This and other RFCs are available on the web at http://dev.perl.org/rfc/ =head1 TITLE Replace localtime() and gmtime() with date() and utcdate() =head1 VERSION Maintainer: Nathan Wiger <[EMAIL PROTECTED]> Date: 05 Aug 2000 Last Modified: 15 Sep 2000 Mailing List: [EMAIL PROTECTED] Number: 48 Version: 3 Status: Developing Requires: RFC 21, RFC 159 =head1 CHANGES 1. Renamed UTC date function to utcdate() and clarified use of UTC, not GMT. While two separate functions are less desireable than one, no easily-usable methods for computing timezones by name ('US/Pacific') have been produced. Suggestions welcome. 2. Changed return value of ->setformat member function to return the old format string, instead of the date. 3. Removed several values from the list context, instead moving them to the hash context and object contexts only. Also removed duplicate names in favor of English words (i.e., changed "->mon" to "->month"). 4. Added better polymorphic overloading via methods from RFC 159: True Polymorphic Objects. Also added more basic contexts via RFC 21 on want(). =head1 ABSTRACT Currently, Perl uses the C library C<localtime()> and C<gmtime()> functions for date access. However, because of many problems, these should be replaced with two new functions, C<date()> and C<utcdate()> that will be called as follows: $object = date; # object with accessor functions (new) print "$object"; # scalar ctime date, same as current @array = date; # list of date/time values (new order) %hash = date; # hash of date/time values (new) The new C<date()> function will return time adjusted for the local timezone. The C<utcdate()> function will return time in UTC. In a scalar context, an object is always returned. This object is then converted to a string on-demand via RFC 159: True Polymorphic Objects. =head1 DESCRIPTION =head2 Overview In the past, Perl has provided access to date and time information through the C library C<localtime()> and C<gmtime()> functions. Unfortunately, these functions have several "really bad things" about them: 1. some values are 0-indexed while others are 1-indexed 2. they return massive lists as their only interface 3. minute and second values aren't 0-padded 4. the year has to have 1900 added to it to be correct. While some of these are perhaps understandable, that last one just plain doesn't make I<any> sense. :-) With Perl 6 we have the chance to fix this. While some have suggested merely changing what C<localtime()> and C<gmtime()> return, this is a bad idea because: 1. Many Perl scripts already use it 2. Many C programmers are familiar with its stupidity As such, we should replace these functions with versions that work the way that we want them to. The new names will indicate that these are "not the same old time functions", and that you'd better read the docs. =head2 Proposed Syntax The new syntax of C<date()> and C<utcdate> is proposed as: $|@|%return = date [ $time ], [ $format ]; If C<$time> is not specified, then the current return value from C<time()> is used (just like C<localtime()>). The optional C<$format> affects the format of the date returned. By default, a ctime-formatted string is used, like C<localtime>. However, any POSIX-compatible format can be passed in, in which case the date returned in a scalar context is formatted accordingly. I<Actually>, what it does is call the object function C<setformat()> with the format, which in turn determines what calls to the C<date()> object member function look like. Since the C<date()> member function is what is output when the date object is stringified, this is how the scalar date appears to change. See below. The C<$format> specifier is the same one used in C<POSIX strftime()>, allowing complete date formatting with having to import the C<POSIX> module. Depending on the context within which C<date()> is called, many different things are returned: # Get some various local date stuff $object = date; # scalar ctime date, same as now $object = date time, '%m/%d/%Y'; # set date MM/DD/YYYY format $object = date $time; # relative to time $time print "$object"; # scalar date string per format @array = date; # array of date/time values %hash = date; # hash of values # Access UTC information $object = utcdate time, '%H:%M'; # return time in UTC =head2 Return Values The return values are dependent on the context within which C<date()> is called. For all contexts, the following are the values and their ranges: $hour = 0 .. 23 $min = 00 .. 59 # 0-padded $sec = 00 .. 59 # 0-padded $fsec = 0 .. 1 # fractional seconds per hw clock $month = 1 .. 12 # hooray! $day = 1 .. 31 $year = 1 .. 9999 # 4-digit! $wday = 1 .. 7 # 1 == *Monday*, POSIX-compliant $yday = 1 .. 