= ThirdBase: A Fast and Easy Date/DateTime Class for Ruby

ThirdBase differs from Ruby's standard Date/DateTime class in the
following ways:

- ThirdBase is roughly 2-12 times faster depending on usage
- ThirdBase has a lower memory footprint
- ThirdBase supports pluggable parsers
- ThirdBase doesn't depend on Ruby's Rational class
- ThirdBase always uses the gregorian calendar

== Background

The Ruby standard Date class tries to be all things to all people.
While it does a decent job, it's slow enough to be the bottleneck in
some applications.  If we decide not to care about the Date of
Calendar Reform and the fact that the Astronomical Julian Date differs
from the Julian Date, much of the complexity of Ruby's standard
Date/DateTime class can be removed, and there can be significant
improvements in speed.

== Resources

* {RDoc}[http://third-base.rubyforge.org]
* {Source code}[http://github.com/jeremyevans/third_base]
* {Bug tracking}[http://rubyforge.org/projects/third-base/]

To check out the source code:

  git clone git://github.com/jeremyevans/third_base.git

== Installation

  sudo gem install third_base

== Usage and Compatibility

There are three ways that ThirdBase can be used:

=== Alongside the standard Date/DateTime class

Usage:

  require 'third_base'

If you just require it, you can use ThirdBase::Date and
ThirdBase::DateTime alongside the standard Date and DateTime classes.
This ensures compatibility with all existing software, but doesn't
provide any performance increase to any class not explicitly using
ThirdBase.

=== Replace Date and DateTime with ThirdBase's

Usage:

  require 'third_base'
  include ThirdBase

This is the least compatible method.  It may work for some
applications but will break most, because if they use "require
'date'", they will get a superclass mismatch.  Also ThirdBase::Date is
not completely API compatible with the standard Date class, so it
could break depending on how the application used Date.

If you aren't using any libraries that use ruby's standard Date class,
this is an easy way to be able to use Date and DateTime to refer to
ThirdBase's versions instead of Ruby's standard versions.

Note that rubygems indirectly uses the standard Date class, so if you
want to do this, you'll have to unpack the gem and put it in the
$LOAD_PATH manually.

One case in which this pattern is useful is if you want to use
ThirdBase within your libraries as the date class, but with other
libaries that use the standard version as the date class.  To do this:

  require 'third_base'
  class YourLibrary
    include ThirdBase
    def today
      Date.today
    end
  end

This makes it so that references to Date within YourLibrary use
ThirdBase::Date, while references to Date outside YourLibrary use the
standard Date class.

=== Use ThirdBase's compatibility mode via the third_base executable

Usage:

  $ third_base irb
  $ third_base mongrel_rails
  $ third_base ruby -rdate -e "p Date.ancestors"

This should be used if you want to make all libraries use ThirdBase's
Date class.  Doing this means that even if they "require 'date'", they
will use ThirdBases's versions.  More explicity, it will define Date
and DateTime as subclasses of ThirdBase::Date and ThirdBase::DateTime,
and make them as API compatible as possible.

You could get this by using "require 'third_base/compat'".
Unfortunately, that doesn't work if you are using rubygems (and
ThirdBase is mainly distributed as a gem), because rubygems indirectly
requires date.

The third_base executable modifies the RUBYLIB and RUBYOPT environment
variables and should ensure that even if a ruby library requires
'date', they will get the ThirdBase version with the compatibility
API.  To use the third_base executable, you just prepend it to any
command that you want to run.

This is the middle ground.  It should work for most applications, but
as ThirdBase's compatibility API is not 100% compatible with the
standard Date class, things can still break. See the next section for
some differences.

If you have good unit tests/specs, you can try using this in your
application then running your specs (e.g. third_base rake spec).
Assuming good coverage, if you have no errors, it should be OK to use,
and you'll get a nice speedup.

== Incompatibilities with the standard Date class when using
third_base/compat

* The marshalling format is different
* The new! class methods take different arguments
* Methods which returned rationals now return integers or floats
* ajd and amjd are now considered the same as jd and mjd, respectively
* The gregorian calendar is now the only calendar used
* All parsed two digit years are mapped to a year between 1969 and 2068
* Default parsing may be different, but the user can modify the parsers
used
* Potentially others, but hopefully anything else can be fixed

== Pluggable Parsers

The standard Date class has a hard coded parsing routine that cannot
be easily modified by the user.  ThirdBase uses a different approach,
by allowing the user to add parsers and change the order of parsers.
There are some default parsers built into ThirdBase's Date and
DateTime, and they should work well for the majority of American
users.  However, there is no guarantee that it includes a parser for
the format you want to parse (though you can add a parser that will do
so).

The user should note that ThirdBases's Date and DateTime classes have
completely separate parsers, and modifying one does not affect the
other.

=== Adding Parser Types

ThirdBase's parsers are separated into parser types.  The Date class
has four parser types built in: :iso, :us, :num, and :eu, of which
only :iso, :us, and :num are used by default.   DateTime has all of
the parser types that Date has, and an additional one called :time.

