1Date::Calc::Object(3) User Contributed Perl DocumentationDate::Calc::Object(3)
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3
4

NAME

6       Date::Calc::Object - Object-oriented add-on for Date::Calc with
7       overloaded operators
8

MOTTO

10       Make frequent things easy and infrequent or hard things possible
11

PREFACE

13       Note that you do NOT need to ""use Date::Calc qw(...);"" in addition to
14       this module.
15
16       Simply
17
18         use Date::Calc::Object qw(...);
19
20       INSTEAD OF
21
22         use Date::Calc qw(...);
23
24       with the same ""qw(...)"" as you would with the "Date::Calc" module,
25       and then forget about "Date::Calc::Object" altogether.
26
27       The rest of your existing code doesn't change at all.
28
29       Note also that in order to create a new date object, you do not need to
30       use
31
32         $date_object = Date::Calc::Object->new(...);
33
34       (but you may), and should use
35
36         $date_object = Date::Calc->new(...);
37
38       instead (saves you some typing and is a trifle faster).
39

SYNOPSIS

41   Export tags
42         :all  -  all functions from Date::Calc
43         :aux  -  auxiliary functions shift_*
44         :ALL  -  both :all and :aux
45
46   Functions
47       See Date::Calc(3) for a list of available functions.
48
49         $year                          = shift_year(\@_);
50         ($year,$mm,$dd)                = shift_date(\@_);
51         ($hrs,$min,$sec)               = shift_time(\@_);
52         ($year,$mm,$dd,$hrs,$min,$sec) = shift_datetime(\@_);
53
54   Methods
55         $old = Date::Calc->accurate_mode([FLAG]);
56         $old = Date::Calc->normalized_mode([FLAG]);
57         $old = Date::Calc->number_format([NUMBER|CODEREF]);
58         $old = Date::Calc->delta_format([NUMBER|CODEREF]);  # global default
59         $old = Date::Calc->date_format([NUMBER|CODEREF]);   # global default
60         $old = Date::Calc->language([LANGUAGE]);            # global default - DEPRECATED
61
62         $old = $date->accurate_mode([FLAG]);           # is global nevertheless!
63         $old = $date->normalized_mode([FLAG]);         # is global nevertheless!
64         $old = $date->number_format([NUMBER|CODEREF]); # is global nevertheless!
65         $old = $date->delta_format([NUMBER|CODEREF]);  # individual override
66         $old = $date->date_format([NUMBER|CODEREF]);   # individual override
67         $old = $date->language([LANGUAGE]);            # individual override
68
69         $flag = $date->is_delta();
70         $flag = $date->is_date();
71         $flag = $date->is_short(); # i.e., has no time part
72         $flag = $date->is_long();  # i.e., has time part
73         $flag = $date->is_valid();
74
75         $date = Date::Calc->new([TYPE]);
76         $date = Date::Calc->new([TYPE,]YEAR,MONTH,DAY[,HRS,MIN,SEC]);
77         $date = Date::Calc->new($arrayref);
78         $newdate = $somedate->new([TYPE]);
79         $newdate = $somedate->new([TYPE,]YEAR,MONTH,DAY[,HRS,MIN,SEC]);
80         $newdate = $somedate->new($arrayref);
81
82         $datecopy = $date->clone();
83         $targetdate->copy($sourcedate);
84         $targetdate->copy($arrayref);
85         $targetdate->copy(@list);
86
87         ($year,$month,$day) = $date->date([TYPE]);
88         ($year,$month,$day) = $date->date([TYPE,]YEAR,MONTH,DAY[,HRS,MIN,SEC]);
89         ($year,$month,$day) = $date->date($arrayref);
90         ([$hrs,$min,$sec])  = $date->time([TYPE]);
91         ($hrs,$min,$sec)    = $date->time([TYPE,]HRS,MIN,SEC);
92         ([$hrs,$min,$sec])  = $date->time($arrayref);
93
94         ($year,$month,$day,$hrs,$min,$sec) =
95             $date->datetime([TYPE]);
96         ($year,$month,$day,$hrs,$min,$sec) =
97             $date->datetime([TYPE,]YEAR,MONTH,DAY[,HRS,MIN,SEC]);
98
99         $date  = Date::Calc->today([FLAG]);
100         $date  = Date::Calc->now([FLAG]); # shorthand for --+
101         $date  = Date::Calc->today_and_now([FLAG]); # <-----+
102         $date  = Date::Calc->gmtime([time]);    # UTC/GMT
103         $date  = Date::Calc->localtime([time]); # local time
104         $delta = Date::Calc->tzoffset([time]);
105         $date  = Date::Calc->time2date([time]); # UTC/GMT
106
107         $date->today([FLAG]);         # updates the date part only
108         $date->now([FLAG]);           # updates the time part only
109         $date->today_and_now([FLAG]); # updates both date and time
110         $date->gmtime([time]);        # updates both date and time (UTC/GMT)
111         $date->localtime([time]);     # updates both date and time (local time)
112         $delta->tzoffset([time]);     # updates both date and time
113         $date->time2date([time]);     # updates both date and time (UTC/GMT)
114
115         $time = Date::Calc->mktime();    # same as "$time = CORE::time();"
116         $time = Date::Calc->date2time(); # same as "$time = CORE::time();"
117
118         $time = $date->mktime();      # converts into Unix time (local time)
119         $time = $date->date2time();   # converts into Unix time (UTC/GMT)
120
121         $year    = $date->year([YEAR]);
122         $month   = $date->month([MONTH]);
123         $day     = $date->day([DAY]);
124         $hours   = $date->hours([HRS]);
125         $minutes = $date->minutes([MIN]);
126         $seconds = $date->seconds([SEC]);
127
128         $number = $date->number([NUMBER|CODEREF]);
129         $string = $date->string([NUMBER|CODEREF][,LANGUAGE]);
130
131         $delta->normalize(); # renormalizes a delta vector
132
133   Overloaded Operators
134         #####################################################
135         # Scalar operands are always converted into a delta #
136         # vector with that many days, i.e., [1,0,0,SCALAR]  #
137         #####################################################
138
139   Comparison Operators:
140         if ($date1 <  $date2) { # compares date part only
141         if ($date1 <= $date2) { # compares date part only
142         if ($date1 >  $date2) { # compares date part only
143         if ($date1 >= $date2) { # compares date part only
144         if ($date1 == $date2) { # compares date part only
145         if ($date1 != $date2) { # compares date part only
146
147         $comp = $date1 <=> $date2; # compares date part only
148
149         if ($date1 lt $date2) { # compares both date and time
150         if ($date1 le $date2) { # compares both date and time
151         if ($date1 gt $date2) { # compares both date and time
152         if ($date1 ge $date2) { # compares both date and time
153         if ($date1 eq $date2) { # compares both date and time
154         if ($date1 ne $date2) { # compares both date and time
155
156         $comp = $date1 cmp $date2; # compares both date and time
157
158       Note that you can of course also compare two deltas, but not a date and
159       a delta!
160
161         ##################################################
162         # Default TYPE for array refs in comparisons is: #
163         # Same as other operand                          #
164         ##################################################
165
166         if ([2000,4,1] == $date) {
167         if ($today > [2000,4,1]) {
168
169         if ($now ge [2000,3,26,2,0,0]) {
170
171         if ($delta == [18,0,0]) {
172         if ($delta == -1) {
173
174   Plus:
175         $date2 = $date1 + $delta;
176         $date2 = $delta + $date1;
177         $date += $delta;
178         $this = $date++;
179         $next = ++$date;
180
181         $delta3 = $delta1 + $delta2;
182         $delta1 += $delta2;
183         $delta += $date; # beware of implicit type change!
184         $delta++;
185         ++$delta;
186
187         #####################################################
188         # Default TYPE for array refs in '+' operations is: #
189         # Opposite of other operand                         #
190         #####################################################
191
192         $date2 = [2000,3,26] + $delta;
193         $date2 = $date1 + [+1,0,0];
194         $date2 = [0,0,-1] + $date1;
195         $date2 = $date1 + 1;
196         $date += [0,0,+1];
197         $date += 2;
198
199         $delta3 = [1,+1,0,-1] + $delta2;
200         $delta3 = $delta1 + [1,0,0,+1];
201         $delta3 = $delta1 + 1;
202         $delta += [1,0,+1,0];
203         $delta += [2000,3,26]; # beware of implicit type change!
204         $delta += 7;
205
206   Unary Minus:
207         $delta2 = -$delta1;
208
209   Minus:
210         $delta = $date2 - $date1;
211         $date2 = $date1 - $delta;
212         $date -= $delta;
213         $date2 -= $date1; # beware of implicit type change!
214         $this = $date--;
215         $prev = --$date;
216
217         $delta3 = $delta2 - $delta1;
218         $delta2 -= $delta1;
219         $delta--;
220         --$delta;
221
222         #####################################################
223         # Default TYPE for array refs in '-' operations is: #
224         # Always a date                                     #
225         #####################################################
226
227         $delta = $today - [2000,3,26];
228         $delta = [2000,4,1] - $date;
229         $date2 = [2000,3,26] - $delta;
230         $date2 = $date1 - [1,0,0,+7];
231         $date2 = $date1 - 7;
232         $date -= [1,0,0,+1]; # better add [0,0,-1] instead!
233         $date2 -= [2000,3,26]; # beware of implicit type change!
234         $date2 -= 1;
235
236         $delta3 = [1,0,+1,0] - $delta1;
237         $delta3 = $delta2 - [1,0,0,-1];
238         $delta -= [1,0,0,+1];
239         $delta -= 7;
240
241   Miscellaneous Operators:
242         $string = "$date";
243         $string = "$delta";
244
245         print "$date\n";
246         print "$delta\n";
247
248         if ($date) { # date is valid
249         if ($delta) { # delta is valid
250
251         $days = abs($date);
252         $diff = abs($delta); # can be negative!
253
254         $diff = abs(abs($delta)); # always positive
255

