Date::Manip::Problems - phpMan

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NAME
Date::Manip::Problems - problems and bugs

KNOWN PROBLEMS
The following are not bugs in Date::Manip, but they may give some people
problems.

Unable to determine Time Zone
If you ever get the message that Date::Manip was unable to determine
the timezone, you need to provide that information to your script.
Please refer to the Date::Manip::TZ documentation for a discussion
of this problem.

Calculations appear to be off by an hour
Due to daylight saving time (especially the spring change where the
time typically moves forward from 02:00 to 03:00), any date
calculation which would intuitively report a time in that range will
also move forward (or backward as the case may be).

*NOTE* This should be less of a problem since 6.30 with the addition
of semi-exact deltas.

Missing date formats
Due to the large number of date formats that Date::Manip CAN
process, people often assume that other formats that they want to
use should work as well, and when they don't, it comes as a
surprise.

With the much improved parsing of 6.00, many formats can be added
easily, though unless they are of general use, I'll probably suggest
that you use parse_format instead.

There is a class of formats that I do not plan to add however.

I have frequently been asked to add formats such as "the 15th of
last month", or "Monday of next week". I do not intend to add these
date formats to Date::Manip, but since I have received the request
several times, I decided to include my reasoning here.

Date::Manip can parse pretty much any static date format that I
could think of or find reference to. Dates such as "today", "Jan
12", or "2001-01-01" are all understood.

These are fairly limited however. Many very common date formats are
best thought of as a date plus a modification. For example,
"yesterday" is actually determined internally as "today" plus a
modification of "- 1 day". "2nd Sunday in June" is determined as
"June 1" modified to the 2nd Sunday.

As these types of formats were added over time, I quickly realized
that the number of possible date plus modification formats was huge.
The number of combinations has caused the parsing in Date::Manip to
be quite complex, and adding new formats occasionally causes
unexpected conflicts with other formats.

The first time I received a request similar to "the 15th of last
month", I intended to add it, but as I analyzed it to see what
changes needed to be made to support it, I realized that this needed
to be expressed as a date plus TWO modifications. In other words,
today modified to last month modified to the 15th day of the month.

As bad as date plus modification formats are, a date plus TWO
modifications would be exponentially worse. On realizing that, I
decided that Date::Manip will not support this type of format.

Although I apologize for the inconvenience, I do not intend to
change my position on this.

Date::Manip is slow
Date::Manip is one of the slower Date/Time modules due to the fact
that it is huge and written entirely in perl. I have done a lot of
work optimizing it since 6.xx came out, and additional work is
planned, but even at it's best, it will probably be slower than
other modules.

Some things that will definitely help:

Date::Manip 5.xx was very slow. A lot of work went into speeding it
up as I rewrote it for the 6.xx release, and it should be noted that
initial tests show version 6.xx to be around twice as fast as 5.xx.
There is one notable exception to this speedup. If you use
Date::Manip to parse dates from a wide variety of timezones, 6.xx
will be significantly slower than 5.xx. The reason for this is that
each time a new timezone is accessed, 6.xx does quite a bit of work
to initialize it. 5.xx does not have this overhead, so it can parse
dates from any number of timezones without a speed penalty. However,
5.xx does NOT handle timezones correctly, so many of the dates will
be incorrect. If timezones are important to you, there is no way to
use 5.xx and get accurate results.

If you only parse dates from a single timezone (which is more often
what you are doing), 6.xx is significantly faster than 5.xx.

ISO-8601 dates are parsed first and fastest. If you have the
flexibility to define the date format, use ISO-8601 formats whenever
possible.

Avoid parsing dates that are referenced against the current time (in
2 days, today at noon, etc.). These take a lot longer to parse.

Business date calculations are extremely slow. You should consider
alternatives if possible (i.e. doing the calculation in exact mode
and then multiplying by 5/7). Who needs a business date more
accurate than "6 to 8 weeks" anyway, right :-)

Memory leak
There is a known memory leak in perl related to named regexp
captures that directly affects Date::Manip . The leak is in all
versions of perl up to (and including) the following versions:

5.10.1
5.12.5
5.14.3
5.15.5

The bug has been fixed in:

5.15.6
5.16.0

If a maintenance release is done for any of the other releases
(5.10, 5.12, 5.14), that includes the patch, I'll update this
section to include that information.

Date::Manip 5.xx is not susceptible, so using it may be a feasible
workaround, but if you need accurate timezone handling, this isn't
possible.

Simple tests estimate the leak to be about 3 MB per 10,000 dates
parsed, so unless you're parsing hundreds of thousands, or millions
of dates, the leak probably won't be a problem on systems with
moderate amounts of memory. And if you're parsing that many dates,
the relatively slow Date::Manip may not be the correct module for
you to use anyway.

