README.md - metacpan.org

NAME

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

VERSION

version 1.86

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 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.

Special Case Platforms

If you are on the Win32 platform, you will want to also install
DateTime::TimeZone::Local::Win32. This will enable you to specify a
time zone of 'local' when creating a DateTime object.

If you are on HPUX, install DateTime::TimeZone::HPUX. This provides
support for HPUX style time zones like 'MET-1METDST'.

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.

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