DateTime::Format::Builder - Create DateTime parser classes and objects.
package DateTime::Format::Brief;
our $VERSION = '0.07';
use DateTime::Format::Builder
(
parsers => {
parse_datetime => [
{
regex => qr/^(\d{4})(\d\d)(\d\d)(\d\d)(\d\d)(\d\d)$/,
params => [qw( year month day hour minute second )],
},
{
regex => qr/^(\d{4})(\d\d)(\d\d)$/,
params => [qw( year month day )],
},
],
}
);
DateTime::Format::Builder creates DateTime parsers. Many string formats of dates and times are simple and just require a basic regular expression to extract the relevant information. Builder provides a simple way to do this without writing reams of structural code.
Builder provides a number of methods, most of which you'll never need, or at least rarely need. They're provided more for exposing of the module's innards to any subclasses, or for when you need to do something slightly beyond what I expected.
See DateTime::Format::Builder::Tutorial.
Often, I will speak of undef being returned, however
that's not strictly true.
When a simple single specification is given for a method,
the method isn't given a single parser directly. It's given
a wrapper that will call on_fail() if the single parser
returns undef. The single parser must return undef so
that a multiple parser can work nicely and actual errors can
be thrown from any of the callbacks.
Similarly, any multiple parsers will only call on_fail()
right at the end when it's tried all it could.
on_fail() (see later) is defined, by default,
to throw an error.
Multiple parser specifications can also specify on_fail
with a coderef as an argument in the options block. This
will take precedence over the inheritable and over-ridable
method.
That said, don't throw real errors from callbacks in multiple parser specifications unless you really want parsing to stop right there and not try any other parsers.
In summary: calling a method will result in either a
DateTime object being returned or an error being thrown
(unless you've overridden on_fail() or
create_method(), or you've specified a on_fail key to
a multiple parser specification).
Individual parsers (be they multiple parsers or single
parsers) will return either the DateTime object or
undef.
A single specification is a hash ref of instructions on how to create a parser.
The precise set of keys and values varies according to parser type. There are some common ones though:
length is an optional parameter that can be used to specify that this particular regex is only applicable to strings of a certain fixed length. This can be used to make parsers more efficient. It's strongly recommended that any parser that can use this parameter does.
You may happily specify the same length twice. The parsers will be tried in order of specification.
You can also specify multiple lengths by giving it an arrayref of numbers rather than just a single scalar. If doing so, please keep the number of lengths to a minimum.
If any specifications without lengths are given and the particular length parser fails, then the non-length parsers are tried.
This parameter is ignored unless the specification is part of a multiple parser specification.
on_match and on_fail are callbacks. Both routines will be called with parameters of:
These routines will be called depending on whether the regex match succeeded or failed.
preprocess is a callback provided for cleaning up input prior to parsing. It's given a hash as arguments with the following keys:
DateTime->new (unless the
postprocessor deletes it).
The return value from the routine is what is given to the regex. Note that this is last code stop before the match.
Note: mixing length and a preprocess that modifies
the length of the input string is probably not what you
meant to do. You probably meant to use the
multiple parser variant of preprocess which is done
before any length calculations. This single parser variant
of preprocess is performed after any length
calculations.
postprocess is the last code stop before
DateTime->new() is called. It's given the same
arguments as preprocess. This allows it to modify the
parsed parameters after the parse and before the creation
of the object. For example, you might use:
{
regex => qr/^(\d\d) (\d\d) (\d\d)$/,
params => [qw( year month day )],
postprocess => \&_fix_year,
}
where _fix_year is defined as:
sub _fix_year
{
my %args = @_;
my ($date, $p) = @args{qw( input parsed )};
$p->{year} += $p->{year} > 69 ? 1900 : 2000;
return 1;
}
This will cause the two digit years to be corrected according to the cut off. If the year was '69' or lower, then it is made into 2069 (or 2045, or whatever the year was parsed as). Otherwise it is assumed to be 19xx. The DateTime::Format::Mail module uses code similar to this (only it allows the cut off to be configured and it doesn't use Builder).
Note: It is very important to return an explicit value
from the postprocess callback. If the return value is
false then the parse is taken to have failed. If the return
value is true, then the parse is taken to have succeeded and
DateTime->new() is called.
See the documentation for the individual parsers for their valid keys.
Parsers at the time of writing are:
A single parser specification can be a coderef. This was added mostly because it could be and because I knew someone, somewhere, would want to use it.
