Data::Tumbler - Dynamic generation of nested combinations of variants


    $tumbler = Data::Tumbler->new(

        add_path => sub {
            my ($path, $name) = @_;
            return [ @$path, $name ];

        add_context => sub {
            my ($context, $value) = @_;
            return [ @$context, $value ]

        consumer  => sub {
            my ($path, $context, $payload) = @_;
            print "@$path: @$context\n";

        [   # provider code refs
            sub { (red => 42, green => 24, mauve => 19) },
            sub { (circle => 1, square => 2) },
            # ...
        [], # initial path
        [], # initial context
        [], # initial payload

The consumer code outputs:

    green circle: 24 1
    green square: 24 2
    mauve circle: 19 1
    mauve square: 19 2
    red circle: 42 1
    red square: 42 2

Here's a longer example showing more features:

    use List::Util qw(sum);

    $tumbler = Data::Tumbler->new(

        # The default add_path is as shown above
        # The default add_context is as shown above

        consumer  => sub {
            my ($path, $context, $payload) = @_;
            printf "path: %-20s  context: %-12s  payload: %s\n",
                join("/",  @$path),
                join(", ", @$context),
                join(", ", map { "$_=>$payload->{$_}" } sort keys %$payload);

        [   # providers
            sub {
                my ($path, $context, $payload) = @_;

                my %variants = (red => 42, green => 24, mauve => 19);

                return %variants;
            sub {
                my ($path, $context, $payload) = @_;

                # change paint to matt based on context
                $payload->{paint} = 'matt' if sum(@$context) > 20;

                my %variants = (circle => 10, square => 20);

                # add an extra triangular variant for mauve
                $variants{triangle} = 13 if grep { $_ eq 'mauve' } @$path;

                return %variants;
            sub {
                my ($path, $context, $payload) = @_;

                # skip all variants if path contains anything red or circular
                return if grep { $_ eq 'red' or $_ eq 'circle' } @$path;

                $payload->{spotty} = 1 if sum(@$context) > 35;

                my %variants = (small => 17, large => 92);

                return %variants;
            # ...
        [], # initial path
        [], # initial context
        { paint => 'gloss' }, # initial payload

The consumer code outputs:

    path: green/square/large    context: 24, 20, 92    payload: paint=>matt, spotty=>1
    path: green/square/small    context: 24, 20, 17    payload: paint=>matt, spotty=>1
    path: mauve/square/large    context: 19, 20, 92    payload: paint=>gloss, spotty=>1
    path: mauve/square/small    context: 19, 20, 17    payload: paint=>gloss, spotty=>1
    path: mauve/triangle/large  context: 19, 13, 92    payload: paint=>gloss
    path: mauve/triangle/small  context: 19, 13, 17    payload: paint=>gloss


NOTE: This is alpha code and liable to change while it and Test::WriteVariants mature.

The tumble() method calls a sequence of 'provider' code references each of which returns a hash. The first provider is called and then, for each hash item it returns, the tumble() method recurses to call the next provider.

The recursion continues until there are no more providers to call, at which point the consumer code reference is called. Effectively the providers create a tree of combinations and the consumer is called at the leafs of the tree.

If a provider returns no items then that part of the tree is pruned. Further providers, if any, are not called and the consumer is not called.

During a call to tumble() three values are passed down through the tree and into the consumer: path, context, and payload.

The path and context are derived from the names and values of the hashes returned by the providers. Typically the path define the current "path" through the tree of combinations.

The providers are passed the current path, context, and payload. The payload is cloned at each level of recursion so that any changes made to it by providers are only visible within the scope of the generated sub-tree.

Note that although the example above shows the path, context and payload as array references, the tumbler code makes no assumptions about them. They can be any kinds of values.

See Test::WriteVariants for a practical example use.



    $tumbler->consumer( sub { my ($path, $context, $payload) = @_; ... } );

Defines the code reference to call at the leafs of the generated tree of combinations. The default is to throw an exception.


    $tumbler->add_path( sub { my ($path, $name) = @_; return [ @$path, $name ] } )

Defines the code reference to call to create a new path value that combines the existing path and the new name. The default is shown in the example above.


    $tumbler->add_context( sub { my ($context, $value) = @_; return [ @$context, $value ] } )

Defines the code reference to call to create a new context value that combines the existing context and the new value. The default is shown in the example above.



Contructs new Data::Tumbler, deals with initial values for "ATTRIBUTES".


Tumbles providers to compute variants.


Please report any bugs or feature requests to bug-Data-Tumbler at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Data::Tumbler

You can also look for information at:


Tim Bunce, <timb at>


This module has been created to support DBI::Test in design and separation of concerns.


Copyright 2014-2015 Tim Bunce and Perl5 DBI Team.


This program is free software; you can redistribute it and/or modify it under the terms of either:

        a) the GNU General Public License as published by the Free
        Software Foundation; either version 1, or (at your option) any
        later version, or

        b) the "Artistic License" which comes with this Kit.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See either the GNU General Public License or the Artistic License for more details.