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

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

       Make frequent things easy and infrequent or hard things possible

       Note that you do NOT need to ""use Date::Calc qw(...);"" in addition to
       this module.


	 use Date::Calc::Object qw(...);


	 use Date::Calc qw(...);

       with the same ""qw(...)"" as you would with the "Date::Calc" module,
       and then forget about "Date::Calc::Object" altogether.

       The rest of your existing code doesn't change at all.

       Note also that in order to create a new date object, you do not need to

	 $date_object = Date::Calc::Object->new(...);

       (but you may), and should use

	 $date_object = Date::Calc->new(...);

       instead (saves you some typing and is a trifle faster).

   Export tags
	 :all  -  all functions from Date::Calc
	 :aux  -  auxiliary functions shift_*
	 :ALL  -  both :all and :aux

       See Date::Calc(3) for a list of available functions.

	 $year				= shift_year(\@_);
	 ($year,$mm,$dd)		= shift_date(\@_);
	 ($hrs,$min,$sec)		= shift_time(\@_);
	 ($year,$mm,$dd,$hrs,$min,$sec) = shift_datetime(\@_);

	 $old = Date::Calc->accurate_mode([FLAG]);
	 $old = Date::Calc->normalized_mode([FLAG]);
	 $old = Date::Calc->number_format([NUMBER|CODEREF]);
	 $old = Date::Calc->delta_format([NUMBER|CODEREF]);  # global default
	 $old = Date::Calc->date_format([NUMBER|CODEREF]);   # global default
	 $old = Date::Calc->language([LANGUAGE]);	     # global default - DEPRECATED

	 $old = $date->accurate_mode([FLAG]);		# is global nevertheless!
	 $old = $date->normalized_mode([FLAG]);		# is global nevertheless!
	 $old = $date->number_format([NUMBER|CODEREF]); # is global nevertheless!
	 $old = $date->delta_format([NUMBER|CODEREF]);	# individual override
	 $old = $date->date_format([NUMBER|CODEREF]);	# individual override
	 $old = $date->language([LANGUAGE]);		# individual override

	 $flag = $date->is_delta();
	 $flag = $date->is_date();
	 $flag = $date->is_short(); # i.e., has no time part
	 $flag = $date->is_long();  # i.e., has time part
	 $flag = $date->is_valid();

	 $date = Date::Calc->new([TYPE]);
	 $date = Date::Calc->new([TYPE,]YEAR,MONTH,DAY[,HRS,MIN,SEC]);
	 $date = Date::Calc->new($arrayref);
	 $newdate = $somedate->new([TYPE]);
	 $newdate = $somedate->new([TYPE,]YEAR,MONTH,DAY[,HRS,MIN,SEC]);
	 $newdate = $somedate->new($arrayref);

	 $datecopy = $date->clone();

	 ($year,$month,$day) = $date->date([TYPE]);
	 ($year,$month,$day) = $date->date([TYPE,]YEAR,MONTH,DAY[,HRS,MIN,SEC]);
	 ($year,$month,$day) = $date->date($arrayref);
	 ([$hrs,$min,$sec])  = $date->time([TYPE]);
	 ($hrs,$min,$sec)    = $date->time([TYPE,]HRS,MIN,SEC);
	 ([$hrs,$min,$sec])  = $date->time($arrayref);

	 ($year,$month,$day,$hrs,$min,$sec) =
	 ($year,$month,$day,$hrs,$min,$sec) =

	 $date	= Date::Calc->today([FLAG]);
	 $date	= Date::Calc->now([FLAG]); # shorthand for --+
	 $date	= Date::Calc->today_and_now([FLAG]); # <-----+
	 $date	= Date::Calc->gmtime([time]);	 # UTC/GMT
	 $date	= Date::Calc->localtime([time]); # local time
	 $delta = Date::Calc->tzoffset([time]);
	 $date	= Date::Calc->time2date([time]); # UTC/GMT

	 $date->today([FLAG]);	       # updates the date part only
	 $date->now([FLAG]);	       # updates the time part only
	 $date->today_and_now([FLAG]); # updates both date and time
	 $date->gmtime([time]);	       # updates both date and time (UTC/GMT)
	 $date->localtime([time]);     # updates both date and time (local time)
	 $delta->tzoffset([time]);     # updates both date and time
	 $date->time2date([time]);     # updates both date and time (UTC/GMT)

	 $time = Date::Calc->mktime();	  # same as "$time = CORE::time();"
	 $time = Date::Calc->date2time(); # same as "$time = CORE::time();"

	 $time = $date->mktime();      # converts into Unix time (local time)
	 $time = $date->date2time();   # converts into Unix time (UTC/GMT)

	 $year	  = $date->year([YEAR]);
	 $month	  = $date->month([MONTH]);
	 $day	  = $date->day([DAY]);
	 $hours	  = $date->hours([HRS]);
	 $minutes = $date->minutes([MIN]);
	 $seconds = $date->seconds([SEC]);

	 $number = $date->number([NUMBER|CODEREF]);
	 $string = $date->string([NUMBER|CODEREF][,LANGUAGE]);