DESCRIPTION

257       • FLAG
258
259         "FLAG" is either 0 (for "false") or 1 (for "true").
260
261         In the case of ""accurate_mode()"" and ""normalized_mode()"", this
262         switches the corresponding mode on and off (see further below for an
263         explanation of what these are).
264
265         In the case of ""today()"", ""now()"" and ""today_and_now()"", a
266         "true" value indicates "GMT" (Greenwich Mean Time), as opposed to
267         local time, which is the default.
268
269       • NUMBER
270
271         "NUMBER" is a number between 0 and 2 (for "number_format()" and
272         "number()") or between 0 and 4 (for "delta_format()", "date_format()"
273         and "string()"), indicating which of the three/five predefined
274         formats, respectively, should be used for converting a date into
275         numeric representation (needed for comparing dates, for instance) or
276         string representation.
277
278         Format #0 is the default at startup and the simplest of all (and
279         should be fastest to calculate, too).
280
281         The string representation of dates in format #0 also has the
282         advantage of being sortable in chronological order (and of complying
283         with ISO 8601).
284
285         (The numeric formats are (trivially) always sortable in chronological
286         order of course.)
287
288         The other formats are (mostly) increasingly more sophisticated (in
289         terms of esthetics and computation time) with increasing number
290         (except for format #4):
291
292           Delta number formats (short):
293
294               0    13603
295               1    13603
296               2    13603
297
298           Delta string formats (short):
299
300               0    '+0+0+13603'
301               1    '+0 +0 +13603'
302               2    '+0Y +0M +13603D'
303               3    '+0 Y +0 M +13603 D'
304               4    '(0,0,13603)'
305
306           Date number formats (short):
307
308               0    20010401
309               1    730576
310               2    730576
311
312           Date string formats (short):
313
314               0    '20010401'
315               1    '01-Apr-2001'
316               2    'Sun 1-Apr-2001'
317               3    'Sunday, April 1st 2001'
318               4    '[2001,4,1]'
319
320           Delta number formats (long):
321
322               0    13603.012959
323               1    13603.012959
324               2    13603.0624884259
325
326           Delta string formats (long):
327
328               0    '+0+0+13603+1+29+59'
329               1    '+0 +0 +13603 +1 +29 +59'
330               2    '+0Y +0M +13603D +1h +29m +59s'
331               3    '+0 Y +0 M +13603 D +1 h +29 m +59 s'
332               4    '(0,0,13603,1,29,59)'
333
334           Date number formats (long):
335
336               0    20010401.082959
337               1    730576.082959
338               2    730576.354155093
339
340           Date string formats (long):
341
342               0    '20010401082959'
343               1    '01-Apr-2001 08:29:59'
344               2    'Sun 1-Apr-2001 08:29:59'
345               3    'Sunday, April 1st 2001 08:29:59'
346               4    '[2001,4,1,8,29,59]'
347
348         If a number outside of the permitted range is specified, or if the
349         value is not a code reference (see also the next section below for
350         more details), the default format #0 is used instead.
351
352       • CODEREF
353
354         "CODEREF" is the reference of a subroutine which can be passed to the
355         methods "number_format()", "delta_format()" and "date_format()" in
356         order to install a callback function which will be called
357         subsequently whenever a date (or delta) object needs to be
358         (implicitly) converted into a number or string.
359
360         This happens for instance when you compare two date objects, or when
361         you put a date object reference in a string between double quotes.
362
363         Such a "CODEREF" can also be passed to the methods "number()" and
364         "string()" for explicitly converting a date object as desired.
365
366       • LANGUAGE
367
368         "LANGUAGE" is either a number in the range "[1..Languages()]", or one
369         of the strings ""Language_to_Text(1..Languages())"" (see also
370         Date::Calc(3)).
371
372       • TYPE
373
374         "TYPE" is 0 for a regular date and 1 for a delta vector (a list of
375         year, month, day and optionally hours, minutes and seconds offsets).
376
377       • Storage
378
379         "Date::Calc" objects are implemented as two nested arrays.
380
381         The "blessed" array (whose reference is the object reference you
382         receive when calling the "new()" method) contains an anonymous array
383         at position zero and the object's data in its remaining fields.
384
385         The embedded anonymous array is used for storing the object's
386         attributes (flags).
387
388         Dates and delta vectors always comprise either 3 or 6 data values:
389         Year, month, day plus (optionally) hours, minutes and seconds.
390
391         These values are stored in the "blessed" array at positions 1..3 or
392         1..6, respectively.
393
394         An object without the time values is therefore called "short", and an
395         object having time values is called "long" throughout this manual.
396
397         Hint: Whenever possible, if you do not need the time values, omit
398         them, i.e., always use the "short" form of the object if possible,
399         this will speed up calculations a little (the short form uses
400         different (faster) functions for all calculations internally).
401
402         The embedded anonymous array contains various flags:
403
404         At position zero, it contains the "TYPE" indicator which determines
405         whether the object is a date or a delta vector.
406
407         At position 1, the object stores the "NUMBER" of one of the delta
408         vector formats, or the reference of a callback function which
409         converts the contents of the object into string representation if
410         it's a delta vector, or "undef" if the global settings apply.
411
412         At position 2, the object stores the "NUMBER" of one of the date
413         formats, or the reference of a callback function which converts the
414         contents of the object into string representation if it's a date, or
415         "undef" if the global settings apply.
416
417         At position 3, the object stores the "LANGUAGE" to be used for all
418         conversions into strings (where applicable), or "undef" if the global
419         language setting applies.
420
421         Note that your callback functions (see the section "Callback
422         Functions" further below for more details) should not pay attention
423         to this value at position 3, because they get a parameter which tells
424         them which language to use (this is necessary in order to allow
425         temporary overrides).
