[mplspm]: A project for MPM

[Dave Rolsky]

So we've talked a bit about this in the past, and at the last meeting we
briefly mentioned the idea of taking on dates & times as our PM project.

I think this'd be a really cool thing to do, and there is a desperate need
for somebodies in the Perl community to really try to improve the
situation in regards to date/time modules.

Here's some thing that I think we could work on, in order of increasing
difficulty.

1. A document comparing all the major date & time modules for Perl.

Things to look at could include:

-- module scope (how much stuff it does)
-- epoch only or not?
-- does date math?
-- OO or functions?
-- special features?
-- license
-- strengths/weakness (somewhat subjective but that's ok)


2. Take the above and turn it into datetime.perl.org.  This could be a
website we collectively maintained that hosted the above document and
perhaps other resources (I'm not sure exactly what though).


3. Fill in the gaps.  For example, AFAIK there is no module for Perl that
handles time zones completely and correctly.  In fact, the only module I
know of for Perl that handles time zones at all is Time::Zone, which AFAIC
is close to useless.  All it does is parse Unix-style TZ env variables and
return offsets.  That's not very helpful because it uses the older style
3/4 letter zones like 'cst', which just doesn't cut it these days.


4. Try to come up with _the_ one way to do it ;)  I say this sort of
tongue in cheek, but only sort of.  Perl has a lot of different date/time
modules, each of which individually have very interesting and useful
features, but none of which by itself does everything.  Since they all
have radically different interfaces, working with more than 1 module at a
time is a big pain in the ass.

Initially, we might just try to design a single interface that hides the
details of the different modules, and presents a single unified way of
doing all the useful things one could do (parsing, date math, output in
different formats, etc.).  Later, we might start actually ripping code out
of different modules and putting together our own suite of modules that
represents the best of Perl's date/time code.


If there's any takers for #1, here's a reasonably complete list of
"interesting" Perl date/time modules along with my comments about them:


- Time::Piece (and Time::Seconds) - nice interface, nice simply date math,
but only handles epoch times, which is a drag.  See also my
Time::Piece::MySQL module, which adds some mysql-specific bits.  Similar
modules for other DBs/external resources can be added just as easily.

- Class::Date & Date::Handler - kind of like Time::Piece on steroids, but
I don't see why they can't all be integrated.

- Date::Manip - ridiculously large amount of code.  crapulous interface.
freaking brilliant parsing code that handles things like "2nd day after
next Tuesday" or "the first day of the last week of the next month".  Also
has some internationalization bits for parsing, which is doubly slick.  If
this thing could return a Time::Piece object (and T::P handled times
outside of the epoch), I'd be in heaven.

- Date::Calc - lots of nice date math functions.  Stupid interface
(Function_Names_Like_This).  Written in C so presumably its fast.

-- Date::Calc::Object - OO interface over Date::Calc.  Interesting.  Also
has Date delta objects.  Cool!  Works with Date::Calc functions, which
have stupid names, but making a wrapper for that wouldn't be too hard.

-- Date::Calendar - seems quite useful

- Date::Parse - lightweight so it's a good choice if you know that you'll
never exceed its limitations.  But those limitations are pretty big cause
it doesn't do much.

- Date::Format - basically strftime in Perl.  Time::Piece provides the
same thing.

- Time::Zone - see above

- Time::Human - could be useful for some apps

- Time::TAI64 - currently says not to use it, but it could provide
something useful is author releases, stable, documented version.  Relies
on libtai by Dan J Bernstein, known psycho.

- Date::ICal - nice interface, would mesh well with Time::Piece.  ICal is
important for calendaring apps.  Date::ICal is part of the reefknot
project, which aimed at implementing all of iCal in Perl, but seems to be
more or less defunct.

- Date::Interval - could be interesting but seems to have a weird API.


And quite a few more.  Also check out the now defunct reefknot project at
www.reefknot.org, which has more resources on dates & times.

So if people are interested perhaps they could pick a few modules to do
writeups on.  I think something like this would be good:

 scope: small, medium, big (how many different things it tries to accomplish)
 interface: OO / functions / both?
 focus (or focii): parsing, output formatting, date math, business dates, calendars, date intervals, etc.
 license - important if we ever want to try to combine them

And then maybe 2-4 paragraphs talking about special features, strengths
and weaknesses, relationships to other modules.


Any takers?


-dave

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