In Elixir, function DateTime.add/3 is missing. There are Date.add/2, NaiveDateTime.add/3, and Time.add/3. But only DateTime has no add/3 function. Is there any reason? Maybe because of time zone related problem? As as walkaround, I’ve convert it to Unix time |> shift time, then compare with anothe…

[image] jung-hunsoo: I hope Elixir be more developer-friendly so that more dev guys gather. But sometimes I got confused which the Elixir is aimed at; Popular usage or Sophisticated purposes. It’s not about popular or sophisticated, but rather about correctness vs. full of edge-case issues. E…

[image] jung-hunsoo: I think DateTime.add/3 can be achieved by using both DateTime.from_unix/3 and DateTime.to_unix/2. Is there any enhancement for this function? That’s the misconception here. That does not work at all because unix timestamps don’t deal with timezones (e.g. switch from/to da…

If I understand you correctly, for round trip timing (as in rpc) it’s safer to use monotonic time. Otherwise you can get negative or skewed results if the underlying OS decides to change its time while the request is in-flight.

It’ll still not consider leap-seconds but that might be ok for your application.

@LostKobrakai is completely right. What do you require the timestamps for? There are two reasons why the calendar- and timezone-related stuff is not part of the Elixir standard library: it greatly increases the size of the stdlib, which is a problem in embedded contexts. Time zone information fr…

Thanks for the relies. I can understand and agree the various opinions. I’m currently using Unix time for hours shift. And my ecto schema holds three fields; d_day_local :naive_datetime, d_day_utc :utc_datetime, time_zone :string. Calendar is in a dependencies to do this. Dealing with time zone an…

Example from another language: Python doesn’t offer nearly any timezone handling capabilities out of the box. Usually you install pytz to deal with timezones. So in that regard, I don’t think of Elixir’s choice as odd in any way.

In js, Date instance can be easily traveled via .setHours() method. I can now understand why now/3 is missing in DateTime module. Nevertheless we can think providing utc_time_travel method, which will be like a utc_offset.

Changing to fixed values is still vastly different to adding/substracting time from dates. One does only need to validate a datetime on it’s own, while the other does need to make sure the time difference is calculated correctly to the resulting datetime. The latter is certainly more prone to issues…

Thanks. I’ve read that post before. That’s why I implemented d_day_local (naive), d_day_utc (utc), and timezone (string), as well as Calendar package for timezone db.

Elixir Programming Language Forum

DateTime.add/3 is missing

Questions & Help Questions

mbuhot April 12, 2018, 7:26am 3

The round trip via unix timestamp should be fine for UTC date times right?