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Author:halw

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Date:2008-11-03T01:48:11.000000Z


git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@103 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
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halw
2008-11-03 01:48:11 +00:00
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documentation/current/solutions/dates-and-times/eiffeltime/eiffeltime-tutorial/duration.wiki
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@@ -39,19 +39,19 @@ Two features ensure a link with the notion of ''day''. The first, <eiffel>to_day
For example, the current duration is 25:70:600. <eiffel>to_days</eiffel> will return 1 (one day) and <eiffel>time_modulo_day</eiffel> will return 2:20:0:. If the current duration is negative: -23:-80:300, <eiffel>to_days</eiffel> will return -2 (minus two days) and <eiffel>time_modulo_day</eiffel> will return 23:45:0.
Durations may be canonical or not canonical (tested using the <eiffel>BOOLEAN</eiffel> query <eiffel>canonical</eiffel>). That means the features <eiffel>hour</eiffel>, <eiffel>minute</eiffel>, and <eiffel>second</eiffel> are included in a particular range, or not. An instance of <eiffel>TIME_DURATION</eiffel> is canonical if:
Durations may be canonical or not canonical. This can be tested using the <eiffel>BOOLEAN</eiffel> query <eiffel>canonical</eiffel>. Canonical form depends upon whether the features <eiffel>hour</eiffel>, <eiffel>minute</eiffel>, and <eiffel>second</eiffel> have values that fall in a particular range. An instance of <eiffel>TIME_DURATION</eiffel> is canonical if:
* in the case of a positive duration (> zero), all of the three features have to be positive or 0, <eiffel>minute</eiffel> and <eiffel>second</eiffel> less than 60.
* in the case of a negative duration (< zero), all of the three features have to be negative or 0, <eiffel>minute</eiffel> and <eiffel>second</eiffel> strictly greater than -60. The function <eiffel>canonical</eiffel> tests if the duration is canonical or not, the function <eiffel>to_canonical</eiffel> yields a new duration equivalent to the current one and canonical.
* in the case of a negative duration (< zero), all of the three features have to be negative or 0, <eiffel>minute</eiffel> and <eiffel>second</eiffel> strictly greater than -60. The query <eiffel>canonical</eiffel> tests whether a duration is canonical. The query <eiffel>to_canonical</eiffel> yields a new, canonical <eiffel>TIME_DURATION</eiffel> equivalent to the query's target.
==DATE_DURATION==
Dealing with the Gregorian calendar is not so easy because of irregularities. A date duration of one month may be equal to 28 up to 31 days, depending on the current date! On the other hand, it could be useful to deal with precise duration. This issue leads to a unique point of design in the class: A separation is made between two kinds of instances: ''definite'' date durations and the ''relative'' date durations. The <eiffel>BOOLEAN</eiffel> query <eiffel>definite</eiffel> is true for definite durations and false otherwise.
<eiffel>DATE_DURATION</eiffel> is similar to <eiffel>TIME_DURATION</eiffel>, but models durations in dates rather than times. Dealing with the Gregorian calendar is not so easy because of its irregularities. A date duration of one month may be equal to 28, 29, 30, 31 days, depending on the current date! Sometimes though, it could be useful to deal with a precise date duration, just a number of days, independent of the current date. This issue leads to a unique point of design in the <eiffel>DATE_DURATION</eiffel> class: a separation is made between two kinds of instances: ''definite'' date durations and the ''relative'' date durations. The <eiffel>BOOLEAN</eiffel> query <eiffel>definite</eiffel> is <eiffel>True</eiffel> for definite date durations and false for relative date durations.
An instance is ''definite'' if and only if its attributes <eiffel>month</eiffel> and <eiffel>year</eiffel> are 0. Then only the number of days is used.
''Relative'' (non-definite) durations allow their attributes <eiffel>year</eiffel>, <eiffel>month</eiffel>, and <eiffel>day</eiffel> to have meaningful values, but disallow comparisons with other durations, for reasons that will be explained below.
The distinction between definite and relative date duration makes a difference when a duration is added to a date. In the case of a definite duration, there is no ambiguity: a given number of days is added to the date. In the case of a relative date duration, the result is relative to the origin date. For example, a one month duration may be equal to 28 days if the date is in February or 31 days if the date is in August. A duration becomes definite when its attributes <eiffel>year</eiffel> and <eiffel>month</eiffel> become 0. However it is possible to deal with instances of <eiffel>DATE_DURATION</eiffel> without taking care of this distinction.
The distinction between definite and relative date duration makes a difference when a duration is added to a date. In the case of a definite <eiffel>DATE_DURATION</eiffel>, there is no ambiguity: a given number of days is added to the date. In the case of a relative <eiffel>DATE_DURATION</eiffel>, the result is relative to the duration's <eiffel>origin_date</eiffel>. For example, a one month duration may be equal to 28 days if the date is in February or 31 days if the date is in August. A duration becomes definite when its attributes <eiffel>year</eiffel> and <eiffel>month</eiffel> become 0. However it is possible to deal with instances of <eiffel>DATE_DURATION</eiffel> without taking care of this distinction.
===Relative DATE_DURATION===
@@ -67,7 +67,7 @@ A way to compare two relative durations is to make them canonical from the same
===Definite DATE_DURATION===
Definite durations are characterized by the attribute day. Whenever a duration has its attributes year and month equal to 0, this duration is then definite. On the other hand, if one of these two attributes is not 0, the duration is not definite anymore.
Definite durations are characterized by the attribute <eiffel>day</eiffel>. Whenever a duration has its attributes <eiffel>year</eiffel> and <eiffel>month</eiffel> equal to 0, this duration is then definite. On the other hand, if one of these two attributes is not 0, the duration is relative.
The number of days between an origin date and the result of (date + duration) does not depend on the origin date. It is possible to compare definite date_duration to each other.The order is the one of day.