NAME¶
DateTime::Format::Builder::Tutorial - Quick class on using Builder
CREATING A CLASS¶
As most people who are writing modules know, you start a package with a package
declaration and some indication of module version:
package DateTime::Format::ICal;
our $VERSION = '0.04';
After that, you call Builder with some options. There are only a few (detailed
later). Right now, we're only interested in
parsers.
use DateTime::Format::Builder
(
parsers => {
...
}
);
The
parsers option takes a reference to a hash of method names and
specifications:
parsers => {
parse_datetime => ... ,
parse_datetime_with_timezone => ... ,
...
}
Builder will create methods in your class, each method being a parser that
follows the given specifications. It is
strongly recommended that one
method is called
parse_datetime, be it a Builder created method or one
of your own.
In addition to creating any of the parser methods it also creates a
"new()" method that can instantiate (or clone) objects of this
class. This behaviour can be modified with the
constructor option, but
we don't need to know that yet.
Each value corresponding to a method name in the parsers list is either a single
specification, or a list of specifications. We'll start with the simple case.
parse_briefdate => {
params => [ qw( year month day ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)$/,
},
This will result in a method named
parse_briefdate which will take
strings in the form 20040716 and return DateTime objects representing that
date. A user of the class might write:
use DateTime::Format::ICal;
my $date = "19790716";
my $dt = DateTime::Format::ICal->parse_briefdate( $date );
print "My birth month is ", $dt->month_name, "\n";
The "regex" is applied to the input string, and if it matches, then
$1, $2, ... are mapped to the
params given and handed to
"DateTime->new()". Essentially:
my $rv = DateTime->new( year => $1, month => $2, day => $3 );
There are more complicated things one can do within a single specification, but
we'll cover those later.
Often, you'll want a method to be able to take one string, and run it against
multiple parser specifications. It would be very irritating if the user had to
work out what format the datetime string was in and then which method was most
appropriate.
So, Builder lets you specify multiple specifications:
parse_datetime => [
{
params => [ qw( year month day hour minute second ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)(\d\d)(\d\d)$/,
},
{
params => [ qw( year month day hour minute ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)(\d\d)$/,
},
{
params => [ qw( year month day hour ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)$/,
},
{
params => [ qw( year month day ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)$/,
},
],
It's an arrayref of specifications. A parser will be created that will try each
of these specifications sequentially, in the order you specified.
There's a flaw with this though. In this example, we're building a parser for
ICal datetimes. One can place a timezone id at the start of an ICal datetime.
You might extract such an id with the following code:
if ( $date =~ s/^TZID=([^:]+):// )
{
$time_zone = $1;
}
# Z at end means UTC
elsif ( $date =~ s/Z$// )
{
$time_zone = 'UTC';
}
else
{
$time_zone = 'floating';
}
$date would end up without the id, and $time_zone would contain something
appropriate to give to DateTime's
set_time_zone method, or
time_zone argument.
But how to get this scrap of code into your parser? You might be tempted to call
the parser something else and build a small wrapper. There's no need though
because an option is provided for preprocesing dates:
parse_datetime => [
[ preprocess => \&_parse_tz ], # Only changed line!
{
params => [ qw( year month day hour minute second ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)(\d\d)(\d\d)$/,
},
{
params => [ qw( year month day hour minute ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)(\d\d)$/,
},
{
params => [ qw( year month day hour ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)$/,
},
{
params => [ qw( year month day ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)$/,
},
],
It will necessitate
_parse_tz to be written, and that routine looks like
this:
sub _parse_tz
{
my %args = @_;
my ($date, $p) = @args{qw( input parsed )};
if ( $date =~ s/^TZID=([^:]+):// )
{
$p->{time_zone} = $1;
}
# Z at end means UTC
elsif ( $date =~ s/Z$// )
{
$p->{time_zone} = 'UTC';
}
else
{
$p->{time_zone} = 'floating';
}
return $date;
}
On input it is given a hash containing two items: the input date and a hashref
that will be used in the parsing. The return value from the routine is what
the parser specifications will run against, and anything in the
parsed
hash ($p in the example) will be put in the call to
"DateTime->new(...)".
So, we now have a happily working ICal parser. It parses the assorted formats,
and can also handle timezones. Is there anything else it needs to do? No. But
we can make it work more efficiently.
At present, the specifications are tested sequentially. However, each one
applies to strings of particular lengths. Thus we could be efficient and have
the parser only test the given strings against a parser that handles that
string length. Again, Builder makes it easy:
parse_datetime => [
[ preprocess => \&_parse_tz ],
{
length => 15, # We handle strings of exactly 15 chars
params => [ qw( year month day hour minute second ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)(\d\d)(\d\d)$/,
},
{
length => 13, # exactly 13 chars...
params => [ qw( year month day hour minute ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)(\d\d)$/,
},
{
length => 11, # 11..
params => [ qw( year month day hour ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)$/,
},
{
length => 8, # yes.
params => [ qw( year month day ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)$/,
},
],
Now the created parser will create a parser that only runs specifications
against appropriate strings.
So our complete code looks like:
package DateTime::Format::ICal;
use strict;
our $VERSION = '0.04';
use DateTime::Format::Builder
(
parsers => {
parse_datetime => [
[ preprocess => \&_parse_tz ],
{
length => 15,
params => [ qw( year month day hour minute second ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)(\d\d)(\d\d)$/,
},
{
length => 13,
params => [ qw( year month day hour minute ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)(\d\d)$/,
},
{
length => 11,
params => [ qw( year month day hour ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)T(\d\d)$/,
},
{
length => 8,
params => [ qw( year month day ) ],
regex => qr/^(\d\d\d\d)(\d\d)(\d\d)$/,
},
],
},
);
sub _parse_tz
{
my %args = @_;
my ($date, $p) = @args{qw( input parsed )};
if ( $date =~ s/^TZID=([^:]+):// )
{
$p->{time_zone} = $1;
}
# Z at end means UTC
elsif ( $date =~ s/Z$// )
{
$p->{time_zone} = 'UTC';
}
else
{
$p->{time_zone} = 'floating';
}
return $date;
}
1;
And that's an ICal parser. The actual DateTime::Format::ICal module also
includes formatting methods and parsing for durations, but Builder doesn't
support those yet. A drop in replacement (at the time of writing the
replacement) can be found in the
examples directory of the Builder
distribution, along with similar variants of other common modules.
SUPPORT¶
Any errors you see in this document, please log them with CPAN RT system via the
web or email:
http://perl.dellah.org/rt/dtbuilder
bug-datetime-format-builder@rt.cpan.org
This makes it much easier for me to track things and thus means your problem is
less likely to be neglected.
LICENSE AND COPYRIGHT¶
Copyright X Iain Truskett, 2003. All rights reserved.
You can redistribute this document and/or modify it under the same terms as Perl
itself.
The full text of the licenses can be found in the
Artistic and
COPYING files included with this document.
AUTHOR¶
Iain Truskett <spoon@cpan.org>
SEE ALSO¶
"datetime@perl.org" mailing list.
http://datetime.perl.org/
perl, DateTime, DateTime::Format::Builder