To add a parser type:

  Date.add_parser_type(:mine)
  DateTime.add_parser_type(:mine)

=== Adding Parsers to Parser Types

A ThirdBase Date/Datetime parser consists of two parts, a regular
expression, and a proc that takes a MatchData object and returns a
hash passed to Date/DateTime.new!.  The proc is only called if the
regular expression matches the string to be parsed, and it can return
nil if it is not able to successfully parse the string (even if the
string matches the regular expression).  To add a parser, you use the
add_parser class method, which takes an argument specifying which
parser family to use, the regular expression, and a block that is used
as a proc for the parser:

To add a parser to a parser type:

  Date.add_parser(:mine, /\Atoday\z/i) do |m|
    t = Time.now {:civil=>[t.year, t.mon, t.day]}
  end
  DateTime.add_parser(:mine, /\Anow\z/i) do |m|
    t = Time.now {:civil=>[t.year, t.mon, t.day], :parts=>[t.hour, \
    t.min, t.sec, t.usec], :offset=>t.utc_offset}
  end

Adding a parser to a parser type adds it to the front of the array of
parsers for that type, so it will be tried before other parsers for
that type.  It is an error to add a parser to a parser type that
doesn't exist.

=== Modifying the Order of Parsers Types

You can change the order in which parsers types are tried by using the
use_parsers class method, which takes multiple arguments specifying
the order of parser types:

To modify the order of parser types:

  Date.use_parsers(:mine, :num, :iso, :us)
  DateTime.use_parsers(:time, :iso, :mine, :eu, :num)

== Performance

=== Synthetic Benchmark

  Date vs. ThirdBase::Date: 20000 Iterations
        user     system      total        real
  Date.new                  1.210000   0.000000   1.210000 ( 1.209048)
  ThirdBase::Date.new       0.240000   0.000000   0.240000 ( 0.237548)
  Date.new >>               4.100000   0.010000   4.110000 ( 4.107972)
  ThirdBase::Date.new >>    0.580000   0.010000   0.590000 ( 0.585797)
  Date.new +                1.580000   0.030000   1.610000 ( 1.613447)
  ThirdBase::Date.new +     0.810000   0.000000   0.810000 ( 0.803092)
  Date.parse                6.180000   0.180000   6.360000 ( 6.364501)
  ThirdBase::Date.parse     0.540000   0.000000   0.540000 ( 0.532560)
  Date.strptime             6.680000   0.030000   6.710000 ( 6.707893)
  ThirdBase::Date.strptime  2.200000   0.040000   2.240000 ( 2.241585)

  DateTime vs. ThirdBase::DateTime: 20000 Iterations
        user     system      total        real
  DT.new                  3.490000   0.270000   3.760000 ( 3.760513)
  ThirdBase::DT.new       0.350000   0.000000   0.350000 ( 0.357525)
  DT.new >>               6.720000   0.230000   6.950000 ( 6.953825)
  ThirdBase::DT.new >>    0.840000   0.020000   0.860000 ( 0.854347)
  DT.new +                3.730000   0.170000   3.900000 ( 3.894309)
  ThirdBase::DT.new +     0.780000   0.060000   0.840000 ( 0.834865)
  DT.parse                8.450000   0.400000   8.850000 ( 8.854514)
  ThirdBase::DT.parse     0.980000   0.040000   1.020000 ( 1.015109)
  DT.strptime            10.860000   0.380000  11.240000 (11.243913)
  ThirdBase::DT.strptime  3.410000   0.160000   3.570000 ( 3.574491)

=== Real World Example

ThirdBase was written to solve a real world problem, slow retrieval of
records from a database because they contained many date fields. The
table in question (employees), has 23 fields, 5 of which are date
fields.  Here are the results of selecting all records for the
database via Sequel, both with and without third_base:

  $ script/benchmarker 100 Employee.all
              user     system      total        real
  #1     25.990000   0.040000  26.030000 ( 27.587781)
  $ third_base script/benchmarker 100 Employee.all
              user     system      total        real
  #1     13.640000   0.100000  13.740000 ( 15.018741)

Note that the times above include the time to query the database and
instantiate all of the Model objects.  In this instance you can see
that ThirdBase doubles performance with no change to the existing
code.  This is do to the fact that previously, date-related code took
about 3/4 of the processing time:

ruby-prof graph profile without ThirdBase for Employee.all 100 times:

75.87% 1.05% 101.51 1.40 0.00 100.12 85500 <Class::Date>#new

ruby-prof graph profile with ThirdBase for Employee.all 100 times:

36.43% 1.29%  18.01 0.64 0.00  17.37 85500 <Class::ThirdBase::Date>#new

ThirdBase still takes up over a third of the processing time, but the
total time it takes has been reduced by a factor of 5.  There may be
opportunities to further speed up ThirdBase--while it was designed to
be faster than the default Date class, there have been no attempts to
optimize its performance.

== License

ThirdBase is released under the MIT License.  See the LICENSE file for
details.

== Author

Jeremy Evans <code / jeremyevans.net>
-- 
Posted via http://www.ruby-forum.com/.