On Thursday, December 3, 2020 at 1:33:42 PM UTC-6 Jeremy Evans wrote:
> On Thu, Dec 3, 2020 at 11:03 AM J. Lewis Muir wrote:
>
>> On Thursday, December 3, 2020 at 12:00:20 AM UTC-6 Jeremy Evans wrote:
>>
>>> If you can use Ruby 2.0, you should be able to easily use the mysql
>>> gem. Current Sequel runs fine on Ruby 2.0. You will have to switch to
>>> Sequel.datetime_class = DateTime, though, because timezone support was not
>>> added to Time until Ruby 2.6.
>>>
>>
>> I understand that time zone support was only added to Time in Ruby 2.6,
>> but for Ruby 2.0, I don't understand how DateTime is able to handle time
>> zones any better than Time. I don't see any support for named time zones
>> in Time nor DateTime as of Ruby 2.0; I just see support for a UTC offset.
>> So, I'm not understanding the need for Sequel.datetime_class = DateTime.
>> Could you explain?
>>
>
> Before Ruby 2.6, Time didn't handle timezones, and you can't take an
> existing Time instance and convert it to a new timezone offset (unlike with
> DateTime). You could only convert it from local to utc or vice versa.
>
> Before Ruby 2.2, Time cannot even deal with parsed times not in the local
> zone:
>
> $ruby21 -rtime -e 'p Time.parse("2020-10-20 10:20:30-03:00")'
> 2020-10-20 06:20:30 -0700
> $ ruby22 -rtime -e 'p Time.parse("2020-10-20 10:20:30-03:00")'
> 2020-10-20 10:20:30 -0300
>
> DateTime itself doesn't handle timezones in any version, but Sequel can
> use TZInfo to figure out the correct offset, and use
> DateTime's offset support to set the offset correctly. Sequel can't do
> that with Time, since Time doesn't have support for it.
>
Thank you for the explanation! I looked at Sequel's
lib/sequel/timezones.rb, and I see it using DateTime#new_offset. I had no
idea this would work in Ruby 2.0 because that instance method does not
exist in the docs:
* https://ruby-doc.org/stdlib-2.0.0/libdoc/date/rdoc/DateTime.html
* https://ruby-doc.org/stdlib-2.0.0/libdoc/date/rdoc/Date.html
But it's listed in "DateTime.instance_methods", and "ri
DateTime.new_offset" knows about it. Looking at the Ruby source, if I'm
reading it right, that method is private in Ruby 2.0:
https://github.com/ruby/ruby/blob/ruby_2_0_0/ext/date/date_core.c#L9523
I guess that would explain why it was not in the docs.
Thanks!
Lewis
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