	 $delta->normalize(); # renormalizes a delta vector

   Overloaded Operators
	 # Scalar operands are always converted into a delta #
	 # vector with that many days, i.e., [1,0,0,SCALAR]  #

   Comparison Operators:
	 if ($date1 <  $date2) { # compares date part only
	 if ($date1 <= $date2) { # compares date part only
	 if ($date1 >  $date2) { # compares date part only
	 if ($date1 >= $date2) { # compares date part only
	 if ($date1 == $date2) { # compares date part only
	 if ($date1 != $date2) { # compares date part only

	 $comp = $date1 <=> $date2; # compares date part only

	 if ($date1 lt $date2) { # compares both date and time
	 if ($date1 le $date2) { # compares both date and time
	 if ($date1 gt $date2) { # compares both date and time
	 if ($date1 ge $date2) { # compares both date and time
	 if ($date1 eq $date2) { # compares both date and time
	 if ($date1 ne $date2) { # compares both date and time

	 $comp = $date1 cmp $date2; # compares both date and time

       Note that you can of course also compare two deltas, but not a date and
       a delta!

	 # Default TYPE for array refs in comparisons is: #
	 # Same as other operand			  #

	 if ([2000,4,1] == $date) {
	 if ($today > [2000,4,1]) {

	 if ($now ge [2000,3,26,2,0,0]) {

	 if ($delta == [18,0,0]) {
	 if ($delta == -1) {

	 $date2 = $date1 + $delta;
	 $date2 = $delta + $date1;
	 $date += $delta;
	 $this = $date++;
	 $next = ++$date;

	 $delta3 = $delta1 + $delta2;
	 $delta1 += $delta2;
	 $delta += $date; # beware of implicit type change!

	 # Default TYPE for array refs in '+' operations is: #
	 # Opposite of other operand			     #

	 $date2 = [2000,3,26] + $delta;
	 $date2 = $date1 + [+1,0,0];
	 $date2 = [0,0,-1] + $date1;
	 $date2 = $date1 + 1;
	 $date += [0,0,+1];
	 $date += 2;

	 $delta3 = [1,+1,0,-1] + $delta2;
	 $delta3 = $delta1 + [1,0,0,+1];
	 $delta3 = $delta1 + 1;
	 $delta += [1,0,+1,0];
	 $delta += [2000,3,26]; # beware of implicit type change!
	 $delta += 7;

   Unary Minus:
	 $delta2 = -$delta1;

	 $delta = $date2 - $date1;
	 $date2 = $date1 - $delta;
	 $date -= $delta;
	 $date2 -= $date1; # beware of implicit type change!
	 $this = $date--;
	 $prev = --$date;

	 $delta3 = $delta2 - $delta1;
	 $delta2 -= $delta1;

	 # Default TYPE for array refs in '-' operations is: #
	 # Always a date				     #

	 $delta = $today - [2000,3,26];
	 $delta = [2000,4,1] - $date;
	 $date2 = [2000,3,26] - $delta;
	 $date2 = $date1 - [1,0,0,+7];
	 $date2 = $date1 - 7;
	 $date -= [1,0,0,+1]; # better add [0,0,-1] instead!
	 $date2 -= [2000,3,26]; # beware of implicit type change!
	 $date2 -= 1;

	 $delta3 = [1,0,+1,0] - $delta1;
	 $delta3 = $delta2 - [1,0,0,-1];
	 $delta -= [1,0,0,+1];
	 $delta -= 7;

   Miscellaneous Operators:
	 $string = "$date";
	 $string = "$delta";

	 print "$date\n";
	 print "$delta\n";

	 if ($date) { # date is valid
	 if ($delta) { # delta is valid

	 $days = abs($date);
	 $diff = abs($delta); # can be negative!

	 $diff = abs(abs($delta)); # always positive

       · FLAG

	 "FLAG" is either 0 (for "false") or 1 (for "true").

	 In the case of ""accurate_mode()"" and ""normalized_mode()"", this
	 switches the corresponding mode on and off (see further below for an
	 explanation of what these are).

	 In the case of ""today()"", ""now()"" and ""today_and_now()"", a
	 "true" value indicates "GMT" (Greenwich Mean Time), as opposed to
	 local time, which is the default.

       · NUMBER

	 "NUMBER" is a number between 0 and 2 (for "number_format()" and
	 "number()") or between 0 and 4 (for "delta_format()", "date_format()"
	 and "string()"), indicating which of the three/five predefined
	 formats, respectively, should be used for converting a date into
	 numeric representation (needed for comparing dates, for instance) or
	 string representation.

	 Format #0 is the default at startup and the simplest of all (and
	 should be fastest to calculate, too).

	 The string representation of dates in format #0 also has the
	 advantage of being sortable in chronological order (and of complying
	 with ISO 8601).

	 (The numeric formats are (trivially) always sortable in chronological
	 order of course.)

