On Thu, Dec 3, 2020 at 4:02 PM J. Lewis Muir <[email protected]> wrote:
> 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
>
>
That's Date#new_offset, not DateTime#new_offset. See
https://github.com/ruby/ruby/blob/ruby_2_0_0/ext/date/date_core.c#L9629
Thanks,
Jeremy
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