If the specification is a reference to a piece of code, be
it a subroutine, anonymous, or whatever, then it's passed
more or less straight through. The code should return
undef in event of failure (or any false value,
but undef is strongly preferred), or a true value in the
event of success (ideally a DateTime object or some
object that has the same interface).
This all said, I generally wouldn't recommend using this feature unless you have to.
I mention a number of callbacks in this document.
Any time you see a callback being mentioned, you can, if you like, substitute an arrayref of coderefs rather than having the straight coderef.
These are very easily described as an array of single specifications.
Note that if the first element of the array is an arrayref, then you're specifying options.
preprocess lets you specify a preprocessor that is called before any of the parsers are tried. This lets you do things like strip off timezones or any unnecessary data. The most common use people have for it at present is to get the input date to a particular length so that the length is usable (DateTime::Format::ICal would use it to strip off the variable length timezone).
Arguments are as for the single parser preprocess variant with the exception that label is never given.
DateTime::Format::Builder::on_fail, or the on_fail
method of the subclass of DTFB that was used to create the
parser.
Builder allows you to plug in a fair few callbacks, which can make following how a parse failed (or succeeded unexpectedly) somewhat tricky.
A single specification will do the following:
User calls parser:
my $dt = $class->parse_datetime( $string );
$string and a
reference to the parsing workspace hash, which we'll call
$p. At this point, $p is empty. The return value is
used as $date for the rest of this single parser.
Anything put in $p is also used for the rest of this
single parser.
If regex did not match, then on_fail is called (and is given
$date and also label if it was defined). Any return
value is ignored and the next thing is for the single
parser to return undef.
If regex did match, then on_match is called with the same arguments as would be given to on_fail. The return value is similarly ignored, but we then move to step 4 rather than exiting the parser.
$date and a filled out
$p. The return value is taken as a indication of whether
the parse was a success or not. If it wasn't a success then
the single parser will exit at this point, returning undef.
DateTime->new() is called and the user is given the
resultant DateTime object.
See the section on error handling
regarding the undefs mentioned above.
With multiple specifications:
User calls parser:
my $dt = $class->complex_parse( $string );
The overall preprocessor is called and is given $string
and the hashref $p (identically to the per parser
preprocess mentioned in the previous flow).
If the callback modifies $p then a copy of $p is
given to each of the individual parsers. This is so parsers
won't accidentally pollute each other's workspace.
If an appropriate length specific parser is found, then it
is called and the single parser flow (see the previous
section) is followed, and the parser is given a copy of
$p and the return value of the overall preprocessor as
$date.
If a DateTime object was returned so we go straight back
to the user.
If no appropriate parser was found, or the parser returned
undef, then we progress to step 3!
Any non-length based parsers are tried in the order they were specified.
For each of those the single specification flow above is performed, and is given a copy of the output from the overall preprocessor.
If a real DateTime object is returned then we exit back
to the user.
If no parser could parse, then an error is thrown.
See the section on error handling
regarding the undefs mentioned above.
In the general course of things you won't need any of the methods. Life often throws unexpected things at us so the methods are all available for use.
import() is a wrapper for create_class(). If you
specify the class option (see documentation for
create_class()) it will be ignored.
This method can be used as the runtime equivalent of
import(). That is, it takes the exact same parameters as
when one does:
use DateTime::Format::Builder ( blah blah blah )
That can be (almost) equivalently written as:
use DateTime::Format::Builder; DateTime::Format::Builder->create_class( blah blah blah );
The difference being that the first is done at compile time while the second is done at run time.
In the tutorial I said there were only two parameters at present. I lied. There are actually three of them.
parsers takes a hashref of methods and their parser specifications. See the tutorial above for details.
Note that if you define a subroutine of the same name as one of the methods you define here, an error will be thrown.
constructor determines whether and how to create a
new() function in the new class. If given a true value, a
constructor is created. If given a false value, one isn't.
If given an anonymous sub or a reference to a sub then that
is used as new().
The default is 1 (that is, create a constructor using
our default code which simply creates a hashref and blesses
it).
If your class defines its own new() method it will not be
overwritten. If you define your own new() and also tell
Builder to define one an error will be thrown.
verbose takes a value. If the value is undef, then
logging is disabled. If the value is a filehandle then
that's where logging will go. If it's a true value, then
output will go to STDERR.
Alternatively, call $DateTime::Format::Builder::verbose()
with the relevant value. Whichever value is given more
recently is adhered to.