426
427         If your callback handlers use the "*_to_Text*" functions (or any
428         other language-dependent function) from the "Date::Calc" module, your
429         handlers should pass on this language parameter to these functions
430         (and not the value from position 3).
431
432         Be reminded though that you should NEVER access the object's internal
433         data directly, i.e., through their positional numbers, but ALWAYS
434         through their respective accessor methods, e.g.:
435
436                 year()
437                 month()
438                 day()
439                 hours()
440                 minutes()
441                 seconds()
442                 date()
443                 time()
444                 datetime()
445                 is_delta()
446                 is_date()
447                 is_short()
448                 is_long()
449                 delta_format()
450                 date_format()
451                 language()
452
453         And although position 4 and onward in the embedded anonymous array is
454         currently unused, it might not stay so in future releases of this
455         module.
456
457         Therefore, in case you need more attributes in a subclass of the
458         "Date::Calc[::Object]" class, I suggest using values starting at
459         positions a bit further up, e.g. 6, 8 or 10.
460
461       • Invalid Dates
462
463         Only "new()" allows to create objects containing possibly invalid
464         dates (needed for reading in and evaluating user input, for example).
465
466       • Usage
467
468         The methods
469
470                 accurate_mode()
471                 normalized_mode()
472                 number_format()
473                 delta_format()
474                 date_format()
475                 language()
476                 date()
477                 time()
478                 datetime()
479                 year()
480                 month()
481                 day()
482                 hours()
483                 minutes()
484                 seconds()
485
486         are used for reading as well as for setting attributes. They simply
487         return the values in question if they are called without parameters.
488
489         The methods
490
491                 accurate_mode()
492                 normalized_mode()
493                 number_format()
494                 delta_format()
495                 date_format()
496                 language()
497
498         always return the previous value if a new value is set. This allows
499         you to change these values temporarily and to restore their old value
500         afterwards more easily (but you can also override the "format" and
501         "language" settings directly when calling the "number()" or
502         "string()" method).
503
504         The methods
505
506                 date()
507                 time()
508                 datetime()
509                 year()
510                 month()
511                 day()
512                 hours()
513                 minutes()
514                 seconds()
515
516         always return the new values when the corresponding values have been
517         changed.
518
519         The method "date()" NEVER returns the time values (hours, minutes,
520         seconds) even if they have just been set using this method (which the
521         method optionally allows). Otherwise it would be very hard to predict
522         the exact number of values it returns, which might lead to errors
523         (wrong number of parameters) elsewhere in your program.
524
525         The method "datetime()" ALWAYS returns the time values (hours,
526         minutes, seconds) even if the object in question lacks a time part.
527         In that case, zeros are returned for hours, minutes and seconds
528         instead (but the stored time part is left unchanged, whether it
529         exists or not).
530
531         If you do not provide values for hours, minutes and seconds when
532         using the method "date()" to set the values for year, month and day,
533         the time part will not be changed (whether it exists or not).
534
535         If you do not provide values for hours, minutes and seconds when
536         using the method "datetime()" to set the values for year, month and
537         day, the time part will be filled with zeros (the time part will be
538         created if necessary).
539
540         If the object is short, i.e., if it does not have any time values,
541         the method "time()" returns an empty list.
542
543         If the object is short and the methods "hours()", "minutes()" or
544         "seconds()" are used to set any of these time values, the object is
545         automatically promoted to the "long" form, and the other two time
546         values are filled with zeros.
547
548         The following methods can also return "undef" under certain
549         circumstances:
550
551                 delta_format()
552                 date_format()
553                 language()
554                 is_delta()
555                 is_date()
556                 is_short()
557                 is_long()
558                 is_valid()
559                 hours()
560                 minutes()
561                 seconds()
562                 number()
563                 string()
564
565         The methods "delta_format()", "date_format()" and "language()" return
566         "undef" when they are called as object methods and no individual
567         override has been defined for the object in question.
568
569         The "is_*()" predicate methods return "undef" if the object in
570         question does not have the expected internal structure. This can
571         happen for instance when you create an empty object with "new()".
572
573         When called without parameters, the methods "hours()", "minutes()"
574         and "seconds()" return "undef" if the object in question does not
575         have a time part.
576
577         The methods "number()" and "string()" return "undef" if the object in
578         question is not valid (i.e., if "is_valid()" returns "undef" or
579         false).
580
581         And finally, the methods
582
583                 copy()
584                 today()
585                 now()
586                 today_and_now()
587                 gmtime()
588                 localtime()
589                 tzoffset()
590                 time2date()
591                 normalize()
592
593         return the object reference of the (target) object in question for
594         convenience.
595
596       • Import/Export
597
598         Note that you can import and export Unix "time" values using the
599         methods "gmtime()", "localtime()", "mktime()", "date2time()" and
600         "time2date()", both as local time or as UTC/GMT.
601
602       • Accurate Mode and Normalized Mode
603
604         The method "accurate_mode()" controls the internal flag which
605         determines which of two fundamental modes of operation is used.
606