366 $isdst = 1 or undef; # daylight savings? $isgmt = 1 or undef; # is GMT? $tz = [depends on your system, this "eats people"] For those who are concerned about $wday not being 0-indexed, please see below under the object methods. Remember you can always use formats to return what you want as well. =head3 STRING Context In a C<STRING> (not scalar) context, a single ctime-formatted date string is returned, consistent with the current usage of C<localtime()>. If the optional C<$format> is included, this format is used to change the string accordingly. In order to emulate a string, a call is made to the date object's builtin C<STRING> function, which prints out a date string. This is per RFC 159: True Polymorphic Objects. =head3 LIST, ARRAY, and ARRAYREF Contexts A list of date/time values is returned. The ordering and format of these values has been radically changed to reflect what most of us probably view as "ordinary": ($year, $month, $day, $hour, $min, $sec, $tz) = date; You'll note that many elements, such as $isdst, $wday, and $yday have been dropped from the list return context. This is to encourage the use of more sane contexts, such as object and hash/hashrefs for complex operations. This ordering follows the predictable pattern of being in increasing granularity and so should be easy to remember. Just think of a computer-esque decending timestamp: 2000/11/4 12:03:09 Note that the month, day, and year are not 0-padded. If you want a padded date, perhaps as a file backup suffix, you'll have to say: $backup_suffix = date time, '%Y%m%d%H%M%S'; Which would return something like "20001104120309" (actually, it would return an object with the appropriate default format so that, when stringified, it would yield the above result). These same values can be retrieved when referred to as an arrayref, so these two: $month = (date)[1]; $month = date->[1]; Have the same effect. Now, of course, if you want specific values you should be using... =head3 HASH and HASHREF Contexts A hash of values is returned. These are named the same as the variables above. So, %date = date; Would return a hash with these values (assuming the same date shown above): $date{year} = 2000; $date{month} = 11; $date{day} = 4; $date{hour} = 12; $date{min} = 03; $date{sec} = 09; $date{fsec} = 0.4291; # up to hw resolution $date{wday} = 2; $date{yday} = 331; $date{tz} = 'PST'; # or maybe 'US/Pacific', or ... $date{isdst} = undef; These same values will be available via a HASHREF, so again these: $month = ${(date)}{month}; $month = date->{month}; Will work the same (at least, I think that first one's right per RFC 21)... =head3 SCALAR Context In an C<SCALAR> context, an object is returned. This is somewhat adapted from C<Time::Object> and Larry's own comments, but with several key differences. The ones noted with * are incompatible with C<Time::Object> $t = date; # create date object "$t" # calls $t->STRING, same as $t->date $t++ # calls $t->NUMBER, same as $t->time $t->year $t->month # * $t->day # * $t->hour $t->min $t->sec $t->fsec # fractional seconds $t->fsecres # fsec resolution (num of digits for hw) $t->wday # * $t->yday $t->isdst $t->tz $t->tzoffset # timezone offset in seconds ($t->tzsec?) $t->time # number of seconds since the epoch, so it # contains what time() was when you called # date() These functions are object-specific: $t->date # Tue Feb 29 01:23:45 2000 (depending on # default format set by $t->setformat) $t->date(FORMAT) # Return a temporarily-modified date, # without affecting the default format. $t->setformat(FORMAT) # Set default format which determines what # calls to $t->date (stringified $t) look like # This is called on object creation These functions are separate for an important reason: print $t->date('%H:%M'); # prints out hours and minutes print "$t"; # without touching default format $oldfmt = $t->setformat('%Y'); # sets POSIX fmt string print "$t"; # which affects the default format The C<set> prefix was explicitly added to make it obvious this sets something (rather than just formatting the date like strftime). Many functions were deemed of dubious quality/excessive bloat and were all removed from the RFC. Note that you can get to any extra data by calling $t->date with the correct format. So, print $t->date('%w'); Will give you the weekday numbered starting with 0 == Sunday. =head2 Date Arithmetic You'll note that simple date arithmetic is available via polymorphic overloading in numeric contexts. For example: $t1 = date; $t2 = date; $diff = $t2 - $t1; # calls ->NUMBER (->time) on both The result will simply be the difference in seconds between the two, in simple scalar form (i.e., "15"). The result is designed to be the same as if you had created $t1 and $t2 based on the output of time(), without requiring you to put extra calls in your code. To simply increment the date by one second each loop, do: $d = date; while (stuff()) { $d++; } This gives the basis from which more complex date arithmetic can be derived, which should be in a module. =head1 IMPLEMENTATION Slash and burn C<localtime()> and C<gmtime()>. Actually, we should probably move them to C<Time::Local> or some other place and keep them available, since some people like pain. Nonetheless, C<localtime()> and C<gmtime()> SHOULD BE REMOVED FROM CORE and placed in a module. Perl 6 should support ONE date/time specification natively. Extensive date calculations, including reverse date calculations, should be left to an external module. I am currently working on a Perl 5 prototype and will announce it to the list when it is completed. =head1 ACKNOWLEDGEMENTS Jonathan Scott Duff, Tim Jenness, Johan Vromans, Buddha Buck, and lots of other members of perl6-language for great feedback. Russ Allbery and John Tobey for suggesting parts to slice-and-dice. =head1 REFERENCES Larry Wall's post of 8 Jan 2000 on deprecating localtime: http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2000-01/msg00241.html RFC 159: True Polymorphic Objects RFC 21: Replace wantarray() with a generic want() function RFC 37: Positional Return Lists Considered Harmful Matt Sergeant's great Time::Object CPAN module http://www.jach.hawaii.edu/JACpublic/stardocs/sun67.htx/node217.html http://tycho.usno.navy.mil/systime.html