Dmake error on strawberry perl
Users of Strawberry perl on windows may encounter an error similar
to the following:

dmake: makefile: line 3016: Error: -- Input line too long, increase MAXLINELENGTH

This is a known problem with some versions of strawberry perl, and I
can't fix it in Date::Manip. If you encounter this problem, you can
install the package manually using the commands:

c:> cpan
cpan> look Date::Manip::Date
> perl Makefile.PL
> dmake MAXLINELENGTH=300000 make
> dmake MAXLINELENGTH=300000 make test
> dmake MAXLINELENGTH=300000 make install

You can find more details here:

http://www.nntp.perl.org/group/perl.win32.vanilla/2011/02/msg287.html

Using functions/methods which are not supported
There have been a handful of incidents of people using a function
from Date::Manip which were not documented in the manual.

Date::Manip consists of a large number of user functions which are
documented in the manual. These are designed to be used by other
programmers, and I will not make any backwards incompatible changes
in them unless there is a very compelling reason to do so, and in
that case, the change will be clearly documented in the
Date::Manip::Changes6 documentation for this module.

Date::Manip also includes a large number of functions which are NOT
documented. These are for internal use only. Please do not use them!
I can (and do) change their functionality, and even their name,
without notice, and without apology! Some of these internal
functions even have test scripts, but that is not a guarantee that
they will not change, nor is any support implied. I simply like to
run regression tests on as much of Date::Manip as possible.

As of the most recent versions of Date::Manip, all internal
functions have names that begin with an underscore (_). If you
choose to use them directly, it is quite possible that new versions
of Date::Manip will cause your programs to break due to a change in
how those functions work.

Any changes to internal functions will not be documented, and will
not be regarded by me as a backwards incompatibility. Nor will I (as
was requested in one instance) revert to a previous version of the
internal function.

If you feel that an internal function is of more general use, feel
free to contact me with an argument of why it should be "promoted".
I welcome suggestions and will definitely consider any such request.

RCS Control
If you try to put Date::Manip under RCS control, you are going to
have problems. Apparently, RCS replaces strings of the form
"$Date...$" with the current date. This form occurs all over in
Date::Manip. To prevent the RCS keyword expansion, checkout files
using:

co -ko

Since very few people will ever have a desire to do this (and I
don't use RCS), I have not worried about it, and I do not intend to
try to workaround this problem.

KNOWN COMPLAINTS
Date::Manip 6.xx has gotten some complaints (far more than 5.xx if the
truth be told), so I'd like to address a couple of them here. Perhaps an
understanding of why some of the changes were made will allay some of
the complaints. If not, people are always welcome to stick with the 5.xx
release. I will continue to support the 5.xx releases for a couple years
(though I do NOT plan to add functionality to it).

These complaints come both from both the CPAN ratings site:

http://cpanratings.perl.org/dist/Date-Manip

and from personal email.

Requires perl 5.10
The single most controversial change made in 6.00 is that it now
required perl 5.10.0 or higher. Most of the negative feedback I've
received is due to this.

In the past, I've avoided using new features of perl in order to
allow Date::Manip to run on older versions of perl. Prior to perl
5.10, none of the new features would have had a major impact on how
Date::Manip was written so this practice was justified. That all
changed with the release of perl 5.10.

One of the aspects of Date::Manip that has received the most
positive response is the ability to parse almost every conceivable
date format. Unfortunately, as I've added formats, the parsing
routine became more and more complicated, and maintaining it was one
of the least enjoyable aspect in maintaining Date::Manip . In fact,
for several years I'd been extremely reluctant to add new formats
due to the fact that too often, adding a new format broke other
formats.

As I was rewriting Date::Manip, I was looking for ways to improve
the parsing and to make maintaining it easier. Perl 5.10 provides
the feature "named capture buffers". Named capture buffers not only
improves the ease of maintaining the complex regular expressions
used by Date::Manip, it makes it dramatically easier to add
additional formats in a way that is much less likely to interfere
with other formats. The parsing in 6.00 is so much more robust,
extensible, and flexible, that it will make parser maintenance
possible for many years to come at a fraction of the effort and
risk.

It was too much to turn down. Hopefully, since 5.10 has been out for
some time now, this will not prohibit too many people from using the
new version of Date::Manip. I realize that there are many people out
there using older versions of perl who do not have the option of
upgrading perl. The decision to use 5.10 wasn't made lightly... but
I don't regret making it. I apologize to users who, as a result,
cannot use 6.00 . Hopefully in the future you'll be able to benefit
from the improvements in 6.00.

