til/elixir/check-list-membership.md

Check List Membership

You can use the in operator to check if something appears in a list. This is a handy way of checking if a variable is one of a few acceptable or expected values.

For instance, a common DateTime comparison pattern relies on this to check if a DateTime is >= or <= to another DateTime.

{:ok, datetime} = DateTime.from_naive(~N[2016-05-24 13:26:08.003], "Etc/UTC")

DateTime.compare(datetime, DateTime.utc_now()) in [:lt, :eq]

Alternatively, you can check that something does not have membership in a list by also including the not operator.

DateTime.compare(datetime, DateTime.utc_now()) not in [:lt, :eq]