607         When set to true (the default at startup), delta vectors are
608         calculated to give the exact difference in days between two dates.
609         The "year" and "month" entries in the resulting delta vector are
610         always zero in that case.
611
612         If "accurate mode" is switched off (when the corresponding flag is
613         set to false), delta vectors are calculated with year and month
614         differences.
615
616         E.g., the difference between "[1999,12,6]" and "[2000,6,24]" is "[+0
617         +0 +201]" (plus 201 days) in accurate mode and "[+1 -6 +18]" (plus
618         one year, minus 6 months, plus 18 days) when accurate mode is
619         switched off, and is "[+0 +6 +18]" (plus 6 months, plus 18 days) if
620         additionally, "normalized mode" is switched on.
621
622         The delta vector is calculated by simply taking the difference in
623         years, the difference in months and the difference in days (if
624         "accurate mode" is switched off and if "normalized mode" has not been
625         switched on). This is called "one-by-one" semantics or "year-month-
626         day mode"; "YMD mode" for short.
627
628         When "normalized mode" is switched on (while "accurate mode" is
629         switched off), the delta vector is calculated in a more complex way
630         involving the functions ""Add_Delta_YM()"" (for "truncation") and
631         ""Delta_Days()"".
632
633         Moreover, the result is normalized, i.e., the return values are
634         guaranteed to all have the same sign (or to be zero), and to all be
635         "minimal", i.e., not to exceed the ranges "[-11..+11]" for months,
636         "[-30..+30]" for days, "[-23..+23]" for hours and "[-59..+59]" for
637         minutes and seconds.
638
639         The rule is to add these result values to a date in a left-to-right
640         order, and to truncate invalid intermediate dates, such as e.g.
641         "[2009,2,29]", to the last valid day of that same month, e.g.
642         "[2009,2,28]". This is called "left-to-right with truncation"
643         semantics or "normalized mode"; "N_YMD mode" for short.
644
645         The method "normalized_mode()" controls the internal flag which
646         determines whether "YMD mode" is used (the default at startup, for
647         reasons of backward compatibility) or "N_YMD mode".
648
649         Note that also for reasons of backward compatibility, this flag only
650         has effect when "accurate mode" is switched off.
651
652         Both flags can be set and reset independently from each other,
653         however.
654
655         Therefore, at startup, you can for instance switch "normalized mode"
656         on, without having any immediate effect, and switch off "accurate
657         mode" later, which instantly also causes "normalized mode" to spring
658         into effect.
659
660         Because years and months have varying lengths in terms of days, the
661         "YMD" and "N_YMD" modes are less accurate than "accurate mode",
662         because these modes depend on the context of the two dates of which
663         the delta vector is the difference. Added to a different date, a
664         delta vector calculated in "YMD mode" or "N_YMD mode" may yield a
665         different offset in terms of days, i.e., the final result may
666         sometimes vary seemingly unpredictably (or in other situations may
667         give you the expected result, at the expense of actually representing
668         a varying difference in days, determined exclusively by context).
669
670         Beware also that - for the same reason - the absolute value
671         (""abs()"") of a delta vector returns a fictitious number of days if
672         the delta vector contains non-zero values for "year" and/or "month"
673         (see also the next section "Absolute Value" below for more details).
674
675         Example:
676
677         The difference between "[2000,1,1]" and "[2000,3,1]" is "[+0 +0 +60]"
678         in "accurate mode" and "[+0 +2 +0]" in "YMD mode" (in this "benign"
679         example, the result is the same in "YMD mode" and in "N_YMD mode").
680
681         When added to the date "[2000,4,1]", the "accurate" delta vector
682         yields the date "[2000,5,31]", whereas the "YMD mode" delta vector
683         yields the date "[2000,6,1]" (which is actually a difference of 61
684         days).
685
686         Moreover, when added to the date "[1999,1,1]", the "accurate" delta
687         vector yields the date "[1999,3,2]", whereas the "inaccurate" "YMD
688         Mode" delta vector yields the date "[1999,3,1]" (which is actually a
689         difference of 59 days).
690
691         Depending on what you want, either mode may suit you better.
692
693       • Absolute Value
694
695         Note that ""abs($date)"" and ""abs($delta)"" are just shorthands for
696         ""$date->number()"" and ""$delta->number()"".
697
698         The operator ""abs()"", when applied to a date or delta vector,
699         returns the corresponding number of days (see below for an exception
700         to this), with the time part (if available) represented by a fraction
701         after the decimal point.
702
703         In the case of dates, the absolute value (to the left of the decimal
704         point) is the number of days since the 1st of January 1 A.D. (by
705         extrapolating the Gregorian calendar back beyond its "natural" limit
706         of 1582 A.D.) PLUS ONE.
707
708         (I.e., the absolute value of the 1st of January 1 A.D. is 1.)
709
710         Exception:
711
712         If the "NUMBER" or "number_format()" is set to 0 (the default
713         setting), the absolute value of a date to the left of the decimal
714         point is "yyyymmdd", i.e., the number in which the uppermost four
715         digits correspond to the year, the next lower two digits to the month
716         and the lowermost two digits to the day.
717
718         In the case of delta vectors, the absolute value (to the left of the
719         decimal point) is simply the difference in days (but see also below).
720
721         Note that the absolute value of a delta vector can be negative!
722
723         If you want a positive value in all cases, apply the ""abs()""
724         operator again, i.e., ""$posdiff = abs(abs($delta));"".
725
726         If the delta vector contains non-zero values for "year" and/or
727         "month" (see also the discussion of "Accurate Mode" in the section
728         above), an exact representation in days cannot be calculated, because
729         years and months do not have fixed equivalents in days.
730
731         If nevertheless you attempt to calculate the absolute value of such a
732         delta vector, a fictitious value is returned, which is calculated by
733         simply multiplying the year difference with 12, adding the month
734         difference, multiplying this sum with 31 and finally adding the day
735         difference.
736
737         Beware that because of this, the absolute values of delta vectors are