One complaint I've received is that this in some way makes
Date::Manip backwards incompatible, but this is not an accurate
complaint. Version 6.xx DOES include some backwards
incompatibilities (and these are covered in the
Date::Manip::Migration5to6 document), however in almost all cases,
these incompatibilities are with infrequently used features, or
workarounds are in place to allow deprecated features to continue
functioning for some period of time.

Though I have no data to confirm this, I suspect that 90% or more of
all scripts which were written with Date::Manip 5.xx will continue
to work unmodified with 6.xx (of course, you should still refer to
the migration document to see what features are deprecated or
changed to make sure that you don't need to modify your script so
that it will continue to work in the future). Even with scripts that
need to be changed, the changes should be trivial.

So, Date::Manip 6.xx is almost entirely backward compatible with
5.xx (to the extent that you would expect any major version release
to be compatible with a previous major version).

The change is only in the requirements necessary to get Date::Manip
6.xx to run.

Obviously, it's not reasonable to say that Date::Manip should never
be allowed to switch minimum perl versions. At some point, you have
to let go of an old version if you want to make use of the features
of the newer version. The question is, did I jump to 5.10 too fast?

The negative ratings I see in the CPAN ratings complain that I no
longer support perl 5.6 and perl 5.8.

With respect to 5.6, perl 5.6 was released in March of 2000 (that's
before Windows XP which was released in 2001). Date::Manip 6.00 was
released at the end of 2009. To be honest, I don't really feel much
sympathy for this complaint. Software that is 9 years old is
ANCIENT. People may choose to use it... but please don't complain
when new software comes out that doesn't support it.

The argument for perl 5.8 is much more compelling. Although 5.8 was
released well before Date::Manip 6.00 (July of 2002), there were no
major perl releases until 5.10 came out in December of 2007, so 5.8
was state-of-the art as little as 2 years prior to the release of
Date::Manip 6.xx.

I agree completely with the argument that abandoning 5.8 only 2
years after it was the current version is too soon. For that reason,
I continued to support the Date::Manip 5.xx releases for several
years. As of December 2012 (5 years after the release of perl 5.10),
the 5.xx release is no longer supported (in that I will not patch it
or provide support for it's use). However, it is still bundled into
the Date::Manip distribution so it can still be used. I do not have
any plans for removing it, though I may do so at some point.

Too many modules
One minor complaint is that there are too many files. One person
specifically objects to the fact that there are over 470 modules
covering non-minute offsets. This complaint is (IMO) silly.

Date::Manip supports ALL historical time zones, including those with
non-minute offsets, and so there will be information for those time
zones, even though they are not currently in use.

I could of course store all of the information in one big module,
but that means that you have to load all of that data every time you
use Date::Manip, and I find that to be a very poor solution.
Instead, storing the information in a per-time zone and per-offset
manner dramatically decreases the amount of data that has to be
loaded.

While it is true that Date::Manip includes over 900 modules for all
of the time zone information, most implementations of time zone
handling also choose to break up the data into a large number of
files.

My linux distribution (openSuSE 11.2 at the time of writing this)
uses the standard zoneinfo database, and at this point, there are
over 1700 files included in /usr/share/zoneinfo (though it does
appear that there is some duplication of information). Current
versions of RedHat also use over 1700 files, so Date::Manip isn't
treating the time zone data in a new or unreasonable way.

Objects are large
One complaint that was put on the CPAN ratings site was that the OO
interface is "a dud" due to the size of it's objects. The complaint
is that a Date::Manip::Date object is 115K while it should
(according to the complaint) only require that you need to save the
seconds from the epoch, zone, and a couple other pieces of
information, all of which could probably be stored in 100 bytes or
less.

This complaint is not accurate, and comes from a misunderstanding of
the objects used by Date::Manip.

Date::Manip is very configurable, and contains a great deal of
information which could theoretically be calculated on the fly, but
which would greatly reduce it's performance. Instead, in the
interest of improving performance, the data is cached, and since the
data is virtually all potentially object specific, it has to be
somehow linked to the object.

For example, Date::Manip allows you to parse dates in several
languages. Each language has a large number of regular expressions
which are used to do the actual parsing. Instead of recreating these
regular expressions each time they are needed, they are created once
and stored in an object (specifically, a Date::Manip::Base object).
The size of the Date::Manip::Base object is almost 15K (due
primarily to the regular expressions used in parsing dates in the
selected language).

Similarly, a description of the time zones are stored in a second
object (a Date::Manip::TZ object). The size of the Date::Manip::TZ
object starts at 100K. That may seem excessive, but you have to
remember that there are almost 500 time zones, and they have to be
indexed by name, alias, abbreviation, and offset. In addition,
critical dates (dates where the offset from GMT change such as
during a daylight saving time change) along with information such as
offsets, abbreviation, etc., are all cached in order to improve
performance. By the time you do this, it does take a fair bit of
space. It should also be noted that the full description of each
timezone is only stored in the object when the timezone is actually
used, so if you use a lot of timezones, this object will grow slowly
as new timezones are used.