	 The other formats are (mostly) increasingly more sophisticated (in
	 terms of esthetics and computation time) with increasing number
	 (except for format #4):

	   Delta number formats (short):

	       0    13603
	       1    13603
	       2    13603

	   Delta string formats (short):

	       0    '+0+0+13603'
	       1    '+0 +0 +13603'
	       2    '+0Y +0M +13603D'
	       3    '+0 Y +0 M +13603 D'
	       4    '(0,0,13603)'

	   Date number formats (short):

	       0    20010401
	       1    730576
	       2    730576

	   Date string formats (short):

	       0    '20010401'
	       1    '01-Apr-2001'
	       2    'Sun 1-Apr-2001'
	       3    'Sunday, April 1st 2001'
	       4    '[2001,4,1]'

	   Delta number formats (long):

	       0    13603.012959
	       1    13603.012959
	       2    13603.0624884259

	   Delta string formats (long):

	       0    '+0+0+13603+1+29+59'
	       1    '+0 +0 +13603 +1 +29 +59'
	       2    '+0Y +0M +13603D +1h +29m +59s'
	       3    '+0 Y +0 M +13603 D +1 h +29 m +59 s'
	       4    '(0,0,13603,1,29,59)'

	   Date number formats (long):

	       0    20010401.082959
	       1    730576.082959
	       2    730576.354155093

	   Date string formats (long):

	       0    '20010401082959'
	       1    '01-Apr-2001 08:29:59'
	       2    'Sun 1-Apr-2001 08:29:59'
	       3    'Sunday, April 1st 2001 08:29:59'
	       4    '[2001,4,1,8,29,59]'

	 If a number outside of the permitted range is specified, or if the
	 value is not a code reference (see also the next section below for
	 more details), the default format #0 is used instead.

       · CODEREF

	 "CODEREF" is the reference of a subroutine which can be passed to the
	 methods "number_format()", "delta_format()" and "date_format()" in
	 order to install a callback function which will be called
	 subsequently whenever a date (or delta) object needs to be
	 (implicitly) converted into a number or string.

	 This happens for instance when you compare two date objects, or when
	 you put a date object reference in a string between double quotes.

	 Such a "CODEREF" can also be passed to the methods "number()" and
	 "string()" for explicitly converting a date object as desired.

       · LANGUAGE

	 "LANGUAGE" is either a number in the range "[1..Languages()]", or one
	 of the strings ""Language_to_Text(1..Languages())"" (see also

       · TYPE

	 "TYPE" is 0 for a regular date and 1 for a delta vector (a list of
	 year, month, day and optionally hours, minutes and seconds offsets).

       · Storage

	 "Date::Calc" objects are implemented as two nested arrays.

	 The "blessed" array (whose reference is the object reference you
	 receive when calling the "new()" method) contains an anonymous array
	 at position zero and the object's data in its remaining fields.

	 The embedded anonymous array is used for storing the object's
	 attributes (flags).

	 Dates and delta vectors always comprise either 3 or 6 data values:
	 Year, month, day plus (optionally) hours, minutes and seconds.

	 These values are stored in the "blessed" array at positions 1..3 or
	 1..6, respectively.

	 An object without the time values is therefore called "short", and an
	 object having time values is called "long" throughout this manual.

	 Hint: Whenever possible, if you do not need the time values, omit
	 them, i.e., always use the "short" form of the object if possible,
	 this will speed up calculations a little (the short form uses
	 different (faster) functions for all calculations internally).

	 The embedded anonymous array contains various flags:

	 At position zero, it contains the "TYPE" indicator which determines
	 whether the object is a date or a delta vector.

	 At position 1, the object stores the "NUMBER" of one of the delta
	 vector formats, or the reference of a callback function which
	 converts the contents of the object into string representation if
	 it's a delta vector, or "undef" if the global settings apply.

	 At position 2, the object stores the "NUMBER" of one of the date
	 formats, or the reference of a callback function which converts the
	 contents of the object into string representation if it's a date, or
	 "undef" if the global settings apply.

	 At position 3, the object stores the "LANGUAGE" to be used for all
	 conversions into strings (where applicable), or "undef" if the global
	 language setting applies.

	 Note that your callback functions (see the section "Callback
	 Functions" further below for more details) should not pay attention
	 to this value at position 3, because they get a parameter which tells
	 them which language to use (this is necessary in order to allow
	 temporary overrides).

	 If your callback handlers use the "*_to_Text*" functions (or any
	 other language-dependent function) from the "Date::Calc" module, your
	 handlers should pass on this language parameter to these functions
	 (and not the value from position 3).

	 Be reminded though that you should NEVER access the object's internal
	 data directly, i.e., through their positional numbers, but ALWAYS
	 through their respective accessor methods, e.g.:


	 And although position 4 and onward in the embedded anonymous array is
	 currently unused, it might not stay so in future releases of this

	 Therefore, in case you need more attributes in a subclass of the
	 "Date::Calc[::Object]" class, I suggest using values starting at
	 positions a bit further up, e.g. 6, 8 or 10.

       · Invalid Dates

	 Only "new()" allows to create objects containing possibly invalid
	 dates (needed for reading in and evaluating user input, for example).

       · Usage

	 The methods


	 are used for reading as well as for setting attributes. They simply
	 return the values in question if they are called without parameters.

	 The methods


	 always return the previous value if a new value is set. This allows
	 you to change these values temporarily and to restore their old value
	 afterwards more easily (but you can also override the "format" and
	 "language" settings directly when calling the "number()" or
	 "string()" method).