738         not necessarily contiguous.
739
740         Moreover, since there is more than one way to express the difference
741         between two dates, comparisons of delta vectors may not always yield
742         the expected result.
743
744         Example:
745
746         The difference between the two dates "[2000,4,30]" and "[2001,5,1]"
747         can be expressed as "[+1 +1 -29]", or as "[+1 +0 +1]".
748
749         The first delta vector has an absolute value of 374, whereas the
750         latter delta vector has an absolute value of only 373 (while the true
751         difference in days between the two dates is 366).
752
753         If the date or delta vector has a time part, the time is returned as
754         a fraction of a full day after the decimal point as follows:
755
756         If the "NUMBER" or "number_format()" is set to 0 (the default
757         setting) or 1, this fraction is simply ".hhmmss", i.e., the two
758         digits after the decimal point represent the hours, the next two
759         digits the minutes and the last two digits the seconds.
760
761         Note that you cannot simply add and subtract these values to yield
762         meaningful dates or deltas again, you can only use them for
763         comparisons (equal, not equal, less than, greater than, etc.). If you
764         want to add/subtract, read on:
765
766         Only when the "NUMBER" or "number_format()" is set to 2, this
767         fraction will be the equivalent number of seconds (i.e., "(((hours *
768         60) + minutes) * 60) + seconds") divided by the number of seconds in
769         a full day (i.e., "24*60*60 = 86400"), or "0/86400", "1/86400", ... ,
770         "86399/86400".
771
772         In other words, the (mathematically correct) fraction of a day.
773
774         You can safely perform arithmetics with these values as far as the
775         internal precision of your vendor's implementation of the C run-time
776         library (on which Perl depends) will permit.
777
778       • Renormalizing Delta Vectors
779
780         When adding or subtracting delta vectors to/from one another, the
781         addition or subtraction takes place component by component.
782
783         Example:
784
785           [+0 +0 +0 +3 +29 +50] + [+0 +0 +0 +0 +55 +5] = [+0 +0 +0 +3 +84 +55]
786           [+0 +0 +0 +3 +29 +50] - [+0 +0 +0 +0 +55 +5] = [+0 +0 +0 +3 -26 +45]
787
788         This may result in time values outside the usual ranges ("[-23..+23]"
789         for hours and "[-59..+59]" for minutes and seconds).
790
791         Note that even though the delta value for days will often become
792         quite large, it is impossible to renormalize this value because there
793         is no constant conversion factor from days to months (should it be
794         28, 29, 30 or 31?).
795
796         If accurate mode (see further above for what that is) is switched
797         off, delta vectors can also contain non-zero values for years and
798         months. If you add or subtract these, the value for months can lie
799         outside the range "[-11..11]", which isn't wrong, but may seem funny.
800
801         Therefore, the "normalize()" method will also renormalize the
802         "months" value, if and only if accurate mode has been switched off.
803         (!)
804
805         (Hence, switch accurate mode ON temporarily if you DON'T want the
806         renormalization of the "months" value to happen.)
807
808         If you want to force the time values from the example above back into
809         their proper ranges, use the "normalize()" method as follows:
810
811           print "[$delta]\n";
812           $delta->normalize();
813           print "[$delta]\n";
814
815         This will print
816
817           [+0 +0 +0 +3 +84 +55]
818           [+0 +0 +0 +4 +24 +55]
819
820         for the first and
821
822           [+0 +0 +0 +3 -26 +45]
823           [+0 +0 +0 +2 +34 +45]
824
825         for the second delta vector from the example further above.
826
827         Note that the values for days, hours, minutes and seconds are
828         guaranteed to have the same sign after the renormalization.
829
830         Under "normal" circumstances, i.e., when accurate mode is on (the
831         default), this method only has an effect on the time part of the
832         delta vector.
833
834         If the delta vector in question does not have a time part, nothing
835         happens.
836
837         If accurate mode is off, the "months" value is also normalized, i.e.,
838         if it lies outside of the range "[-11..11]", integer multiples of 12
839         are added to the "years" value and subtracted from the "months"
840         value. Moreover, the "months" value is guaranteed to have the same
841         sign as the values for days, hours, minutes and seconds, unless the
842         "months" value is zero or the values for days, hours, minutes and
843         seconds are all zero.
844
845         If the object in question is a date and if warnings are enabled, the
846         message "normalizing a date is a no-op" will be printed to STDERR.
847
848         If the object in question is not a valid "Date::Calc" object, nothing
849         happens.
850
851         The method returns its object's reference, which allows chaining of
852         method calls, as in the following example:
853
854           @time = $delta->normalize()->time();
855
856       • Callback Functions
857
858         Note that you are not restricted to the built-in formats (numbered
859         from 0 to 2 for "number_format()" and "number()" and from 0 to 4 for
860         "delta_format()", "date_format()" and "string()") for converting a
861         date or delta object into a number or string.
862
863         You can also provide your own function(s) for doing so, in order to
864         suit your own taste or needs, by passing a subroutine reference to
865         the appropriate method, i.e., "number_format()", "number()",
866         "delta_format()", "date_format()" and "string()".
867
868         You can pass a handler to only one or more of these methods, or to
869         all of them, as you like. You can use different callback functions,
870         or the same for all.
871
872         In order to facilitate the latter, and in order to make the decoding
873         of the various cases easier for you, the callback function receives a
874         uniquely identifying function code as its second parameter:
875
876           0  =  TO_NUMBER | IS_DATE  | IS_SHORT  (number[_format])
877           1  =  TO_NUMBER | IS_DATE  | IS_LONG   (number[_format])
878           2  =  TO_NUMBER | IS_DELTA | IS_SHORT  (number[_format])
879           3  =  TO_NUMBER | IS_DELTA | IS_LONG   (number[_format])
880           4  =  TO_STRING | IS_DATE  | IS_SHORT  (string|date_format)
881           5  =  TO_STRING | IS_DATE  | IS_LONG   (string|date_format)
882           6  =  TO_STRING | IS_DELTA | IS_SHORT  (string|delta_format)
883           7  =  TO_STRING | IS_DELTA | IS_LONG   (string|delta_format)
884
885         The first parameter of the callback function is of course the
