NAME
    DateTime::TimeZone - Time zone object base class and factory

VERSION
    version 1.62

SYNOPSIS
      use DateTime;
      use DateTime::TimeZone;

      my $tz = DateTime::TimeZone->new( name => 'America/Chicago' );

      my $dt = DateTime->now();
      my $offset = $tz->offset_for_datetime($dt);

DESCRIPTION
    This class is the base class for all time zone objects. A time zone is
    represented internally as a set of observances, each of which describes
    the offset from GMT for a given time period.

    Note that without the "DateTime.pm" module, this module does not do
    much. It's primary interface is through a "DateTime" object, and most
    users will not need to directly use "DateTime::TimeZone" methods.

USAGE
    This class has the following methods:

  DateTime::TimeZone->new( name => $tz_name )
    Given a valid time zone name, this method returns a new time zone
    blessed into the appropriate subclass. Subclasses are named for the
    given time zone, so that the time zone "America/Chicago" is the
    DateTime::TimeZone::America::Chicago class.

    If the name given is a "link" name in the Olson database, the object
    created may have a different name. For example, there is a link from the
    old "EST5EDT" name to "America/New_York".

    When loading a time zone from the Olson database, the constructor checks
    the version of the loaded class to make sure it matches the version of
    the current DateTime::TimeZone installation. If they do not match it
    will issue a warning. This is useful because time zone names may fall
    out of use, but you may have an old module file installed for that time
    zone.

    There are also several special values that can be given as names.

    If the "name" parameter is "floating", then a
    "DateTime::TimeZone::Floating" object is returned. A floating time zone
    does have *any* offset, and is always the same time. This is useful for
    calendaring applications, which may need to specify that a given event
    happens at the same *local* time, regardless of where it occurs. See RFC
    2445 for more details.

    If the "name" parameter is "UTC", then a "DateTime::TimeZone::UTC"
    object is returned.

    If the "name" is an offset string, it is converted to a number, and a
    "DateTime::TimeZone::OffsetOnly" object is returned.

   The "local" time zone
    If the "name" parameter is "local", then the module attempts to
    determine the local time zone for the system.

    The method for finding the local zone varies by operating system. See
    the appropriate module for details of how we check for the local time
    zone.

    *   DateTime::TimeZone::Local::Unix

    *   DateTime::TimeZone::Local::Win32

    *   DateTime::TimeZone::Local::VMS

    If a local time zone is not found, then an exception will be thrown.

  $tz->offset_for_datetime( $dt )
    Given a "DateTime" object, this method returns the offset in seconds for
    the given datetime. This takes into account historical time zone
    information, as well as Daylight Saving Time. The offset is determined
    by looking at the object's UTC Rata Die days and seconds.

  $tz->offset_for_local_datetime( $dt )
    Given a "DateTime" object, this method returns the offset in seconds for
    the given datetime. Unlike the previous method, this method uses the
    local time's Rata Die days and seconds. This should only be done when
    the corresponding UTC time is not yet known, because local times can be
    ambiguous due to Daylight Saving Time rules.

  $tz->is_dst_for_datetime( $dt )
    Given a "DateTime" object, this method returns true if the DateTime is
    currently in Daylight Saving Time.

  $tz->name
    Returns the name of the time zone.

  $tz->short_name_for_datetime( $dt )
    Given a "DateTime" object, this method returns the "short name" for the
    current observance and rule this datetime is in. These are names like
    "EST", "GMT", etc.

    It is strongly recommended that you do not rely on these names for
    anything other than display. These names are not official, and many of
    them are simply the invention of the Olson database maintainers.
    Moreover, these names are not unique. For example, there is an "EST" at
    both -0500 and +1000/+1100.

  $tz->is_floating
    Returns a boolean indicating whether or not this object represents a
    floating time zone, as defined by RFC 2445.

  $tz->is_utc
    Indicates whether or not this object represents the UTC (GMT) time zone.