	 The methods


	 always return the new values when the corresponding values have been

	 The method "date()" NEVER returns the time values (hours, minutes,
	 seconds) even if they have just been set using this method (which the
	 method optionally allows). Otherwise it would be very hard to predict
	 the exact number of values it returns, which might lead to errors
	 (wrong number of parameters) elsewhere in your program.

	 The method "datetime()" ALWAYS returns the time values (hours,
	 minutes, seconds) even if the object in question lacks a time part.
	 In that case, zeros are returned for hours, minutes and seconds
	 instead (but the stored time part is left unchanged, whether it
	 exists or not).

	 If you do not provide values for hours, minutes and seconds when
	 using the method "date()" to set the values for year, month and day,
	 the time part will not be changed (whether it exists or not).

	 If you do not provide values for hours, minutes and seconds when
	 using the method "datetime()" to set the values for year, month and
	 day, the time part will be filled with zeros (the time part will be
	 created if necessary).

	 If the object is short, i.e., if it does not have any time values,
	 the method "time()" returns an empty list.

	 If the object is short and the methods "hours()", "minutes()" or
	 "seconds()" are used to set any of these time values, the object is
	 automatically promoted to the "long" form, and the other two time
	 values are filled with zeros.

	 The following methods can also return "undef" under certain


	 The methods "delta_format()", "date_format()" and "language()" return
	 "undef" when they are called as object methods and no individual
	 override has been defined for the object in question.

	 The "is_*()" predicate methods return "undef" if the object in
	 question does not have the expected internal structure. This can
	 happen for instance when you create an empty object with "new()".

	 When called without parameters, the methods "hours()", "minutes()"
	 and "seconds()" return "undef" if the object in question does not
	 have a time part.

	 The methods "number()" and "string()" return "undef" if the object in
	 question is not valid (i.e., if "is_valid()" returns "undef" or

	 And finally, the methods


	 return the object reference of the (target) object in question for

       · Import/Export

	 Note that you can import and export Unix "time" values using the
	 methods "gmtime()", "localtime()", "mktime()", "date2time()" and
	 "time2date()", both as local time or as UTC/GMT.

       · Accurate Mode and Normalized Mode

	 The method "accurate_mode()" controls the internal flag which
	 determines which of two fundamental modes of operation is used.

	 When set to true (the default at startup), delta vectors are
	 calculated to give the exact difference in days between two dates.
	 The "year" and "month" entries in the resulting delta vector are
	 always zero in that case.

	 If "accurate mode" is switched off (when the corresponding flag is
	 set to false), delta vectors are calculated with year and month

	 E.g., the difference between "[1999,12,6]" and "[2000,6,24]" is "[+0
	 +0 +201]" (plus 201 days) in accurate mode and "[+1 -6 +18]" (plus
	 one year, minus 6 months, plus 18 days) when accurate mode is
	 switched off, and is "[+0 +6 +18]" (plus 6 months, plus 18 days) if
	 additionally, "normalized mode" is switched on.

	 The delta vector is calculated by simply taking the difference in
	 years, the difference in months and the difference in days (if
	 "accurate mode" is switched off and if "normalized mode" has not been
	 switched on). This is called "one-by-one" semantics or "year-month-
	 day mode"; "YMD mode" for short.

	 When "normalized mode" is switched on (while "accurate mode" is
	 switched off), the delta vector is calculated in a more complex way
	 involving the functions ""Add_Delta_YM()"" (for "truncation") and

	 Moreover, the result is normalized, i.e., the return values are
	 guaranteed to all have the same sign (or to be zero), and to all be
	 "minimal", i.e., not to exceed the ranges "[-11..+11]" for months,
	 "[-30..+30]" for days, "[-23..+23]" for hours and "[-59..+59]" for
	 minutes and seconds.

	 The rule is to add these result values to a date in a left-to-right
	 order, and to truncate invalid intermediate dates, such as e.g.
	 "[2009,2,29]", to the last valid day of that same month, e.g.
	 "[2009,2,28]". This is called "left-to-right with truncation"
	 semantics or "normalized mode"; "N_YMD mode" for short.

	 The method "normalized_mode()" controls the internal flag which
	 determines whether "YMD mode" is used (the default at startup, for
	 reasons of backward compatibility) or "N_YMD mode".

	 Note that also for reasons of backward compatibility, this flag only
	 has effect when "accurate mode" is switched off.

	 Both flags can be set and reset independently from each other,

	 Therefore, at startup, you can for instance switch "normalized mode"
	 on, without having any immediate effect, and switch off "accurate
	 mode" later, which instantly also causes "normalized mode" to spring
	 into effect.

	 Because years and months have varying lengths in terms of days, the
	 "YMD" and "N_YMD" modes are less accurate than "accurate mode",
	 because these modes depend on the context of the two dates of which
	 the delta vector is the difference. Added to a different date, a
	 delta vector calculated in "YMD mode" or "N_YMD mode" may yield a
	 different offset in terms of days, i.e., the final result may
	 sometimes vary seemingly unpredictably (or in other situations may
	 give you the expected result, at the expense of actually representing
	 a varying difference in days, determined exclusively by context).