886         reference of the object in question itself (therefore, the callback
887         function can actually be an object method - but not a class method,
888         for obvious reasons).
889
890         The third parameter is the number of the language (in the range
891         "[1..Languages()]") which you should always pass along when using any
892         of the following functions from the "Date::Calc" module in your
893         handler:
894
895         "Decode_Month()", "Decode_Day_of_Week()", "Compressed_to_Text()",
896         "Date_to_Text()", "Date_to_Text_Long()", "Calendar()",
897         "Month_to_Text()", "Day_of_Week_to_Text()",
898         "Day_of_Week_Abbreviation()", "Decode_Date_EU()", "Decode_Date_US()",
899         "Decode_Date_EU2()", "Decode_Date_US2()", "Parse_Date()".
900
901         The callback handler should return the resulting number or string, as
902         requested.
903
904         BEWARE that you should NEVER rely upon any knowledge of the object's
905         internal structure, as this may be subject to change!
906
907         ALWAYS use the test and access methods provided by this module!
908
909         Example:
910
911           sub handler
912           {
913               my($self,$code,$lang) = @_;
914
915               if    ($code == 0) # TO_NUMBER | IS_DATE  | IS_SHORT
916               {
917                   return Date_to_Days( $self->date() );
918               }
919               elsif ($code == 1) # TO_NUMBER | IS_DATE  | IS_LONG
920               {
921                   return Date_to_Days( $self->date() ) +
922                                    ( ( $self->hours() * 60 +
923                                        $self->minutes() ) * 60 +
924                                        $self->seconds() ) / 86400;
925               }
926               elsif ($code == 2) # TO_NUMBER | IS_DELTA | IS_SHORT
927               {
928                   return ( $self->year() * 12 +
929                            $self->month() ) * 31 +
930                            $self->day();
931               }
932               elsif ($code == 3) # TO_NUMBER | IS_DELTA | IS_LONG
933               {
934                   return ( $self->year() * 12 +
935                            $self->month() ) * 31 +
936                            $self->day() +
937                        ( ( $self->hours() * 60 +
938                            $self->minutes() ) * 60 +
939                            $self->seconds() ) / 86400;
940               }
941               elsif ($code == 4) # TO_STRING | IS_DATE  | IS_SHORT
942               {
943                   return join( "/", $self->date() );
944               }
945               elsif ($code == 5) # TO_STRING | IS_DATE  | IS_LONG
946               {
947                   return join( "/", $self->date() ) . " " .
948                          join( ":", $self->time() );
949               }
950               elsif ($code == 6) # TO_STRING | IS_DELTA | IS_SHORT
951               {
952                   return join( "|", $self->date() );
953               }
954               elsif ($code == 7) # TO_STRING | IS_DELTA | IS_LONG
955               {
956                   return join( "|", $self->datetime() );
957               }
958               else
959               {
960                   die "internal error";
961               }
962           }
963
964           Date::Calc->number_format(\&handler);
965           Date::Calc->delta_format(\&handler);
966           Date::Calc->date_format(\&handler);
967
968         This sets our handler to take care of all automatic conversions, such
969         as needed when comparing dates or when interpolating a string in
970         double quotes which contains a date object.
971
972         To deactivate a handler, simply pass a valid format number to the
973         method in question, e.g.:
974
975           Date::Calc->number_format(0);
976           Date::Calc->delta_format(2);
977           Date::Calc->date_format(3);
978
979         When calling the "number()" or "string()" method explicitly, you can
980         pass a different format number (than the global setting), like this:
981
982           $number = $date->number(2);
983           $string = $date->string(1);
984
985         You can also pass a handler's reference, like so:
986
987           $number = $date->number(\&handler);
988           $string = $date->string(\&handler);
989
990         This overrides the global setting and the individual object's local
991         setting for the duration of the call of "number()" or "string()" (but
992         doesn't change the global or local settings themselves).
993
994         Moreover, you can also define individual overrides for the date and
995         the delta vector formats (but not the number format) for individual
996         objects, e.g.:
997
998           $date->delta_format(1);
999           $date->date_format(2);
1000
1001           $date->delta_format(\&handler);
1002           $date->date_format(\&handler);
1003
1004         In order to deactivate an individual handler for an object, and/or in
1005         order to deactivate any override altogether (so that the global
1006         settings apply again), you have to pass "undef" explicitly to the
1007         method in question:
1008
1009           $date->delta_format(undef);
1010           $date->date_format(undef);
1011
1012         You can also define a language for individual objects (see the next
1013         section immediately below for more details).
1014
1015         If such an individual language override has been set, it will be
1016         passed to your callback handlers as the third parameter (in the case
1017         of "string" conversions, but not in the case of "number"
1018         conversions).
1019
1020         Otherwise, the global settings as defined by "Language($lang);" or
1021         "Date::Calc-"language($lang);> will be passed to your handler.
1022
1023       • Languages
1024
1025         Note that this module is completely transparent to the setting of a
1026         language in "Date::Calc". This means that you can choose a language
1027         in "Date::Calc" (with the "Language()" function) and all dates
1028         subsequently printed by this module will automatically be in that
1029         language - provided that you use the built-in formats of this module,
1030         or that you pass the third parameter of the callback funtion to the
1031         funtions of the "Date::Calc" module which accept it.
1032
1033         However, this global language setting can be overridden for
1034         individual date (or delta) objects by using the OBJECT method
1035
1036             $oldlang = $date->language($newlang);
1037
1038         (The global setting is not altered by this in any way.)
1039
1040         In order to deactivate such an individual language setting (so that
1041         the global setting applies again), simply pass the value "undef"
1042         explicitly to the "language()" object method:
1043
1044           $date->language(undef);
1045
1046         The CLASS method
1047
