Flow
Section: User Contributed Perl Documentation
(3)
Updated: perl 5.004, patch 55
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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 $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 field => value, the method get() takes one
argument: the field.
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 $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:
- default
-
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}
- prerequisites
-
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 defaults did not satisfy the request for a field, but
$recipe->{field}{prerequisites} exists, the required
fields are build before any further processing is done. Example:
prerequisites => [ qw(prefix arch) ]
- process
-
contains the rule to build the field. The value is a reference to a
subroutine taking 2 arguments: the object $request, and the name of
the required field. It is up to the subroutine to actually fill the
corresponding field of $data, an error condition is raised if it did
not. Example:
process => sub { my $data = shift;
$data->set( time => localtime(time) ) }
- output
-
the corresponing value has the same meaning as for process, but the
return value of the subroutine is used as the value of the
field. Example:
output => sub { localtime(time) }
- filter
-
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 $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.
- class_filter
-
is similar to filter, 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' ]
- method_filter
-
is similar to class_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
SEE ALSO
perl(1), make(1).
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- Tied interface
-
- AUTHOR
-
- SEE ALSO
-
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Time: 23:58:16 GMT, February 15, 2023