Using Date - Ruby vs. Rails

This little investigation was prompted by an interesting quirk whereby Date.today == Date.tomorrow returned true.

Date.today is implemented in Ruby and uses system’s local time & timezone.

In Rails, timezone can be set in config/application.rb but defaults to UTC. Thus, it can be different that local system time used by Ruby.

Date.tomorrow & Date.yesterday are implemented in Rails and use Date.current internally.

Date.current is implemented in Rails thus:

::Time.zone ? ::Time.zone.today : ::Date.today

i.e. if Time.zone is set (which in Rails it is, as stated above), Date.current, Date.tomorrow & Date.yesterday will use Time.zone.today. If it’s not set, which never happens in Rails, then the methods fall back to the timezone-unaware Ruby implementation.

The solution to avoiding issues related to all this in Rails is to use the Rails implementations based on Date.current and avoid using Ruby’s Date.today.