1048             $oldlang = Date::Calc->language($newlang);
1049
1050         is just a convenient wrapper around the "Language()" function, which
1051         allows you to enter language numbers (as returned by the
1052         "Decode_Language()" function) or strings (as returned by the
1053         "Language_to_Text()" function), whatever you prefer.
1054
1055         The "language()" method (both class and object) always returns the
1056         NAME (one of ""Language_to_Text(1..Languages())"") of the current
1057         setting (and never its number).
1058
1059         BEWARE that in order to avoid possible conflicts between threads or
1060         modules running concurrently, you should NEVER use the global
1061         function "Language($lang);" or the class method
1062         "Date::Calc-"language($lang);> in this module!
1063
1064         The class method is retained only for backward compatibility and for
1065         convenience in stand-alone applications when it is guaranteed that no
1066         such conflicts can arise.
1067
1068         But you should probably avoid to use global settings anyway, because
1069         it may be especially troublesome to fix your code later when suddenly
1070         the need arises to use your code with threads or when your code needs
1071         to use other modules which also use "Date::Calc" (with different
1072         settings!).
1073
1074         By exclusively using local settings, you are making your code
1075         invulnerable against other, concurrent modules also using
1076         "Date::Calc" which still use global settings.
1077
1078       • Exported Functions
1079
1080         The "Date::Calc::Object" package imports ":all" functions exported by
1081         the "Date::Calc" module and re-exports them, for conveniency.
1082
1083         This allows you to write
1084
1085           use Date::Calc::Object qw(...);
1086
1087         instead of
1088
1089           use Date::Calc qw(...);
1090
1091         but with exactly the same semantics. The difference is that the
1092         object-oriented frontend is loaded additionally in the first case.
1093
1094         As with "Date::Calc" you can use the ":all" tag to import all of
1095         "Date::Calc"'s functions:
1096
1097           use Date::Calc::Object qw(:all);
1098
1099         In addition to the functions exported by "Date::Calc", the
1100         "Date::Calc::Object" package offers some utility functions of its own
1101         for export:
1102
1103             $year                          = shift_year(\@_);
1104             ($year,$mm,$dd)                = shift_date(\@_);
1105             ($hrs,$min,$sec)               = shift_time(\@_);
1106             ($year,$mm,$dd,$hrs,$min,$sec) = shift_datetime(\@_);
1107
1108         These functions enable your subroutines or methods to accept a
1109         "Date::Calc" (or subclass) date object, an (anonymous) array or a
1110         list (containing the necessary values) as parameters INTERCHANGEABLY.
1111
1112         You can import all of these auxiliary functions by using an ":aux"
1113         tag:
1114
1115           use Date::Calc::Object qw(:aux);
1116
1117         If you want to import both all of the "Date::Calc" functions as well
1118         as all these auxiliary functions, use the ":ALL" tag:
1119
1120           use Date::Calc::Object qw(:ALL);
1121
1122       • Subclassing
1123
1124         In case you want to subclass "Date::Calc" objects and to add new
1125         attributes of your own, it is recommended that you proceed as follows
1126         (the following will be considered as a part of the module's "contract
1127         of use" - which might be subject to change in the future, however):
1128
1129         Define a constant for the index of each attribute you want to add,
1130         currently starting no lower than "4", at the top of your subclass:
1131
1132             use constant ATTRIB1 => 4;
1133             use constant ATTRIB2 => 5;
1134             use constant ATTRIB3 => 6;
1135             ...
1136
1137         It is recommended that you use constants (which are easy to change),
1138         because I someday might want to require the element with index "4"
1139         for a new attribute of my own... ":-)"
1140
1141         Then access your attributes like so (e.g. after calling ""$self =
1142         SUPER->new();"" in your constructor method):
1143
1144             $self->[0][ATTRIB1] = 'value1';
1145             $self->[0][ATTRIB2] = 'value2';
1146             $self->[0][ATTRIB3] = 'value3';
1147             ...
1148
1149         Beware that if you put anything other than numbers or strings into
1150         your attributes, the methods "clone()" and "copy()" might not work as
1151         expected anymore!
1152
1153         Especially if your attributes contain references to other data
1154         structures, only the references will be copied, but not the data
1155         structures themselves.
1156
1157         This may not be what you want.
1158
1159         (You will have to override these two methods and write some of your
1160         own if not.)
1161
1162         In order for the overloaded operators and the "shift_*()" auxiliary
1163         functions from the "Date::Calc::Object" package to work properly (the
1164         latter of which are heavily used in the "Date::Calendar[::Year]"
1165         modules, for instance), the package name of your subclass (= the one
1166         your objects will be blessed into) is REQUIRED to contain a "::".
1167
1168         Note that you should ONLY subclass "Date::Calc", NEVER
1169         "Date::Calc::Object", since subclassing the latter is less efficient
1170         (because "Date::Calc::Object" is just an empty class which inherits
1171         from "Date::Calc" - subclassing "Date::Calc::Object" would thus just
1172         introduce an additional name space layer to search during Perl's
1173         runtime method binding process).
1174
1175         If you give your subclass a package name below/inside the "Date::"
1176         namespace, you will also benefit from the fact that all error
1177         messages produced by the "Date::Calc[::Object]" module (and also the
1178         "Date::Calendar[::Year]" modules, by the way) will appear to have
1179         originated from the place outside of all ""/^Date::/"" modules
1180         (including yours) where one of the "Date::" modules was first called
1181         - i.e., all errors are always blamed on the user, no matter how
1182         deeply nested inside the "Date::" modules they occur, and do not
1183         usually refer to places inside any of the "Date::" modules (this
1184         assumes that there are no bugs in the "Date::" modules, and that all
1185         errors are always the user's fault ":-)").
1186
1187         Moreover, your module's own error messages will behave in the same
1188         way if you ""use Carp::Clan qw(^Date::);"" at the top of your module
1189         and if you produce all error messages using "carp()" and "croak()"
1190         (instead of "warn()" and "die()", respectively).
1191