	 Beware also that - for the same reason - the absolute value
	 (""abs()"") of a delta vector returns a fictitious number of days if
	 the delta vector contains non-zero values for "year" and/or "month"
	 (see also the next section "Absolute Value" below for more details).


	 The difference between "[2000,1,1]" and "[2000,3,1]" is "[+0 +0 +60]"
	 in "accurate mode" and "[+0 +2 +0]" in "YMD mode" (in this "benign"
	 example, the result is the same in "YMD mode" and in "N_YMD mode").

	 When added to the date "[2000,4,1]", the "accurate" delta vector
	 yields the date "[2000,5,31]", whereas the "YMD mode" delta vector
	 yields the date "[2000,6,1]" (which is actually a difference of 61

	 Moreover, when added to the date "[1999,1,1]", the "accurate" delta
	 vector yields the date "[1999,3,2]", whereas the "inaccurate" "YMD
	 Mode" delta vector yields the date "[1999,3,1]" (which is actually a
	 difference of 59 days).

	 Depending on what you want, either mode may suit you better.

       · Absolute Value

	 Note that ""abs($date)"" and ""abs($delta)"" are just shorthands for
	 ""$date->number()"" and ""$delta->number()"".

	 The operator ""abs()"", when applied to a date or delta vector,
	 returns the corresponding number of days (see below for an exception
	 to this), with the time part (if available) represented by a fraction
	 after the decimal point.

	 In the case of dates, the absolute value (to the left of the decimal
	 point) is the number of days since the 1st of January 1 A.D. (by
	 extrapolating the Gregorian calendar back beyond its "natural" limit
	 of 1582 A.D.) PLUS ONE.

	 (I.e., the absolute value of the 1st of January 1 A.D. is 1.)


	 If the "NUMBER" or "number_format()" is set to 0 (the default
	 setting), the absolute value of a date to the left of the decimal
	 point is "yyyymmdd", i.e., the number in which the uppermost four
	 digits correspond to the year, the next lower two digits to the month
	 and the lowermost two digits to the day.

	 In the case of delta vectors, the absolute value (to the left of the
	 decimal point) is simply the difference in days (but see also below).

	 Note that the absolute value of a delta vector can be negative!

	 If you want a positive value in all cases, apply the ""abs()""
	 operator again, i.e., ""$posdiff = abs(abs($delta));"".

	 If the delta vector contains non-zero values for "year" and/or
	 "month" (see also the discussion of "Accurate Mode" in the section
	 above), an exact representation in days cannot be calculated, because
	 years and months do not have fixed equivalents in days.

	 If nevertheless you attempt to calculate the absolute value of such a
	 delta vector, a fictitious value is returned, which is calculated by
	 simply multiplying the year difference with 12, adding the month
	 difference, multiplying this sum with 31 and finally adding the day

	 Beware that because of this, the absolute values of delta vectors are
	 not necessarily contiguous.

	 Moreover, since there is more than one way to express the difference
	 between two dates, comparisons of delta vectors may not always yield
	 the expected result.


	 The difference between the two dates "[2000,4,30]" and "[2001,5,1]"
	 can be expressed as "[+1 +1 -29]", or as "[+1 +0 +1]".

	 The first delta vector has an absolute value of 374, whereas the
	 latter delta vector has an absolute value of only 373 (while the true
	 difference in days between the two dates is 366).

	 If the date or delta vector has a time part, the time is returned as
	 a fraction of a full day after the decimal point as follows:

	 If the "NUMBER" or "number_format()" is set to 0 (the default
	 setting) or 1, this fraction is simply ".hhmmss", i.e., the two
	 digits after the decimal point represent the hours, the next two
	 digits the minutes and the last two digits the seconds.

	 Note that you cannot simply add and subtract these values to yield
	 meaningful dates or deltas again, you can only use them for
	 comparisons (equal, not equal, less than, greater than, etc.). If you
	 want to add/subtract, read on:

	 Only when the "NUMBER" or "number_format()" is set to 2, this
	 fraction will be the equivalent number of seconds (i.e., "(((hours *
	 60) + minutes) * 60) + seconds") divided by the number of seconds in
	 a full day (i.e., "24*60*60 = 86400"), or "0/86400", "1/86400", ... ,

	 In other words, the (mathematically correct) fraction of a day.

	 You can safely perform arithmetics with these values as far as the
	 internal precision of your vendor's implementation of the C run-time
	 library (on which Perl depends) will permit.

       · Renormalizing Delta Vectors

	 When adding or subtracting delta vectors to/from one another, the
	 addition or subtraction takes place component by component.


	   [+0 +0 +0 +3 +29 +50] + [+0 +0 +0 +0 +55 +5] = [+0 +0 +0 +3 +84 +55]
	   [+0 +0 +0 +3 +29 +50] - [+0 +0 +0 +0 +55 +5] = [+0 +0 +0 +3 -26 +45]

	 This may result in time values outside the usual ranges ("[-23..+23]"
	 for hours and "[-59..+59]" for minutes and seconds).

	 Note that even though the delta value for days will often become
	 quite large, it is impossible to renormalize this value because there
	 is no constant conversion factor from days to months (should it be
	 28, 29, 30 or 31?).

