TimeZoneInfo

Time zone support for Elixir by using the IANA Time Zone Database.

Installation

The package can be installed by adding time_zone_info to your list of dependencies in mix.exs:

def deps do
  [
    {:time_zone_info, "~> 0.7"}
  ]
end

Usage

After installation, TimeZoneInfo can be used as follows.

iex> TimeZoneInfo.iana_version
"2024a"
iex> TimeZoneInfo.time_zones() |> Enum.take(3)
["Africa/Abidjan", "Africa/Accra", "Africa/Addis_Ababa"]
iex> TimeZoneInfo.TimeZoneDatabase.time_zone_periods_from_wall_datetime(~N[2021-09-23 09:56:00], "Europe/Berlin")
{:ok,
 %{
   std_offset: 3600,
   utc_offset: 3600,
   wall_period: {~N[2021-03-28 03:00:00], ~N[2021-10-31 03:00:00]},
   zone_abbr: "CEST"
 }}

In combination with DateTime and Calendar:

iex> {:ok, berlin} = DateTime.from_naive(
...>   ~N[2020-03-29 01:30:00],
...>   "Europe/Berlin",
...>    TimeZoneInfo.TimeZoneDatabase)
{:ok, #DateTime<2020-03-29 01:30:00+01:00 CET Europe/Berlin>}
iex> Calendar.put_time_zone_database(TimeZoneInfo.TimeZoneDatabase)
:ok
iex> DateTime.shift_zone(berlin, "America/New_York")
{:ok, #DateTime<2020-03-28 20:30:00-04:00 EDT America/New_York>}

Instead of the line Calendar.put_time_zone_database(TimeZoneInfo.TimeZoneDatabase) you can also specify the following entry in the configuration.

config :elixir, :time_zone_database, TimeZoneInfo.TimeZoneDatabase

Config

TimeZoneInfo has several configuration options:

• Enable automated updates from the IANA tzdb
• Setup for how many years rules will be precalculated
• Selection of supported time zones

For more information how to configure TimeZoneInfo see Config.

Default Time Zone Data

The default configuration of TimeZoneInfo is update: :disabled. In this case, the IANA database in version 2024a with a lookahead of 15 years is in use.

If a time zone has continuation rules, the periods after the lookahead are calculating by these rules. Note, these calculations are much more expensive as the determination of periods inside the prepared time span.

Benchmarks

The benchmarks can be executed with mix bench.

Benchmarks:

• This benchmark compares TimeZoneInfo with Tzdata, Tz and Zoneinfo.

• This benchmark compares the different TimeZoneInfo.DataStores.

• This benchmark measures the speed of transforming the raw IANA data to the required format at runtime.

Differences to Tzdata and Tz

There are some differences to Tzdata and Tz. The list shows differences to Tzdata and/or Tz.

• Use of :persitent_term with an optional use of :ets.
• Persisting data in External Term Format
• The data persisting is customizable by the behaviour TimeZoneInfo.DataPersistence.
• Optional download of time zone data in TimeZoneInfo format.
• The download is customizable by the behaviour TimeZoneInfo.Downloader.
• Filter time zones per config.
• Optional listener that will be called on updates.
• TimeZoneInfo calculates periods in the far future by continuation rules. Except for time zones that have daylight saving times for Ramadan.

References

The home of the IANA Time Zone Database: https://www.iana.org/time-zones

Links:

• Time zone - Wikipedia
• timeanddate.com
• WorldTimeServer.com

Other Elixir implementations:

• tzdata - Tzdata is a parser and library for the tz database.
• tz - Time zone support for Elixir
• zoneinfo - Elixir time zone support for your OS-supplied zoneinfo files

Other implementations:

• DateTime::TimeZone - Perl
  • TimeZoneInfo use this module as a checker in the tests.
• NodaTime - A better date and time API for .NET
  • TimeZonInfo use some data from this site in the tests.