NAME

       Date::Manip::Objects - A description of the various Date::Manip objects

SYNOPSIS

       The Date::Manip package consist of several modules, each of which perform a set of operations on a
       specific class of objects.  This document describes how the various modules work together.

DESCRIPTION

       Date::Manip consists of the following primary modules:

       Date::Manip::Obj
           The Date::Manip::Obj module is not intended for direct use. It is used as a base class for all other
           Date::Manip classes described below.

           The Date::Manip::Obj module contains some functions which are inherited by all these classes, so to
           understand all of the methods available to any of the classes below, you must include those
           documented in the Date::Manip::Obj class.

       Date::Manip::Base
           The Date::Manip::Base is used to perform basic operations including basic date operations, management
           of configuration options, handling the definitions used in different languages, etc.

           A Date::Manip::Base object does not, of itself, contain any date information. Instead, it contains
           configuration information which determines how the Date::Manip package performs date operations.  The
           configuration information is documented in the Date::Manip::Config document.

           The Date::Manip::Base object has one other property that is very important. When performing basic
           date operations, some intermediate results are cached in the object which leads to significant
           performance increases in later operations. As such, it is important to reuse the object as much as
           possible, rather than creating new Date::Manip::Base objects all the time.

           Much of the information in this document is related to this issue, and tells how to create various
           higher-level objects in order to get the most efficient reuse of this cached data.

           Because all other objects depend on a Date::Manip::Base object, a Date::Manip::Base object is
           embedded in all other objects, and the same Base object can be shared by any number of objects to
           achieve maximum performance.

       Date::Manip::TZ
           The Date::Manip::TZ module adds support for time zones. It is used to verify date and time zone
           information, convert dates from one time zone to another, and handle all daylight saving time
           transitions.

           Similar to the Date::Manip::Base object, a great deal of information is cached in the Date::Manip::TZ
           object. This includes lists of all time zones, offsets, and abbreviations for all time zones. It also
           includes more a more detailed description of every time zone that has actually been worked used.

           A Date::Manip::TZ object relies on a Date::Manip::Base object (and a Date::Manip::Base object is
           always embedded in a Date::Manip::TZ object).  All higher level objects (those listed next) depend on
           both a Date::Manip::Base and Date::Manip::TZ object, so a Date::Manip::TZ object is embedded in them.

           In order to achieve maximum performance, and minimize memory usage, a Date::Manip::TZ object can be
           shared by any number of higher level objects, and in fact, it is desirable to reuse the same
           Date::Manip::TZ object as often as possible.

       Date::Manip::Date
       Date::Manip::Delta
       Date::Manip::Recur
           These are the primary modules which are used to perform all high level date operations.

           The Date::Manip::Date class performs operations on dates (which includes a date, time, and time
           zone). The Date::Manip::Delta class performs operations with deltas (amounts of time). The
           Date::Manip::Recur class performs operations on recurring events.

           As mentioned above, each of these high level classes rely on both a Date::Manip::TZ object and a
           Date::Manip::Base object, so a Date::Manip::TZ object is embedded in each one (and the
           Date::Manip::TZ object has a Date::Manip::Base object embedded in it).

           A Date::Manip::Date object contains a single date, so in order to work with multiple dates, multiple
           Date::Manip::Date objects will need to be created. In order to make the most effective use of cached
           information in the Date::Manip::Base object, the same Date::Manip::TZ object can be embedded in each
           of the higher level objects.

           The same goes for multiple Date::Manip::Delta and Date::Manip::Recur objects.

       There are also many secondary modules including:

          Date::Manip::TZ_Base
          Date::Manip::TZdata
          Date::Manip::Zones
          Date::Manip::Lang::*
          Date::Manip::TZ::*
          Date::Manip::Offset::*

       None of these are intended to be used directly.

WORKING WITH DATE::MANIP OBJECTS (SINGLE CONFIGURATION)

       By far the most common usage of Date::Manip involves setting a single local time zone, parsing dates in a
       single language, and having all other configuration parameters set to a single value that doesn't change
       over the course of the program.

       Whenever this is the case, you can use the methods listed in this section to create any number of
       Date::Manip objects. It will automatically optimize the use of cached data to get the best performance.

       If you do need to work with multiple different configurations (such as parsing dates from multiple
       languages), please refer to the next section "WORKING WITH DATE::MANIP OBJECTS (MULTIPLE CONFIGURATION)".

       Working with high level objects
           The most common situation is one where you will need to use one or more high level objects (Date,
           Delta, or Recur objects). In addition, you may want to use the lower level (Base or TZ) objects.

           The first thing you should do is to create your initial object. Create the highest level object you
           will be using. For example if you will be working with dates, create the first date object with:

              $date = new Date::Manip::Date;

           The next step is to set the configuration values. Use the config method to do this:

              $date->config(ARGS);

           Although you can call the config method later, it is strongly suggested that the configuration be set
           soon after the initial object is created and not altered later. Every time you alter the
           configuration, some of the cached data is cleared, so for optimal performance, you don't want to
           alter the configuration if possible.

           Additional high-level objects can be created using the calls:

              $date2 = $date->new_date();
              $delta = $date->new_delta();
              $recur = $date->new_recur();

           To access the embedded Date::Manip::TZ and Date::Manip::Base objects, use the calls:

              $tz    = $date->tz();
              $base  = $date->base();

       Working with low level objects only
           If you will only be working with low level objects, create them with one of the calls:

              $tz    = new Date::Manip::TZ;
              $base  = new Date::Manip::Base;

           To get the base object embedded in a Date::Manip::TZ object, use:

              $base  = $tz->base();

       For a more complete description of the methods used here, refer to the Date::Manip::Obj document.

