Question 1

How to format dates in Elixir with strftime?

Accepted Answer

Use Calendar's Strftime module, which supports strftime patterns and validates input types. For example, `Calendar.Date.from_erl!({2014,9,6}) |> Calendar.Strftime.strftime "%a %d.%m.%y"` returns {:ok, "Sat 06.09.14"}, and it errors if the type lacks required data.

Question 2

Calendar vs Elixir standard library DateTime: which is better for timezones?

Accepted Answer

Calendar offers advanced formatting and polymorphic protocols, while Elixir's standard library with tzdata handles basic timezone conversions since version 1.8. Choose Calendar if you need strftime or complex interoperability; otherwise, the standard library suffices to reduce dependencies.

Question 3

How to convert Erlang tuples to Elixir datetime with a timezone?

Accepted Answer

Use `Calendar.DateTime.from_erl/2` with a timezone string. For instance, `Calendar.DateTime.from_erl {{2014,10,4},{23,44,32}}, "America/Montevideo"` returns a DateTime struct, and you can shift zones with `shift_zone!`.

Question 4

Does Calendar parse ISO 8601 strings reliably?

Accepted Answer

Yes, Calendar parses ISO 8601 and RFC 3339 formats with functions like `Calendar.DateTime.Parse.rfc3339_utc` for UTC timestamps. It handles microseconds and timezone offsets, ensuring accurate datetime representations.

Question 5

What timezone database does Calendar use and how to update it?

Accepted Answer

Calendar uses the tzdata library, which provides IANA timezone data. Updates are managed through the tzdata package via Hex, and you may need to add it to your application list in mix.exs to avoid ets lookup errors.

Question 6

How does Calendar handle daylight saving time changes?

Accepted Answer

Through tzdata integration, Calendar automatically accounts for DST transitions when performing timezone shifts or operations. For example, shifting a DateTime between zones adjusts offsets based on the timezone rules in the database.

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