Re: [gobo-eiffel-develop] Questions regarding DT_TIME

[Eric B. <er...@go...>]

Paul Cohen wrote:
> I have implemented a very simple DT_STOPWATCH class for doing simple
> timing stuff (ie. start, stop & elapsed_time). In that class I use the
> feature DT_TIME.duration. To my surprise I occasionally get negative
> seconds and milliseconds.
> 
> In DT_TIME there is the feature:
> 
>     duration (other: like Current): DT_TIME_DURATION is
>             -- Duration between `other' and `Current'
>         do
>             Result := time_duration (other)
>         end
> 
> I then realize that DT_TIME.duration uses DT_TIME.time_duration which does:
> 
>     create Result.make_precise (hour - other.hour, minute -
> other.minute, second - other.second, millisecond - other.millisecond)
> 
> where Result & other are DT_TIME. I now realize that I must use
> DT_TIME.canonical_duration to get the result I expect since it
> calculates the difference (correctly) based on the milliseconds count
> of both DT_TIME instances.

All that is explained in $GOBO/doc/time/absolute.html#time

> My questions are:
> 
>    1. Why doesn't DT_TIME.duration use DT_TIME.canonical_duration?

DT_TIME.duration is just a quick way to compute the duration.
The result is correct. It's just that it is not canonical.
As you figured out, to get canonical result you can use
DT_TIME.canonical_duration, or call `set_canonical' on the
result of DT_TIME.duration.

>    2. When & why does anyone want to use DT_TIME.time_duration in its
> current implementation?

A program might want to compute several durations, add them together
and then compute the canonical form of the result instead of computing
the canonical form at each stage.

>    3. DT_TIME.time_duration has a misleading name. Better is
> DT_TIME.time_unit_differences or something like that which says what
> it does.

In fact `time_duration' is not meant to be used in DT_TIME.
You should use DT_TIME.duration instead. The usefulness of
`time_duration' comes in the descendant class DT_DATE_TIME.
It means the time part of the duration. In the same way
`date_duration' is the date part of the duration.

>    4. Is the Gobo project interested in my DT_STOPWATCH class?

Yes. But I'm just wondering why you use DT_TIME and not
DT_DATE_TIME. Don't you have problems when running it
around midnight?

-- 
Eric Bezault
mailto:er...@go...
http://www.gobosoft.com