NAME
DateTime::Format::Builder - Create DateTime parser classes and objects.
SYNOPSIS
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 )],
},
],
}
);
DESCRIPTION
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.
TUTORIAL
See DateTime::Format::Builder::Tutorial.
ERROR HANDLING AND BAD PARSES
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'.
SINGLE SPECIFICATIONS
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 *length*s 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.
* label provides a name for the specification and is passed to some of
the callbacks about to mentioned.
* on_match and on_fail are callbacks. Both routines will be called
with parameters of:
* input, being the input to the parser (after any preprocessing
callbacks).
* label, being the label of the parser, if there is one.
* self, being the object on which the method has been invoked
(which may just be a class name). Naturally, you can then invoke
your own methods on it do get information you want.
* args, being an arrayref of any passed arguments, if any. If
there were no arguments, then this parameter is not given.
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:
* input being the datetime string the parser was given (if using
multiple specifications and an overall *preprocess* then this is
the date after it's been through that preprocessor).
* parsed being the state of parsing so far. Usually empty at this
point unless an overall *preprocess* was given. Items may be
placed in it and will be given to any postprocessor and
`DateTime->new' (unless the postprocessor deletes it).
* self, args, label as per *on_match* and *on_fail*.
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:
* DateTime::Format::Builder::Parser::Regex - provides regular
expression based parsing.
* DateTime::Format::Builder::Parser::Strptime - provides strptime
based parsing.
Subroutines / coderefs as specifications.
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.
Callbacks
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.
MULTIPLE SPECIFICATIONS
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.
* on_fail should be a reference to a subroutine that is called if the
parser fails. If this is not provided, the default action is to call
`DateTime::Format::Builder::on_fail', or the `on_fail' method of the
subclass of DTFB that was used to create the parser.
EXECUTION FLOW
Builder allows you to plug in a fair few callbacks, which can make
following how a parse failed (or succeeded unexpectedly) somewhat
tricky.
For Single Specifications
A single specification will do the following:
User calls parser:
my $dt = $class->parse_datetime( $string );
1 *preprocess* is called. It's given `$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.
2 *regex* is applied.
3 If *regex* did not match, then *on_fail* is called (and is given
`$date' and also *label* if it was defined). Any return value is
ignored and the next thing is for the single parser to return
`undef'.
If *regex* did match, then *on_match* is called with the same
arguments as would be given to *on_fail*. The return value is
similarly ignored, but we then move to step 4 rather than exiting
the parser.
4 *postprocess* is called with `$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.
5 `DateTime->new()' is called and the user is given the resultant
`DateTime' object.
See the section on error handling regarding the `undef's mentioned
above.
For Multiple Specifications
With multiple specifications:
User calls parser:
my $dt = $class->complex_parse( $string );
1 The overall *preprocess*or is called and is given `$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 `$p' is given to each
of the individual parsers. This is so parsers won't accidentally
pollute each other's workspace.
2 If an appropriate length specific parser is found, then it is called
and the single parser flow (see the previous section) is followed,
and the parser is given a copy of `$p' and the return value of the
overall *preprocess*or 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!
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 `undef's mentioned
above.
METHODS
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
`import()' is a wrapper for `create_class()'. If you specify the *class*
option (see documentation for `create_class()') it will be ignored.
create_class
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 is also optional and specifies the value to give `$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.
SUBCLASSING
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.
create_method
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.
on_fail
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'.
USING BUILDER OBJECTS aka USERS USING BUILDER
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.
new
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();
clone
Provided for those who prefer an explicit `clone()' method rather than
using `new()' as an object method.
my $clone_of_clone = $clone->clone();
parser
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.
set_parser
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.
get_parser
Returns the parser the object is using.
my $code = $parser->get_parser();
parse_datetime
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.
format_datetime
If you call this function, it will throw an errror.
LONGER EXAMPLES
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.
THANKS
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 F�rber (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
Support for this module is provided via the
[email protected] 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
[email protected]
This makes it much easier for me to track things and thus means your
problem is less likely to be neglected.
LICENCE AND COPYRIGHT
Copyright E<copy> 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.
AUTHOR
Originally written by Iain Truskett <
[email protected]>, who died on
December 29, 2003.
Maintained by Dave Rolsky <
[email protected]>.
SEE ALSO
`
[email protected]' mailing list.
http://datetime.perl.org/
perl, DateTime, DateTime::Format::Builder::Tutorial,
DateTime::Format::Builder::Parser
