Benjamin Trott
and 1 contributors




    my @data = ( 1 .. 15 );

    my $machine = Data::ConveyorBelt->new;
    $machine->getter( sub {
        my( $limit, $offset ) = @_;
        $offset ||= 0;
        return [ @data[ $offset .. $offset + $limit ] ];
    } );

    $machine->add_filter( sub {
        my( $data ) = @_;
        return [ grep { $_ % 2 == 1 } @$data ];
    } );
    my $data = $machine->fetch( limit => 5 );




Returns a new Data::ConveyorBelt instance.

$machine->getter( [ \&getter ] )

Gets/sets the getter subroutine \&getter that represents the list of items in your data source. Required before calling fetch.

A getter subroutine will be passed two arguments: the number of items to return, and the offset into the list (0-based). It must return a reference to the matching list of items.

$machine->add_filter( \&filter )

Adds a filter subroutine \&filter to your chain of filters.

A filter will be passed a reference to a list of items as returned either from your getter or from a previous filter in the chain. A filter must return a reference to a list of items.

A filter can alter the size of the list of items, either removing or expanding items in the list. It can also transform the items in the list.

$machine->fetch( %param )

Fetches a list of items from your data source, passes them through your filters, and returns a reference to a list of items.

You must install a getter before calling fetch, but you don't have to install any filters. Running fetch without any filters does what you'd expect: it returns the values directly from your data source, unmodified and unfiltered.

%param can contain:

  • limit

    The number of items to return. Required.

  • offset

    The offset into the full list of items (0-based). Optional; defaults to 0.

  • chunk_size

    The number of items to request at a time from your getter function.

    For example, if your getter has high latency (reading from a network resource, for example), and if you suspect that your filters will be fairly aggressive--and will end up removing a good percentage of the items returned from the getter--you may want to fetch larger chunks of data at a time.

    Optional; defaults to the same value as limit.


Data::ConveyorBelt is free software; you may redistribute it and/or modify it under the same terms as Perl itself.


Except where otherwise noted, Data::ConveyorBelt is Copyright 2007 Six Apart,