	 If accurate mode (see further above for what that is) is switched
	 off, delta vectors can also contain non-zero values for years and
	 months. If you add or subtract these, the value for months can lie
	 outside the range "[-11..11]", which isn't wrong, but may seem funny.

	 Therefore, the "normalize()" method will also renormalize the
	 "months" value, if and only if accurate mode has been switched off.

	 (Hence, switch accurate mode ON temporarily if you DON'T want the
	 renormalization of the "months" value to happen.)

	 If you want to force the time values from the example above back into
	 their proper ranges, use the "normalize()" method as follows:

	   print "[$delta]\n";
	   print "[$delta]\n";

	 This will print

	   [+0 +0 +0 +3 +84 +55]
	   [+0 +0 +0 +4 +24 +55]

	 for the first and

	   [+0 +0 +0 +3 -26 +45]
	   [+0 +0 +0 +2 +34 +45]

	 for the second delta vector from the example further above.

	 Note that the values for days, hours, minutes and seconds are
	 guaranteed to have the same sign after the renormalization.

	 Under "normal" circumstances, i.e., when accurate mode is on (the
	 default), this method only has an effect on the time part of the
	 delta vector.

	 If the delta vector in question does not have a time part, nothing

	 If accurate mode is off, the "months" value is also normalized, i.e.,
	 if it lies outside of the range "[-11..11]", integer multiples of 12
	 are added to the "years" value and subtracted from the "months"
	 value. Moreover, the "months" value is guaranteed to have the same
	 sign as the values for days, hours, minutes and seconds, unless the
	 "months" value is zero or the values for days, hours, minutes and
	 seconds are all zero.

	 If the object in question is a date and if warnings are enabled, the
	 message "normalizing a date is a no-op" will be printed to STDERR.

	 If the object in question is not a valid "Date::Calc" object, nothing

	 The method returns its object's reference, which allows chaining of
	 method calls, as in the following example:

	   @time = $delta->normalize()->time();

       · Callback Functions

	 Note that you are not restricted to the built-in formats (numbered
	 from 0 to 2 for "number_format()" and "number()" and from 0 to 4 for
	 "delta_format()", "date_format()" and "string()") for converting a
	 date or delta object into a number or string.

	 You can also provide your own function(s) for doing so, in order to
	 suit your own taste or needs, by passing a subroutine reference to
	 the appropriate method, i.e., "number_format()", "number()",
	 "delta_format()", "date_format()" and "string()".

	 You can pass a handler to only one or more of these methods, or to
	 all of them, as you like. You can use different callback functions,
	 or the same for all.

	 In order to facilitate the latter, and in order to make the decoding
	 of the various cases easier for you, the callback function receives a
	 uniquely identifying function code as its second parameter:

	   0  =	 TO_NUMBER | IS_DATE  | IS_SHORT  (number[_format])
	   1  =	 TO_NUMBER | IS_DATE  | IS_LONG	  (number[_format])
	   2  =	 TO_NUMBER | IS_DELTA | IS_SHORT  (number[_format])
	   3  =	 TO_NUMBER | IS_DELTA | IS_LONG	  (number[_format])
	   4  =	 TO_STRING | IS_DATE  | IS_SHORT  (string|date_format)
	   5  =	 TO_STRING | IS_DATE  | IS_LONG	  (string|date_format)
	   6  =	 TO_STRING | IS_DELTA | IS_SHORT  (string|delta_format)
	   7  =	 TO_STRING | IS_DELTA | IS_LONG	  (string|delta_format)

	 The first parameter of the callback function is of course the
	 reference of the object in question itself (therefore, the callback
	 function can actually be an object method - but not a class method,
	 for obvious reasons).

	 The third parameter is the number of the language (in the range
	 "[1..Languages()]") which you should always pass along when using any
	 of the following functions from the "Date::Calc" module in your

	 "Decode_Month()", "Decode_Day_of_Week()", "Compressed_to_Text()",
	 "Date_to_Text()", "Date_to_Text_Long()", "Calendar()",
	 "Month_to_Text()", "Day_of_Week_to_Text()",
	 "Day_of_Week_Abbreviation()", "Decode_Date_EU()", "Decode_Date_US()",
	 "Decode_Date_EU2()", "Decode_Date_US2()", "Parse_Date()".

	 The callback handler should return the resulting number or string, as

	 BEWARE that you should NEVER rely upon any knowledge of the object's
	 internal structure, as this may be subject to change!

