefore an exception will be thrown.

       However, this works:

         my $dt = DateTime->new(
             year      => 2003,
             month     => 4,
             day       => 5,
             hour      => 2,
             time_zone => 'America/Chicago',
         );

         $dt->add( hours => 24 );

       and produces a datetime with the local time of "03:00".

       If all this makes your head hurt, there is a simple alternative. Just convert your datetime object to
       the "UTC" time zone before doing date math on it, and switch it back to the local time zone
       afterwards.  This avoids the possibility of having date math throw an exception, and makes sure that
       1 day equals 24 hours. Of course, this may not always be desirable, so caveat user!

   Overloading
       This module explicitly overloads the addition (+), subtraction (-), string and numeric comparison
       operators. This means that the following all do sensible things:

         my $new_dt = $dt + $duration_obj;

         my $new_dt = $dt - $duration_obj;

         my $duration_obj = $dt - $new_dt;

         foreach my $dt ( sort @dts ) { ... }

       Additionally, the fallback parameter is set to true, so other derivable operators (+=, -=, etc.) will
       work properly. Do not expect increment (++) or decrement (--) to do anything useful.

       The string comparison operators, "eq" or "ne", will use the string value to compare with non-DateTime
       objects.

       DateTime objects do not have a numeric value, using "==" or "<=>" to compare a DateTime object with a
       non-DateTime object will result in an exception. To safely sort mixed DateTime and non-DateTime
       objects, use "sort { $a cmp $b } @dates".

       The module also overloads stringification using the object's formatter, defaulting to "iso8601()"
       method. See "Formatters And Stringification" for details.

   Formatters And Stringification
       You can optionally specify a "formatter", which is usually a DateTime::Format::* object/class, to
       control the stringification of the DateTime object.

       Any of the constructor methods can accept a formatter argument:

         my $formatter = DateTime::Format::Strptime->new(...);
         my $dt = DateTime->new(year => 2004, formatter => $formatter);

       Or, you can set it afterwards:

         $dt->set_formatter($formatter);
         $formatter = $dt->formatter();

       Once you set the formatter, the overloaded stringification method will use the formatter. If
       unspecified, the "iso8601()" method is used.

       A formatter can be handy when you know that in your application you want to stringify your DateTime
       objects into a special format all the time, for example to a different language.

       If you provide a formatter class name or object, it must implement a "format_datetime" method. This
       method will be called with just the DateTime object as its argument.

   CLDR Patterns
       The CLDR pattern language is both more powerful and more complex than strftime. Unlike strftime
       patterns, you often have to explicitly escape text that you do not want formatted, as the patterns
       are simply letters without any prefix.

       For example, "yyyy-MM-dd" is a valid CLDR pattern. If you want to include any lower or upper case
       ASCII characters as-is, you can surround them with single quotes ('). If you want to include a single
       quote, you must escape it as two single quotes ('').

         'Today is ' EEEE
         'It is now' h 'o''clock' a

       Spaces and any non-letter text will always be passed through as-is.

       Many CLDR patterns which produce numbers will pad the number with leading zeroes depending on the
       length of the format specifier. For example, "h" represents the current hour from 1-12. If you
       specify "hh" then the 1-9 will have a leading zero prepended.

       However, CLDR often uses five of a letter to represent the narrow form of a pattern. This
       inconsistency is necessary for backwards compatibility.

       CLDR often distinguishes between the "format" and "stand-alone" forms of a pattern. The format
       pattern is used when the thing in question is being placed into a larger string. The stand-alone form
       is used when displaying that item by itself, for example in a calendar.

       It also often provides three sizes for each item, wide (the full name), abbreviated, and narrow. The
       narrow form is often just a single character, for example "T" for "Tuesday", and may not be unique.

       CLDR provides a fairly complex system for localizing time zones that we ignore entirely. The time
       zone patterns just use the information provided by "DateTime::TimeZone", and do not follow the CLDR
       spec.

       The output of a CLDR pattern is always localized, when applicable.

       CLDR provides the following patterns:

          G{1,3}

           The abbreviated era (BC, AD).

          GGGG

           The wide era (Before Christ, Anno Domini).

          GGGGG

           The narrow era, if it exists (and it mostly doesn't).

          y and y{3,}

           The year, zero-prefixed as needed. Negative years will start with a "-", and this will be
           included in the length calculation.

           In other, words the "yyyyy" pattern will format year -1234 as "-1234", not "-01234".

          yy

           This is a special case. It always produces a two-digit year, so "1976" becomes "76". Negative
           years will start with a "-", making them one character longer.

          Y{1,}

           The week of the year, from "$dt->week_year()".

          u{1,}

           Same as "y" except that "uu" is not a special case.

          Q{1,2}

           The quarter as a number (1..4).

          QQQ

           The abbreviated format form for the quarter.