Be aware that verbosity is a global wide setting.
class is optional and specifies the name of the class in which to create the specified methods.
If using this method in the guise of import() then this
field will cause an error so it is only of use when calling
as create_class().
$VERSION in the class. It's generally not recommended
unless you're combining with the class option. A
ExtUtils::MakeMaker / CPAN compliant version
specification is much better.
In addition to creating any of the methods it also creates a
new() method that can instantiate (or clone) objects.
In the rest of the documentation I've often lied in order to get some of the ideas across more easily. The thing is, this module's very flexible. You can get markedly different behaviour from simply subclassing it and overriding some methods.
Given a parser coderef, returns a coderef that is suitable to be a method.
The default action is to call on_fail() in the event of a
non-parse, but you can make it do whatever you want.
This is called in the event of a non-parse (unless you've
overridden create_method() to do something else.
The single argument is the input string. The default action
is to call croak(). Above, where I've said parsers or
methods throw errors, this is the method that is doing the
error throwing.
You could conceivably override this method to, say, return
undef.
The methods listed in the METHODS section are all you generally need when creating your own class. Sometimes you may not want a full blown class to parse something just for this one program. Some methods are provided to make that task easier.
The basic constructor. It takes no arguments, merely returns
a new DateTime::Format::Builder object.
my $parser = DateTime::Format::Builder->new();
If called as a method on an object (rather than as a class method), then it clones the object.
my $clone = $parser->new();
Provided for those who prefer an explicit clone() method
rather than using new() as an object method.
my $clone_of_clone = $clone->clone();
Given either a single or multiple parser specification, sets the object to have a parser based on that specification.
$parser->parser(
regex => qr/^ (\d{4}) (\d\d) (\d\d) $/x;
params => [qw( year month day )],
);
The arguments given to parser() are handed directly to
create_parser(). The resultant parser is passed to
set_parser().
If called as an object method, it returns the object.
If called as a class method, it creates a new object, sets its parser and returns that object.
Sets the parser of the object to the given parser.
$parser->set_parser( $coderef );
Note: this method does not take specifications. It also does not take anything except coderefs. Luckily, coderefs are what most of the other methods produce.
The method return value is the object itself.
Returns the parser the object is using.
my $code = $parser->get_parser();
Given a string, it calls the parser and returns the
DateTime object that results.
my $dt = $parser->parse_datetime( "1979 07 16" );
The return value, if not a DateTime object, is whatever
the parser wants to return. Generally this means that if the
parse failed an error will be thrown.
If you call this function, it will throw an errror.
Some longer examples are provided in the distribution. These implement some of the common parsing DateTime modules using Builder. Each of them are, or were, drop in replacements for the modules at the time of writing them.
Dave Rolsky (DROLSKY) for kickstarting the DateTime project, writing DateTime::Format::ICal and DateTime::Format::MySQL, and some much needed review.
Joshua Hoblitt (JHOBLITT) for the concept, some of the API, impetus for writing the multilength code (both one length with multiple parsers and single parser with multiple lengths), blame for the Regex custom constructor code, spotting a bug in Dispatch, and more much needed review.
Kellan Elliott-McCrea (KELLAN) for even more review, suggestions, DateTime::Format::W3CDTF and the encouragement to rewrite these docs almost 100%!
Claus Färber (CFAERBER) for having me get around to fixing the auto-constructor writing, providing the 'args'/'self' patch, and suggesting the multi-callbacks.
Rick Measham (RICKM) for DateTime::Format::Strptime which Builder now supports.
Matthew McGillis for pointing out that on_fail overriding
should be simpler.
Simon Cozens (SIMON) for saying it was cool.
Support for this module is provided via the datetime@perl.org email list. See http://lists.perl.org/ for more details.
Alternatively, log them via the CPAN RT system via the web or email:
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DateTime%3A%3AFormat%3A%3ABuilder
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.
Copyright © Iain Truskett, 2003. All rights reserved.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.000 or, at your option, any later version of Perl 5 you may have available.
The full text of the licences can be found in the Artistic and COPYING files included with this module, or in perlartistic and perlgpl as supplied with Perl 5.8.1 and later.
Originally written by Iain Truskett <spoon@cpan.org>, who died on December 29, 2003.
Maintained by Dave Rolsky <autarch@urth.org>.
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perl, DateTime, DateTime::Format::Builder::Tutorial, DateTime::Format::Builder::Parser