How to format DateTimes as strings with Timex's DateFormat module, and time intervals with TimeFormatter
Formatting DateTimes in Timex is done via the Timex module. There are two built in formatters, :default and :strftime. The details of how to construct format strings can be found in the docs for Timex.Format.DateTime.Formatters.Default and Timex.Format.DateTime.Formatters.Strftime, so this document will be a brief overview of the DateFormat API and how you use it typically.
# By default the :default formatter is used
iex> Timex.format({2013,8,18}, "{YYYY}-{M}-{D}")
{:ok, "2013-8-18"}
# But you can use the :strftime formatter very easily
iex> Timex.format({2013,8,18}, "%Y-%m-%d", :strftime)
{:ok, "2013-08-18"}
# If you create your own formatter, you can use it easily as well
iex> Timex.format({2013,8,18}, format_str, MyApp.MyDateFormatter)
# If formatting fails for some reason you will get an `{:error, reason}` tuple, so it's
# recommended to use `format/1` or `format/2`; however you can use the "bang"
# versions of these two, `format!/1` or `format!/2` which will return the result directly,
# or raise on failure
iex> Timex.format!({2013,8,18}, "%Y-%m-%d", :strftime)
"2013-08-18"Formatting durations (or timestamps really) is done via the Timex.Format.Duration.Formatter module, or more commonly via Timex.format_duration. It is extensible like date/time formatting as well.
# Time since the epoch
iex> Duration.now |> Timex.format_duration
"P45Y7M25DT18H13M10.966072S"
iex> Duration.now |> Timex.format_duration(:humanized)
"45 years, 7 months, 3 weeks, 4 days, 18 hours, 13 minutes, 16 seconds, 141.422 milliseconds"
# Time it took to execute some code
iex> {interval, _} = Duration.measure(fn -> 1..10000 |> Enum.reverse end)
#<Duration(PT0.002614S)>
iex> interval |> Timex.format_duration
"PT0.002614S"
iex> interval |> Timex.format_duration(:humanized)
"2.614 milliseconds"