          QQQQ

           The wide format form for the quarter.

          q{1,2}

           The quarter as a number (1..4).

          qqq

           The abbreviated stand-alone form for the quarter.

          qqqq

           The wide stand-alone form for the quarter.

          M{1,2]

           The numerical month.

          MMM

           The abbreviated format form for the month.

          MMMM

           The wide format form for the month.

          MMMMM

           The narrow format form for the month.

          L{1,2]

           The numerical month.

          LLL

           The abbreviated stand-alone form for the month.

          LLLL

           The wide stand-alone form for the month.

          LLLLL

           The narrow stand-alone form for the month.

          w{1,2}

           The week of the year, from "$dt->week_number()".

          W

           The week of the month, from "$dt->week_of_month()".

          d{1,2}

           The numeric day of of the month.

          D{1,3}

           The numeric day of of the year.

          F

           The day of the week in the month, from "$dt->weekday_of_month()".

          g{1,}

           The modified Julian day, from "$dt->mjd()".

          E{1,3} and eee

           The abbreviated format form for the day of the week.

          EEEE and eeee

           The wide format form for the day of the week.

          EEEEE and eeeee

           The narrow format form for the day of the week.

          e{1,2}

           The local numeric day of the week, from 1 to 7. This number depends on what day is considered the
           first day of the week, which varies by locale. For example, in the US, Sunday is the first day of
           the week, so this returns 2 for Monday.

          c

           The numeric day of the week from 1 to 7, treating Monday as the first of the week, regardless of
           locale.

          ccc

           The abbreviated stand-alone form for the day of the week.

          cccc

           The wide stand-alone form for the day of the week.

          ccccc

           The narrow format form for the day of the week.

          a

           The localized form of AM or PM for the time.

          h{1,2}

           The hour from 1-12.

          H{1,2}

           The hour from 0-23.

          K{1,2}

           The hour from 0-11.

          k{1,2}

           The hour from 1-24.

          j{1,2}

           The hour, in 12 or 24 hour form, based on the preferred form for the locale. In other words, this
           is equivalent to either "h{1,2}" or "H{1,2}".

          m{1,2}

           The minute.

          s{1,2}

           The second.

          S{1,}

           The fractional portion of the seconds, rounded based on the length of the specifier. This
           returned without a leading decimal point, but may have leading or trailing zeroes.

          A{1,}

           The millisecond of the day, based on the current time. In other words, if it is 12:00:00.00, this
           returns 43200000.

          z{1,3}

           The time zone short name.

          zzzz

           The time zone long name.

          Z{1,3}

           The time zone offset.

          ZZZZ

           The time zone short name and the offset as one string, so something like "CDT-0500".

          v{1,3}

           The time zone short name.

          vvvv

           The time zone long name.

          V{1,3}

           The time zone short name.

          VVVV

           The time zone long name.

   strftime Patterns
       The following patterns are allowed in the format string given to the "$dt->strftime()" method:

          %a

           The abbreviated weekday name.

          %A

           The full weekday name.

          %b

           The abbreviated month name.

          %B

           The full month name.

          %c

           The default datetime format for the object's locale.

          %C

           The century number (year/100) as a 2-digit integer.

          %d

           The day of the month as a decimal number (range 01 to 31).

          %D

           Equivalent to %m/%d/%y. This is not a good standard format if you want folks from both the United
           States and the rest of the world to understand the date!

          %e

           Like %d, the day of the month as a decimal number, but a leading zero is replaced by a space.

          %F

           Equivalent to %Y-%m-%d (the ISO 8601 date format)

          %G

           The ISO 8601 year with century as a decimal number. The 4-digit year corresponding to the ISO
           week number (see %V). This has the same format and value as %Y, except that if the ISO week
           number belongs to the previous or next year, that year is used instead. (TZ)

          %g

           Like %G, but without century, i.e., with a 2-digit year (00-99).

          %h

           Equivalent to %b.

          %H

           The hour as a decimal number using a 24-hour clock (range 00 to 23).

          %I

           The hour as a decimal number using a 12-hour clock (range 01 to 12).

          %j

           The day of the year as a decimal number (range 001 to 366).

          %k

           The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a
           blank. (See also %H.)

          %l

           The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a
           blank. (See also %I.)

          %m

           The month as a decimal number (range 01 to 12).

          %M

           The minute as a decimal number (range 00 to 59).

          %n

           A newline character.

          %N

           The fractional seconds digits. Default is 9 digits (nanoseconds).

             %3N   milliseconds (3 digits)
             %6N   microseconds (6 digits)
             %9N   nanoseconds  (9 digits)

          %p

           Either `AM' or `PM' according to the given time value, or the corresponding strings for the
           current locale. Noon is treated as `pm' and midnight as `am'.

          %P

           Like %p but in lowercase: `am' or `pm' or a corresponding string for the current locale.

