Date::Manip::Objects(3User Contributed Perl DocumentaDate::Manip::Objects(3pm)
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)
perl v5.36.0 2023-03-05 Date::Manip::Objects(3pm)
Generated by dwww version 1.15 on Wed Jun 26 05:12:44 CEST 2024.