EXAMPLES

1193       1)
1194            # Switch to summer time:
1195            $now = Date::Calc->now();
1196            if (($now ge [2000,3,26,2,0,0]) and
1197                ($now lt [2000,3,26,3,0,0]))
1198            {
1199                $now += [0,0,0,1,0,0];
1200            }
1201
1202       2)
1203            use Date::Calc::Object qw(:all);
1204
1205            Date::Calc->date_format(3);
1206
1207            $date = 0;
1208            while (!$date)
1209            {
1210                print "Please enter the date of your birthday (day-month-year): ";
1211                $date = Date::Calc->new( Decode_Date_EU( scalar(<STDIN>) ) );
1212                if ($date)
1213                {
1214                    $resp = 0;
1215                    while ($resp !~ /^\s*[YyNn]/)
1216                    {
1217                        print "Your birthday is: $date\n";
1218                        print "Is that correct? (yes/no) ";
1219                        $resp = <STDIN>;
1220                    }
1221                    $date = 0 unless ($resp =~ /^\s*[Yy]/)
1222                }
1223                else
1224                {
1225                    print "Unable to parse your birthday. Please try again.\n";
1226                }
1227            }
1228
1229            if ($date + [18,0,0] <= [Today()])
1230                { print "Ok, you are over 18.\n"; }
1231            else
1232                { print "Sorry, you are under 18!\n"; }
1233
1234       For more examples, see the "examples" subdirectory in this
1235       distribution, and their descriptions in the file "EXAMPLES.txt".
1236

SEE ALSO

1238       Date::Calc(3), Date::Calc::Util(3), Date::Calendar(3),
1239       Date::Calendar::Year(3), Date::Calendar::Profiles(3).
1240

VERSION

1242       This man page documents "Date::Calc::Object" version 6.4.
1243

AUTHOR

1245         Steffen Beyer
1246         mailto:STBEY@cpan.org
1247         http://www.engelschall.com/u/sb/download/
1248
1250       Copyright (c) 2000 - 2015 by Steffen Beyer. All rights reserved.
1251

LICENSE

1253       This package is free software; you can use, modify and redistribute it
1254       under the same terms as Perl itself, i.e., at your option, under the
1255       terms either of the "Artistic License" or the "GNU General Public
1256       License".
1257
1258       The C library at the core of the module "Date::Calc::XS" can, at your
1259       discretion, also be used, modified and redistributed under the terms of
1260       the "GNU Library General Public License".
1261
1262       Please refer to the files "Artistic.txt", "GNU_GPL.txt" and
1263       "GNU_LGPL.txt" in the "license" subdirectory of this distribution for
1264       any details!
1265

DISCLAIMER

1267       This package is distributed in the hope that it will be useful, but
1268       WITHOUT ANY WARRANTY; without even the implied warranty of
1269       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
1270
1271       See the "GNU General Public License" for more details.
1272
1273
1274
1275perl v5.32.1                      2021-01-27             Date::Calc::Object(3)
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