Re: Ada.Calendar.Formatting.Image (or Time_Of) changing the time

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2020-03-03 13:59, Marius Amado-Alves wrote:

> Thanks. I used the default, which is a zero offset, hence my surprise,

Zero means UTC, AFAIK. To get local time you should pass the result of 
UTC_Time_Offset from Ada.Calendar.Time_Zones.

> but maybe I am misunderstanding something, date and time is such a complex matter.

Nothing complex, just messed up. The design as I understand it, because 
ARM tells nothing about the meaning of Time values, is that you 
interpret the value of Time differently in different time zones. It is 
done by passing the time zone offset, which itself is a function of time 
to add necessary confusion. So Time is kind of simultaneously UTC and 
CET and whatever.

The common, sane (and scientific) understanding is that UTC and CET are 
different times.

One of the consequences of present design is that you, for example, 
could not store local time reading as a compound value. Without a time 
offset it has no sense. You also cannot spell Jan 23, 2100 CET, as you 
do not know which time offset it will possibly have in 80 years. CET is 
a function and not a value. So there is a date and no time.

> (Namely, I dont understand how a "fixed" offset can vary throughout the year.)

Political time jumps twice a year, so the offset does. Formally these 
are two different times, e.g. CET and CEST.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de