I've been using ruby for years, but I've never had a good use for DateTime. Since there's so much discussion about it recently, maybe I could ask again, why does it exist? I always avoid using DateTime because: 1. It looks like a Time, but behaves like a Date: plus_one_sec = Time.now + 1 plus_one_day = DateTime.now + 1 If it's really meant to be a Date plus fractional values for the time of day, then I think it should ignore time zones and utc offset completely because it's ambiguous. Date does not have a zone: only when you compare times should you compare zones. 2. It ignores tzinfo, so moving over daylight savings time doesn't change the offset: winter_time = Time.local(2014, 3, 9) summer_time = winter_time + (24 * 60 * 60) winter_time.zone #=> "PST" summer_time.zone #=> "PDT" winter_dt = winter_time.to_datetime summer_dt = winter_dt + 1 winter_dt.zone #=> "-08:00" summer_dt.zone #=> "-08:00" Here, +1 adds 24 hours to the local time, when the actual difference should be 23 (with the offset change). 3. Its "zone" has no useful value. dt = DateTime.new(2012,12,6, 1, 0, 0, "-07:00") dt.zone # => "-07:00" dt.utc? # => NoMethodError: undefined method `utc?' dt.dst? # => NoMethodError: undefined method `dst?' dt.utc_offset # => NoMethodError: undefined method `utc_offset' I'm not sure what to think of the "%s %z" patch for DateTime.strptime since I never use it. It makes sense that it should be consistent with Time, but maybe DateTime itself is wrong-headed to begin with? Andrew Vit
on 2014-05-04 23:04
on 2014-05-04 23:26
It's like a slower version of Time, written in pure Ruby, for people who hate speed
on 2014-05-05 00:04
On Sun, May 4, 2014 at 4:24 PM, Tony Arcieri <email@example.com> wrote: > It's like a slower version of Time, written in pure Ruby, for people who > hate speed Pure Ruby? ext/date/date_core.c ext/date/date_parse.c ext/date/date_strftime.c ext/date/date_strptime.c ext/date/date_tmx.h ext/date/depend ext/date/extconf.rb ext/date/lib/date.rb ext/date/lib/date/format.rb It seems to me there's more Ruby code in lib/time.rb than in ext/date/lib/date.rb. That said, I do not understand why have both Time and DateTime.
on 2014-05-05 04:51
Andrew Vit wrote in post #1144945: > , why does it exist? I agree with the sentiment of always avoiding it. re: pure ruby, it was https://github.com/ruby/ruby/blob/v1_8_7_374/lib/d... it isn't anymore https://github.com/ruby/ruby/blob/trunk/ext/date/d... On Rogues Parley you once linked to http://stackoverflow.com/questions/5941613/are-the... which linked to https://www.ruby-forum.com/topic/146117#646897 Stefan Rusterholz (apeiros) on 2008-03-16 02:05 > Time is a wrapper around Unix-Epoch. > Date (and DateTime) use rational and a "day zero" for storage. So Time is faster but the upper and lower bounds are tied to epoch time (which for 32bit epoch times is something around 1970-2040 - not even enough to represent the birthday of my parents) while Date (and DateTime) have an almost infinite range but are *terribly* slow The pickaxe Ruby says: > The date library implements classes Date and DateTime, which provide a comprehensive set of facilities for storing, manipulating, and converting dates with or without time components. The classes can represent and manipulate civil, ordinal, commercial, Julian, and standard dates, starting January 1, 4713 BCE. The DateTime class extends Date with hours, minutes, seconds, and fractional seconds, and it provides some support for time zones. The classes also provide support for parsing and formatting date and datetime strings. It appears this date/datetime code was written by Tadayoshi Funaba 1998-present and documented by William Webber I didn't see any benchmarks in trunk about speed increases, but I didn't look very carefully. -Benjamin