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```{index} single: CPAN::Meta::Merge
```

# CPAN::Meta::Merge

Merging CPAN Meta fragments

## VERSION

version 2.150013

## SYNOPSIS

```perl
my $merger = CPAN::Meta::Merge->new(default_version => "2");
my $meta = $merger->merge($base, @additional);
```

## DESCRIPTION

## METHODS

### new

This creates a CPAN::Meta::Merge object. It takes one mandatory named
argument, `version`, declaring the version of the meta-spec that must be
used for the merge. It can optionally take an `extra_mappings` argument
that allows one to add additional merging functions for specific elements.

The `extra_mappings` arguments takes a hash ref with the same type of
structure as described in [CPAN::Meta::Spec](Spec.md), except with its values as
one of the defined merge strategies or a code ref
to a merging function.

```perl
my $merger = CPAN::Meta::Merge->new(
    default_version => '2',
    extra_mappings => {
        'optional_features' => \&custom_merge_function,
        'x_custom' => 'set_addition',
        'x_meta_meta' => {
            name => 'identical',
            tags => 'set_addition',
        }
    }
);
```

### merge(@fragments)

Merge all `@fragments` together. It will accept both CPAN::Meta objects and
(possibly incomplete) hashrefs of metadata.

## MERGE STRATEGIES

`merge` uses various strategies to combine different elements of the CPAN::Meta objects.  The following strategies can be used with the extra\_mappings argument of `new`:

- identical

    The elements must be identical

- set\_addition

    The union of two array refs

    ```text
    [ a, b ] U [ a, c]  = [ a, b, c ]
    ```

- uniq\_map

    Key value pairs from the right hash are merged to the left hash.  Key
    collisions are only allowed if their values are the same.  This merge
    function will recurse into nested hash refs following the same merge
    rules.

- improvise

    This merge strategy will try to pick the appropriate predefined strategy
    based on what element type.  Array refs will try to use the
    `set_addition` strategy,  Hash refs will try to use the `uniq_map`
    strategy, and everything else will try the `identical` strategy.

## AUTHORS

- David Golden <dagolden@cpan.org>
- Ricardo Signes <cpan@semiotic.systems>
- Adam Kennedy <adamk@cpan.org>

## COPYRIGHT AND LICENSE

This software is copyright (c) 2010 by David Golden, Ricardo Signes, Adam Kennedy and Contributors.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.