          %r

           The time in a.m. or p.m. notation. In the POSIX locale this is equivalent to `%I:%M:%S %p'.

          %R

           The time in 24-hour notation (%H:%M). (SU) For a version including the seconds, see %T below.

          %s

           The number of seconds since the epoch.

          %S

           The second as a decimal number (range 00 to 61).

          %t

           A tab character.

          %T

           The time in 24-hour notation (%H:%M:%S).

          %u

           The day of the week as a decimal, range 1 to 7, Monday being 1. See also %w.

          %U

           The week number of the current year as a decimal number, range 00 to 53, starting with the first
           Sunday as the first day of week 01. See also %V and %W.

          %V

           The ISO 8601:1988 week number of the current year as a decimal number, range 01 to 53, where week
           1 is the first week that has at least 4 days in the current year, and with Monday as the first
           day of the week. See also %U and %W.

          %w

           The day of the week as a decimal, range 0 to 6, Sunday being 0. See also %u.

          %W

           The week number of the current year as a decimal number, range 00 to 53, starting with the first
           Monday as the first day of week 01.

          %x

           The default date format for the object's locale.

          %X

           The default time format for the object's locale.

          %y

           The year as a decimal number without a century (range 00 to 99).

          %Y

           The year as a decimal number including the century.

          %z

           The time-zone as hour offset from UTC. Required to emit RFC822-conformant dates (using "%a, %d %b
           %Y %H:%M:%S %z").

          %Z

           The time zone or name or abbreviation.

          %%

           A literal `%' character.

          %{method}

           Any method name may be specified using the format "%{method}" name where "method" is a valid
           "DateTime.pm" object method.

   DateTime.pm and Storable
       DateTime implements Storable hooks in order to reduce the size of a serialized DateTime object.

THE DATETIME PROJECT ECOSYSTEM
       This module is part of a larger ecosystem of modules in the DateTime family.

   DateTime::Set
       The DateTime::Set module represents sets (including recurrences) of datetimes. Many modules return
       sets or recurrences.

   Format Modules
       The various format modules exist to parse and format datetimes. For example, DateTime::Format::HTTP
       parses dates according to the RFC 1123 format:

         my $datetime
             = DateTime::Format::HTTP->parse_datetime('Thu Feb  3 17:03:55 GMT 1994');

         print DateTime::Format::HTTP->format_datetime($datetime);

       Most format modules are suitable for use as a "formatter" with a DateTime object.

       All format modules start with "DateTime::Format::".

   Calendar Modules
       There are a number of modules on CPAN that implement non-Gregorian calendars, such as the Chinese,
       Mayan, and Julian calendars.

       All calendar modules start with "DateTime::Calendar::".

   Event Modules
       There are a number of modules that calculate the dates for events, such as Easter, Sunrise, etc.

       All event modules start with "DateTime::Event::".

   Others
       There are many other modules that work with DateTime, including modules in the "DateTimeX" namespace,
       as well as others.

       See the datetime wiki <http://datetime.perl.org> and search.cpan.org
       <http://search.cpan.org/search?query=datetime&mode=dist> for more details.

KNOWN BUGS
       The tests in 2_infinite.t seem to fail on some machines, particularly on Win32. This appears to be
       related to Perl's internal handling of IEEE infinity and NaN, and seems to be highly
       platform/compiler/phase of moon dependent.

       If you don't plan to use infinite datetimes you can probably ignore this. This will be fixed
       (perhaps) in future versions.

SUPPORT
       Support for this module is provided via the datetime@perl.org email list. See
       http://datetime.perl.org/wiki/datetime/page/Mailing_List for details.

       Please submit bugs to the CPAN RT system at http://rt.cpan.org/NoAuth/Bugs.html?Dist=DateTime or via
       email at bug-datetime@rt.cpan.org.

DONATIONS
       If you'd like to thank me for the work I've done on this module, please consider making a "donation"
       to me via PayPal. I spend a lot of free time creating free software, and would appreciate any support
       you'd care to offer.

       Please note that I am not suggesting that you must do this in order for me to continue working on
       this particular software. I will continue to do so, inasmuch as I have in the past, for as long as it
       interests me.

       Similarly, a donation made in this way will probably not make me work on this software much more,
       unless I get so many donations that I can consider working on free software full time, which seems
       unlikely at best.

       To donate, log into PayPal and send money to autarch@urth.org or use the button on this page:
       http://www.urth.org/~autarch/fs-donation.html <http://www.urth.org/~autarch/fs-donation.html>

SEE ALSO
       datetime@perl.org mailing list

       http://datetime.perl.org/

AUTHOR
       Dave Rolsky <autarch@urth.org>

COPYRIGHT AND LICENSE
       This software is Copyright (c) 2011 by Dave Rolsky.

       This is free software, licensed under:

         The Artistic License 2.0 (GPL Compatible)



perl v5.12.5                                     2013-08-25                                      DateTime(3)

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