[ruby-core:33246] [Ruby 1.9-Feature#4068][Open] Replace current standard Date/DateTime library with home_run

Feature #4068: Replace current standard Date/DateTime library with home_run
http://redmine.ruby-lang.org/issues/show/4068

Author: Jeremy Evans
Status: Open, Priority: Normal
Assigned to: tadayoshi funaba

The current standard date library is slow enough to be the bottleneck in many programs.  I have written a replacement for it in C (named home_run) that is much faster while attempting to be mostly compatible.  I open this ticket in the hope that home_run can replace the current standard date library in a future version of ruby.

First, the code is at: https://github.com/jeremyevans/home_run

As it states in the README, here are the known differences from the current standard library:

* Written in C (mostly) instead of ruby. Stores information in a C structure, and therefore has a range limitation. home_run cannot handle dates after 5874773-08-15 or before -5877752-05-08 on 32-bit platforms (with larger limits for 64-bit platforms).
* The Date class does not store fractional days (e.g. hours, minutes), or offsets. The DateTime class does handle fractional days and offsets.
* The DateTime class stores fractional days as the number of nanoseconds since midnight, so it cannot deal with differences less than a nanosecond.
* Neither Date nor DateTime uses rational. Places where the standard library returns rationals, home_run returns integers or floats.
* Because rational is not used, it is not required. This can break other libraries that use rational without directly requiring it.
* There is no support for modifying the date of calendar reform, the sg arguments are ignored and the Gregorian calendar is always used. This means that julian day 0 is -4173-11-24, instead of -4712-01-01.
* The undocumented Date#strftime format modifiers are not supported.
* The DateTime offset is checked for reasonableness. home_run does not support offsets with an absolute difference of more than 14 hours from UTC.
* DateTime offsets are stored in minutes, so it will round offsets with fractional minutes to the nearest minute.
* All public class and instance methods for both Date and DateTime are implemented, except that the allocate class method is not available and on 1.9, _dump and _load are used instead of marshal_dump and marshal_load.
* Only the public API is compatible, the private methods in the standard library are not implemented.
* The marshalling format differs from the one used by the standard library. Note that the 1.8 and 1.9 standard library date marshalling formats differ from each other.
* Date#step treats the step value as an integer, so it cannot handle steps of fractional days. DateTime#step can handle fractional day steps, though.
* When parsing the %Q modifier in _strptime, the hash returned includes an Integer :seconds value and a Float :sec_fraction value instead of a single rational :seconds value.
* The string returned by #inspect has a different format, since it doesn't use rational.
* The conversion of 2-digit years to 4-digit years in Date._parse is set to true by default. On ruby 1.8, the standard library has it set to false by default.
* You can use the Date::Format::STYLE hash to change how to parse DD/DD/DD and DD.DD.DD date formats, allowing you to get ruby 1.9 behavior on 1.8 or vice-versa. This is probably the only new feature in that isn't in the standard library.

From previous discussions on ruby-core, the following things will probably need to be changed before home_run could replace the current standard date library:

* The marshalling format needs to be made compatible with the current standard library.
* The specs needs to be converted from MSpec to minitest/spec for inclusion in ruby.
* The RubySpec project also needs to have the MSpecs added, with the appropriate version guards where behavior has changed.
* Where home_run now returns floats, it should return rationals instead.

I'm willing to make these changes and other reasonable changes in order to get this included in ruby.  I just need to know what all of the required changes are.


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