Re: [Boost-users] [date_time] timezone rules for different years

From: Jeff Garland (jeff_at_[hidden])
Date: 2007-01-10 11:39:32

Stephen Turner wrote:
>> -----Original Message-----
>> Date: Wed, 10 Jan 2007 08:12:18 -0700
>> From: Jeff Garland <jeff_at_[hidden]>
>>
>> Yes, sorry I was off the net on holiday for an extended 
>> period :-)  Finally getting caught up now...
>>
> 
> Thanks!
> 
>> I would recommend that this be created as an alternative 
>> tz_database class -- 
>> something like 'historic timezone database'.  My experience 
>> is that must 
>> applications don't need the historic data and hence only 
>> really care about 
>> loading up the current set of rules.
> 
> I'm sure that's true for many users. But I also wonder how many users there
> are who do care but haven't had a problem until now because they're in
> countries where the rules haven't changed in recent years, so it's just
> worked.

Good point -- the US change is certainly an unusual event -- hopefully others 
will chime in on this.

> But let me put it the other way round. If a historical database were
> available, why would anyone choose to still use the existing method?

Memory usage would, I think, be the primary issue.

> Assuming the new method didn't impose a noticeable speed or memory
> constraint, of course.

I don't see how this is possible.  If you offer the full history of all 
timezones available for all historic time that would be a dramatic expansion 
of the size of the internal database.  At least this would be true without 
some significant redesign of the time zone class so that each instance of a 
particular region might share the tz rules with other instances -- currently 
each instance has a copy so adding the historical perspective would add alot 
of additional information for each region.

Jeff