man Data::Flow () - Perl extension for simple-minded recipe-controlled build of data.
NAME
Data::Flow - Perl extension for simple-minded recipe-controlled build of data.
SYNOPSIS
use Data::Flow;
$recipes = { path => { default => './MANIFEST'},
contents => { prerequisites => ['path', 'x'] ,
process =>
sub {
my $data = shift;
$data->{ shift() } = `cat $data->get('path')`
x $data->get('x');
}
},
};
$request = new Data::Flow $recipes;
$request->set( x => 1);
print $request->get('contents');
tie %request, Data::Flow, $recipes;
$request{x} = 1;
print $request{contents};
DESCRIPTION
The module Data::Flow provides its services via objects. The objects may be obtained by the usual
$request = new Data::Flow $recipes;
paradigm. The argument CW$recipes is a hash reference, which provides the rules for request processing. The objects support two methods, set() and get(). The first one is used to provide input data for processing, the second one to obtain the output.
The unit of requested information is a field. The method set() takes a pair CWfield => value, the method get() takes one argument: the CWfield.
Every object is created without any fields filled, but it knows how to construct fields basing on other fields or some global into. This knowledge is provided in the argument CW$recipe of the new() function. This is a reference to a hash, keyed by fields. The values of this hash are hash references themselves, which describe how to acquire the field which is the corresponding key of the initial hash.
The internal hashes may have the following keys: describes the default value for the key, if none is provided by set(). The value becomes the value of the field of the object. No additional processing is performed. Example:
default => $Config{installdir}
gives the fields which are needed for the construction of the given
field. The corresponding value is an array references. The array
contains the required fields.
If CWdefaults did not satisfy the request for a field, but
CW$recipe->{field}{prerequisites} exists, the required
fields are build before any further processing is done. Example:
prerequisites => [ qw(prefix arch) ]contains the rule to build the field. The value is a reference to a subroutine taking 2 arguments: the object CW$request, and the name of the required field. It is up to the subroutine to actually fill the corresponding field of CW$data, an error condition is raised if it did not. Example:
process => sub { my $data = shift;
$data->set( time => localtime(time) ) }
the corresponing value has the same meaning as for CWprocess, but the
return value of the subroutine is used as the value of the
field. Example:
output => sub { localtime(time) }
contains the rule to build the field basing on other fields. The value
is a reference to an array. The first element of the array is a
reference to a subroutine, the rest contains names of the fields. When
the subroutine is called, the arguments are the values of fields of
the object CW$request which appear in the array (in the same order). The
return value of the subroutine is used as the value of the
field. Example:
filter => [ sub { shift + shift },
'first_half', 'second_half' ]
Note that the mentioned field will be automatically marked as
prerequisites.
is similar to CWfilter, but the first argument is the name of the
method to call, second one is the name of the package to use for the
method invocation. The rest contains names of field to provide as
method arguments. Example:
class_filter => [ 'new', 'FileHandle', 'filename' ]is similar to CWclass_filter, but the second argument is the name of the field which is used to call the method upon. Example:
method_filter => [ 'show', 'widget_name', 'current_display' ]
Tied interface
The access to the same functionality is available via tied hash interface.
AUTHOR
Ilya Zakharevich, ilya@math.ohio-state.edu