  $tz->has_dst_changes
    Indicates whether or not this zone has *ever* had a change to and from
    DST, either in the past or future.

  $tz->is_olson
    Returns true if the time zone is a named time zone from the Olson
    database.

  $tz->category
    Returns the part of the time zone name before the first slash. For
    example, the "America/Chicago" time zone would return "America".

  DateTime::TimeZone->is_valid_name($name)
    Given a string, this method returns a boolean value indicating whether
    or not the string is a valid time zone name. If you are using
    "DateTime::TimeZone::Alias", any aliases you've created will be valid.

  DateTime::TimeZone->all_names
    This returns a pre-sorted list of all the time zone names. This list
    does not include link names. In scalar context, it returns an array
    reference, while in list context it returns an array.

  DateTime::TimeZone->categories
    This returns a list of all time zone categories. In scalar context, it
    returns an array reference, while in list context it returns an array.

  DateTime::TimeZone->links
    This returns a hash of all time zone links, where the keys are the old,
    deprecated names, and the values are the new names. In scalar context,
    it returns a hash reference, while in list context it returns a hash.

  DateTime::TimeZone->names_in_category( $category )
    Given a valid category, this method returns a list of the names in that
    category, without the category portion. So the list for the "America"
    category would include the strings "Chicago", "Kentucky/Monticello", and
    "New_York". In scalar context, it returns an array reference, while in
    list context it returns an array.

  DateTime::TimeZone->countries()
    Returns a sorted list of all the valid country codes (in lower-case)
    which can be passed to "names_in_country()". In scalar context, it
    returns an array reference, while in list context it returns an array.

    If you need to convert country codes to names or vice versa you can use
    "Locale::Country" to do so.

  DateTime::TimeZone->names_in_country( $country_code )
    Given a two-letter ISO3166 country code, this method returns a list of
    time zones used in that country. The country code may be of any case. In
    scalar context, it returns an array reference, while in list context it
    returns an array.

    This list is returned in an order vaguely based on geography and
    population. In general, the least used zones come last, but there are
    not guarantees of a specific order from one release to the next. This
    order is probably the best option for presenting zones names to end
    users.

  DateTime::TimeZone->offset_as_seconds( $offset )
    Given an offset as a string, this returns the number of seconds
    represented by the offset as a positive or negative number. Returns
    "undef" if $offset is not in the range "-99:59:59" to "+99:59:59".

    The offset is expected to match either
    "/^([\+\-])?(\d\d?):(\d\d)(?::(\d\d))?$/" or
    "/^([\+\-])?(\d\d)(\d\d)(\d\d)?$/". If it doesn't match either of these,
    "undef" will be returned.

    This means that if you want to specify hours as a single digit, then
    each element of the offset must be separated by a colon (:).

  DateTime::TimeZone->offset_as_string( $offset )
    Given an offset as a number, this returns the offset as a string.
    Returns "undef" if $offset is not in the range -359999 to 359999.

  Storable Hooks
    This module provides freeze and thaw hooks for "Storable" so that the
    huge data structures for Olson time zones are not actually stored in the
    serialized structure.

    If you subclass "DateTime::TimeZone", you will inherit its hooks, which
    may not work for your module, so please test the interaction of your
    module with Storable.

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/ReportBug.html?Queue=datetime%3A%3Atimezone or
    via email at bug-datetime-timezone@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>

CREDITS
    This module was inspired by Jesse Vincent's work on
    Date::ICal::Timezone, and written with much help from the
    datetime@perl.org list.

SEE ALSO
    datetime@perl.org mailing list

    http://datetime.perl.org/

    The tools directory of the DateTime::TimeZone distribution includes two
    scripts that may be of interest to some people. They are parse_olson and
    tests_from_zdump. Please run them with the --help flag to see what they
    can be used for.

AUTHOR
    Dave Rolsky <autarch@urth.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2013 by Dave Rolsky.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