WORKING WITH DATE::MANIP OBJECTS (MULTIPLE CONFIGURATION)

       Occasionally, it may be useful to have multiple sets of configurations.  In order to do this, multiple
       Date::Manip::Base objects must be created (each with their own set of configuration options), and then
       new Date::Manip objects are created with the appropriate Date::Manip::Base object embedded in them.

       Possible reasons include:

       Parsing multiple languages
           A Date::Manip::Base object includes information about a single language. If you need to parse dates
           from two (or more) languages, a Date::Manip::Base object needs to be created for each one. This could
           be done as:

              $date_eng1 = new Date::Manip::Date;
              $date_eng1->config("language","English");

              $date_spa1 = new Date::Manip::Date;
              $date_spa1->config("language","Spanish");

           Any additional Date::Manip objects created from the first will work with English. Additional objects
           created from the second will work in Spanish.

       Business modes for different countries and/or businesses
           If you are doing business mode calculations (see Date::Manip::Calc) for two different businesses
           which have different holiday lists, work weeks, or business days, you can create different objects
           which read different config files (see Date::Manip::Config) with the appropriate description of each.

       The primary issue when dealing with multiple configurations is that it is necessary for the programmer to
       manually keep track of which Date::Manip objects work with each configuration. For example, refer to the
       following lines:

          $date1 = new Date::Manip::Date [$opt1,$val1];
          $date2 = new Date::Manip::Date $date1, [$opt2,$val2];
          $date3 = new Date::Manip::Date $date1;
          $date4 = new Date::Manip::Date $date2;

       The first line creates 3 objects: a Date::Manip::Base object, a Date::Manip::TZ object, and a
       Date::Manip::Date object). The Date::Manip::Base object has the configuration set to contain the value(s)
       passed in as the final list reference argument.

       The second line creates 3 new objects (a second Date::Manip::Base object, a second Date::Manip::TZ
       object, and a second Date::Manip::Date object). Since a list reference containing config variables is
       passed in, a new Date::Manip::Base object is created, rather than reusing the first one. The second
       Date::Manip::Base object contains all the config from the first, as well as the config variables passed
       in in the list reference argument.

       The third line creates another Date::Manip::Date object which uses the first Date::Manip::Base and
       Date::Manip::TZ objects embedded in it.

       The fourth line creates another Date::Manip::Date object which uses the second Date::Manip::Base and
       Date::Manip::TZ objects embedded in it.

       Most of the time there will only be one set of configuration options used, so this complexity is really
       for a very special, and not widely used, bit of functionality.

WORKING WITH DATE::MANIP OBJECTS (ADDITIONAL NOTES)

       object reuse
           In order to create additional Date::Manip objects, a previously created object should be passed in as
           the first argument. This will allow the same Base object to be embedded in both in order to maximize
           data reuse of the cached intermediate results, and will result in much better performance. For
           example:

              $date1 = new Date::Manip::Date;
              $date2 = new Date::Manip::Date $date1;

           This is important for two reasons. First is memory usage. The Date::Manip::Base object is quite
           large. It stores a large number of precompile regular expressions for language parsing, and as date
           operations are done, intermediate results are cached which can be reused later to improve
           performance. The Date::Manip::TZ object is even larger and contains information about all known time
           zones indexed several different ways (by offset, by abbreviation, etc.). As time zones are actually
           used, a description of all of the time change rules are loaded and added to this object.

           Since these objects are so large, it is important to reuse them, rather than to create lots of copies
           of them. It should be noted that because these objects are embedded in each of the high level object
           (Date::Manip::Date for example), it makes these objects appear quite large.

           The second reason to reuse Date::Manip::Base objects is performance. Since intermediate results are
           cached there, many date operations only need to be done once and then they can be reused any number
           of times. In essence, this is doing the same function as the Memoize module, but in a more efficient
           manner. Memoize caches results for function calls. For Date::Manip, this would often work, but if you
           change a config variable, the return value may change, so Memoize could cause things to break. In
           addition, Memoize caches primarily at the function level, but Date::Manip stores caches intermediate
           results wherever performance increase is seen. Every time I consider caching a result, I run a test
           to see if it increases performance. If it doesn't, or it doesn't make a significant impact, I don't
           cache it.

           Because the caching is quite finely tuned, it's much more efficient than using a generic (though
           useful) tool such as Memoize.

       configuration changes
           As a general rule, you should only pass in configuration options when the first object is created. In
           other words, the following behavior is discouraged:

               $date = new Date::Manip::Date;
               $date->config(@opts);

               ... do some stuff

               $date->config(@opts);

               ... do some other stuff

           Because some of the cached results are configuration specific, when a configuration change is made,
           some of the cached data must be discarded necessitating those results to be recalculated.

           If you really need to change configuration in the middle of execution, it is certainly allowed of
           course, but if you can define the configuration once immediately after the object is first created,
           and then leave the configuration alone, performance will be optimized.

BUGS AND QUESTIONS

       Please refer to the Date::Manip::Problems documentation for information on submitting bug reports or
       questions to the author.

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@cpan.org)