Re: Ada, calendar, and daylight savings

[Corey Minyard <minyard@acm.org>]

Larry Kilgallen wrote:

> In article <3BDCEEFF.10409@acm.org>, Corey Minyard <minyard@acm.org> writes:
> 
>>I won't argue about the goofiness of our time system, since I can't do 
>>anything about that :-).
>>
>>Hopefully, missiles in flight are using UTC.  It makes no sense to use 
>>anything else.  However, you have no portable way of finding UTC in Ada. 
>>
> 
> Just ask for the time to be returned.
> 
> If your computer happens to be set to some unreliable source,
> such as my watch, then you are at _least_ 5 minutes off from
> _anybody's_ notion of time.  That is no longer a programming problem.
> 

You are correct, this is a system-level problem, not a programming 
language problem.  But it's relatively easy to solve to a pretty 
accurate level.

 >
 > Please don't burden Ada.Calendar with illogical constructs.

I don't agree with this.  Suppose I can build a system that has time 
reasonably coordinated between various parts of the system. 
"Reasonable" means "It's good enough for the application". It's not 
unreasonable to do this, I have done it many times, and I still can't 
use standard Ada to take advantage of this.  I could give thousands of 
examples, but I'll just give one.

I used to work on telephony systems, and for billing purposes, you 
should report UTC time, or some standard time, because the subscriber 
may not even be in the same timezone as the switch, and switches are
generally in different timezones and need to have their records 
coordinated.  Yet you generally want to report logs in local time and 
UTC time so the operators in the office can make sense of the logs and
machines can coordinate logs easily.  How are you going to do this in 
Ada?  You can't without using non-standard constructs.

Ok, I'll give another.  In the previous missile example, suppose the 
missile is communicating with satellites to maintain it's position.  It 
better be able to tell what time the satellites and ground stations are 
using and coordinate this with its time.  In distributed real-time 
systems, it's generally important to have some level of time 
coordination between system elements.

-Corey