	 ALWAYS use the test and access methods provided by this module!


	   sub handler
	       my($self,$code,$lang) = @_;

	       if    ($code == 0) # TO_NUMBER | IS_DATE	 | IS_SHORT
		   return Date_to_Days( $self->date() );
	       elsif ($code == 1) # TO_NUMBER | IS_DATE	 | IS_LONG
		   return Date_to_Days( $self->date() ) +
				    ( ( $self->hours() * 60 +
					$self->minutes() ) * 60 +
					$self->seconds() ) / 86400;
	       elsif ($code == 2) # TO_NUMBER | IS_DELTA | IS_SHORT
		   return ( $self->year() * 12 +
			    $self->month() ) * 31 +
	       elsif ($code == 3) # TO_NUMBER | IS_DELTA | IS_LONG
		   return ( $self->year() * 12 +
			    $self->month() ) * 31 +
			    $self->day() +
			( ( $self->hours() * 60 +
			    $self->minutes() ) * 60 +
			    $self->seconds() ) / 86400;
	       elsif ($code == 4) # TO_STRING | IS_DATE	 | IS_SHORT
		   return join( "/", $self->date() );
	       elsif ($code == 5) # TO_STRING | IS_DATE	 | IS_LONG
		   return join( "/", $self->date() ) . " " .
			  join( ":", $self->time() );
	       elsif ($code == 6) # TO_STRING | IS_DELTA | IS_SHORT
		   return join( "|", $self->date() );
	       elsif ($code == 7) # TO_STRING | IS_DELTA | IS_LONG
		   return join( "|", $self->datetime() );
		   die "internal error";


	 This sets our handler to take care of all automatic conversions, such
	 as needed when comparing dates or when interpolating a string in
	 double quotes which contains a date object.

	 To deactivate a handler, simply pass a valid format number to the
	 method in question, e.g.:


	 When calling the "number()" or "string()" method explicitly, you can
	 pass a different format number (than the global setting), like this:

	   $number = $date->number(2);
	   $string = $date->string(1);

	 You can also pass a handler's reference, like so:

	   $number = $date->number(\&handler);
	   $string = $date->string(\&handler);

	 This overrides the global setting and the individual object's local
	 setting for the duration of the call of "number()" or "string()" (but
	 doesn't change the global or local settings themselves).

	 Moreover, you can also define individual overrides for the date and
	 the delta vector formats (but not the number format) for individual
	 objects, e.g.:



	 In order to deactivate an individual handler for an object, and/or in
	 order to deactivate any override altogether (so that the global
	 settings apply again), you have to pass "undef" explicitly to the
	 method in question:


	 You can also define a language for individual objects (see the next
	 section immediately below for more details).

	 If such an individual language override has been set, it will be
	 passed to your callback handlers as the third parameter (in the case
	 of "string" conversions, but not in the case of "number"

	 Otherwise, the global settings as defined by "Language($lang);" or
	 "Date::Calc-"language($lang);> will be passed to your handler.

       · Languages

	 Note that this module is completely transparent to the setting of a
	 language in "Date::Calc". This means that you can choose a language
	 in "Date::Calc" (with the "Language()" function) and all dates
	 subsequently printed by this module will automatically be in that
	 language - provided that you use the built-in formats of this module,
	 or that you pass the third parameter of the callback funtion to the
	 funtions of the "Date::Calc" module which accept it.

	 However, this global language setting can be overridden for
	 individual date (or delta) objects by using the OBJECT method

	     $oldlang = $date->language($newlang);

	 (The global setting is not altered by this in any way.)

	 In order to deactivate such an individual language setting (so that
	 the global setting applies again), simply pass the value "undef"
	 explicitly to the "language()" object method:


	 The CLASS method

	     $oldlang = Date::Calc->language($newlang);

	 is just a convenient wrapper around the "Language()" function, which
	 allows you to enter language numbers (as returned by the
	 "Decode_Language()" function) or strings (as returned by the
	 "Language_to_Text()" function), whatever you prefer.

	 The "language()" method (both class and object) always returns the
	 NAME (one of ""Language_to_Text(1..Languages())"") of the current
	 setting (and never its number).

	 BEWARE that in order to avoid possible conflicts between threads or
	 modules running concurrently, you should NEVER use the global
	 function "Language($lang);" or the class method
	 "Date::Calc-"language($lang);> in this module!

	 The class method is retained only for backward compatibility and for
	 convenience in stand-alone applications when it is guaranteed that no
	 such conflicts can arise.

	 But you should probably avoid to use global settings anyway, because
	 it may be especially troublesome to fix your code later when suddenly
	 the need arises to use your code with threads or when your code needs
	 to use other modules which also use "Date::Calc" (with different

	 By exclusively using local settings, you are making your code
	 invulnerable against other, concurrent modules also using
	 "Date::Calc" which still use global settings.

       · Exported Functions

	 The "Date::Calc::Object" package imports ":all" functions exported by
	 the "Date::Calc" module and re-exports them, for conveniency.

	 This allows you to write

	   use Date::Calc::Object qw(...);

	 instead of

	   use Date::Calc qw(...);

	 but with exactly the same semantics. The difference is that the
	 object-oriented frontend is loaded additionally in the first case.

	 As with "Date::Calc" you can use the ":all" tag to import all of
	 "Date::Calc"'s functions:

	   use Date::Calc::Object qw(:all);

	 In addition to the functions exported by "Date::Calc", the
	 "Date::Calc::Object" package offers some utility functions of its own
	 for export:

	     $year			    = shift_year(\@_);
	     ($year,$mm,$dd)		    = shift_date(\@_);
	     ($hrs,$min,$sec)		    = shift_time(\@_);
	     ($year,$mm,$dd,$hrs,$min,$sec) = shift_datetime(\@_);

	 These functions enable your subroutines or methods to accept a
	 "Date::Calc" (or subclass) date object, an (anonymous) array or a
	 list (containing the necessary values) as parameters INTERCHANGEABLY.

