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Date::Manip::Objects(3User Contributed Perl DocumentatiDate::Manip::Objects(3)

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

       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.

       Date::Manip consists of the following primary modules:

	   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

	   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.

	   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.

	   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

	   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.

	   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

	   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

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

       There are also many secondary modules including:


       None of these are intended to be used directly.

       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

       If you do need to work with multiple different configurations (such as
       parsing dates from multiple languages), please refer to the next

       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:


	   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.

       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_spa1 = new Date::Manip::Date;

	   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.

       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;

	       ... do some stuff


	       ... 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.

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

       Date::Manip	  - main module documentation

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

       Sullivan Beck (

perl v5.16.3			  2014-04-30	       Date::Manip::Objects(3)

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