| Limitations | |
The Gregorian calendar has been adopted in most western countries since the 16th century (e.g. since 20 December 1582 in France) with possible disruptions (e.g. French Revolutionary calendar used from 24 November 1793 to 31 December 1805). The Gobo Eiffel Time Library does not take this into account and considers that the Gregorian calendar was always in use (even at the time of dinosaurs) and will always be in the future.
The International Earth Rotation Service periodically uses leap seconds to keep UTC to within 0.9 second of UT1 (which measures the true angular orientation of the earth in space). There were no leap seconds before 1972 because the official mechanism accounting for the discrepancy between atomic time and the earth's rotation did not exist until the early 1970s. The Gobo Eiffel Time Library does not support leap seconds.
The maximum precision of the current implementation of DT_TIME is the millisecond. Although the public interface of DT_TIME has four fields (hour, minute, second and millisecond), its internal state is compacted into a single integer. Therefore in order for DT_TIME to work, your Eiffel compiler should implement INTEGER with at least 32 bits so that it can hold the number of milliseconds in one day (i.e. 86,400,000).
Some clients, such as classes which need to store and retrieve time objects efficiently, may want to have access to the compaction integer called storage. They can do so by simply inheriting from DT_TIME_HANDLER. The creation procedure make_from_storage is also available to descendants of DT_TIME_HANDLER.
Although the public interface of DT_DATE has three fields (year, month and day), its internal state is compacted into a single integer. Therefore in order for DT_DATE to work, your Eiffel compiler should implement INTEGER with at least 32 bits so that it can hold nowadays dates. The first five right-most bits are used to store the day, the next four bits to store the month. Considering that your Eiffel compiler implements INTEGER with 32 bits, this means that there are 23 bits left for the year. In such case the minimum date supported would be 1 January -4,194,305, and the maximum date would be 31 December 4,194,304.
Some clients, such as classes which need to store and retrieve date objects efficiently, may want to have access to the compaction integer called storage. They can do so by simply inheriting from DT_DATE_HANDLER. The creation procedure make_from_storage is also available to descendants of DT_DATE_HANDLER.
DT_DATE_TIME has of course the same implementation constraints as DT_DATE and DT_TIME. A date/time object has in fact two compaction integers, date_storage and time_storage, and clients should inherit from DT_DATE_TIME_HANDLER in order to have access to them.
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Copyright © 2000, Eric
Bezault mailto:ericb@gobosoft.com http://www.gobosoft.com Last Updated: 18 June 2000 |
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