	 You can import all of these auxiliary functions by using an ":aux"

	   use Date::Calc::Object qw(:aux);

	 If you want to import both all of the "Date::Calc" functions as well
	 as all these auxiliary functions, use the ":ALL" tag:

	   use Date::Calc::Object qw(:ALL);

       · Subclassing

	 In case you want to subclass "Date::Calc" objects and to add new
	 attributes of your own, it is recommended that you proceed as follows
	 (the following will be considered as a part of the module's "contract
	 of use" - which might be subject to change in the future, however):

	 Define a constant for the index of each attribute you want to add,
	 currently starting no lower than "4", at the top of your subclass:

	     use constant ATTRIB1 => 4;
	     use constant ATTRIB2 => 5;
	     use constant ATTRIB3 => 6;

	 It is recommended that you use constants (which are easy to change),
	 because I someday might want to require the element with index "4"
	 for a new attribute of my own... ":-)"

	 Then access your attributes like so (e.g. after calling ""$self =
	 SUPER->new();"" in your constructor method):

	     $self->[0][ATTRIB1] = 'value1';
	     $self->[0][ATTRIB2] = 'value2';
	     $self->[0][ATTRIB3] = 'value3';

	 Beware that if you put anything other than numbers or strings into
	 your attributes, the methods "clone()" and "copy()" might not work as
	 expected anymore!

	 Especially if your attributes contain references to other data
	 structures, only the references will be copied, but not the data
	 structures themselves.

	 This may not be what you want.

	 (You will have to override these two methods and write some of your
	 own if not.)

	 In order for the overloaded operators and the "shift_*()" auxiliary
	 functions from the "Date::Calc::Object" package to work properly (the
	 latter of which are heavily used in the "Date::Calendar[::Year]"
	 modules, for instance), the package name of your subclass (= the one
	 your objects will be blessed into) is REQUIRED to contain a "::".

	 Note that you should ONLY subclass "Date::Calc", NEVER
	 "Date::Calc::Object", since subclassing the latter is less efficient
	 (because "Date::Calc::Object" is just an empty class which inherits
	 from "Date::Calc" - subclassing "Date::Calc::Object" would thus just
	 introduce an additional name space layer to search during Perl's
	 runtime method binding process).

	 If you give your subclass a package name below/inside the "Date::"
	 namespace, you will also benefit from the fact that all error
	 messages produced by the "Date::Calc[::Object]" module (and also the
	 "Date::Calendar[::Year]" modules, by the way) will appear to have
	 originated from the place outside of all ""/^Date::/"" modules
	 (including yours) where one of the "Date::" modules was first called
	 - i.e., all errors are always blamed on the user, no matter how
	 deeply nested inside the "Date::" modules they occur, and do not
	 usually refer to places inside any of the "Date::" modules (this
	 assumes that there are no bugs in the "Date::" modules, and that all
	 errors are always the user's fault ":-)").

	 Moreover, your module's own error messages will behave in the same
	 way if you ""use Carp::Clan qw(^Date::);"" at the top of your module
	 and if you produce all error messages using "carp()" and "croak()"
	 (instead of "warn()" and "die()", respectively).

	    # Switch to summer time:
	    $now = Date::Calc->now();
	    if (($now ge [2000,3,26,2,0,0]) and
		($now lt [2000,3,26,3,0,0]))
		$now += [0,0,0,1,0,0];

	    use Date::Calc::Object qw(:all);


	    $date = 0;
	    while (!$date)
		print "Please enter the date of your birthday (day-month-year): ";
		$date = Date::Calc->new( Decode_Date_EU( scalar(<STDIN>) ) );
		if ($date)
		    $resp = 0;
		    while ($resp !~ /^\s*[YyNn]/)
			print "Your birthday is: $date\n";
			print "Is that correct? (yes/no) ";
			$resp = <STDIN>;
		    $date = 0 unless ($resp =~ /^\s*[Yy]/)
		    print "Unable to parse your birthday. Please try again.\n";

	    if ($date + [18,0,0] <= [Today()])
		{ print "Ok, you are over 18.\n"; }
		{ print "Sorry, you are under 18!\n"; }

       For more examples, see the "examples" subdirectory in this
       distribution, and their descriptions in the file "EXAMPLES.txt".

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

       This man page documents "Date::Calc::Object" version 6.3.

	 Steffen Beyer

       Copyright (c) 2000 - 2009 by Steffen Beyer. All rights reserved.

       This package is free software; you can use, modify and redistribute it
       under the same terms as Perl itself, i.e., at your option, under the
       terms either of the "Artistic License" or the "GNU General Public

       The C library at the core of the module "Date::Calc::XS" can, at your
       discretion, also be used, modified and redistributed under the terms of
       the "GNU Library General Public License".

       Please refer to the files "Artistic.txt", "GNU_GPL.txt" and
       "GNU_LGPL.txt" in the "license" subdirectory of this distribution for
       any details!

       This package is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of

       See the "GNU General Public License" for more details.

perl v5.10.1			  2009-10-31		 Date::Calc::Object(3)

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