The size of the actual Date::Manip::Date object is a little over 300
bytes. However, each includes a pointer to a Date::Manip::Base and a
Date::Manip::TZ object (and due to how the object was being looked
at in the complaint, they were reporting the size of all three
objects, NOT just the Date::Manip::Date object).

Both the Date::Manip::Base and Date::Manip::TZ objects are reused by
any number of Date::Manip::Date objects. They can almost be thought
of as global data, except that they are accessible in the standard
OO manner, and you are allowed to modify them on a per-object basis
which WILL mean that you have to store more data. If you work with
multiple configurations (see Date::Manip::Config), you'll need
multiple Base and TZ objects. However, most of the time you will not
need to do this.

The actual Date::Manip::Date object is a bit larger than suggested
in the complaint, but it should be noted that Date::Manip actually
stores the dates in a number of different formats (a string of the
form YYYYMMDDHH:MN:SS and a list [YYYY,MM,DD,HH,MN,SS] in the time
zone it was parsed in, the local time zone (if different) and GMT.
By caching this information as it is used, it has a huge impact on
the performance.

So, Date::Manip in typical usage consists of one 100K
Date::Manip::TZ object, one 15K Date::Manip::Base objects, and any
number of small 300 byte Date::Manip::Date objects.
Date::Manip::Delta objects are even smaller. Date::Manip::Recur
objects are also small, but they contain any number of Date objects
in them.

I am certainly open to suggestions as to how I can improve the OO
interface... but I don't believe it is a dud. While I'm not an
expert at OO programming, I believe that I followed pretty standard
and accepted procedures for accessing the data.

Please refer to the Date::Manip::Objects document for more
information.

Date::Manip has an inconsistent interface
I've gotten a few complaints that the interface to Date::Manip is
inconsistent... and I agree (at least when referring to the
functional interfaces).

Date::Manip was originally written in an unplanned way... as a
need/want came up, it was extended. That's not the way to write a
major package of course, but it wasn't expected to be a major
package at the start.

As it became more and more widely used, I too wished for a more
consistent interface, but I did not want to break backward
compatibility for everyone using it.

When 6.xx was written, I spent a good deal of time trying to make a
very standard OO interface, so I do not believe that this complaint
can be applied to the OO interface (though I'm interested in
suggestions for improving it of course).

As far as the functional interface goes, I'll continue to support it
in a backward compatible (and therefore inconsistent) form. I'd
encourage the use of the OO interface whenever possible.

BUGS AND QUESTIONS
If you find a bug in Date::Manip, there are three ways to send it to me.
In order of preference, they are:

GitHub
You can submit it as an issue on GitHub. This can be done at the
following URL:

<https://github.com/SBECK-github/Date-Manip>

This is the preferred method. Please submit problems requests as
GitHub issues if at all possible.

Direct email
You are welcome to send it directly to me by email. The email
address to use is: sbeck AT cpan.org.

Please note that because cpan.org addresses are published, they are
used by a lot of spammers and phishers. Please include the name of
the perl module in the subject line of ALL messages sent to my
cpan.org address or it will likely be missed.

CPAN Bug Tracking
You can submit it using the CPAN tracking too. This can be done at
the following URL:

<http://rt.cpan.org/Public/Dist/Display.html?Name=Date-Manip>

There was discussion of halting this service a while back (though it
continues to function), so only use this as a last resort.

Please do not use other means to report bugs (such as forums for a
specific OS or Linux distribution) as it is impossible for me to keep up
with all of them.

When filing a bug report, please include the following information:

Date::Manip version
Please include the version of Date::Manip you are using. You can get
this by using the script:

use Date::Manip;
print DateManipVersion(1),"\n";

use Date::Manip::Date;
$obj = new Date::Manip::Date;
print $obj->version(1),"\n";

Perl information
Please include the output from "perl -V"

If you have a problem using Date::Manip that perhaps isn't a bug (can't
figure out the syntax, etc.), you're in the right place. Start by
reading the main Date::Manip documentation, and the other documents that
apply to whatever you are trying to do. If this still doesn't answer
your question, mail me directly.

I would ask that you be reasonably familiar with the documentation
BEFORE you choose to do this. Date::Manip is a hobby, and I simply do
not have time to respond to hundreds of questions which are already
answered in this manual.

If you find any problems with the documentation (errors, typos, or items
that are not clear), please send them to me. I welcome any suggestions
that will allow me to improve the documentation.

KNOWN BUGS
None known.

SEE ALSO
Date::Manip - main module documentation

LICENSE
This script is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.

AUTHOR
Sullivan Beck (sbeck AT cpan.org)