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Author image chocolateboy

NAME

Hash::Fold - flatten and unflatten nested hashrefs

SYNOPSIS

    use Hash::Fold qw(flatten unflatten);

    my $object = bless { foo => 'bar' };

    my $nested = {
        foo => $object,
        baz => {
            a => 'b',
            c => [ 'd', { e => 'f' }, 42 ],
        },
    };

    my $flattened = flatten($nested);

    is_deeply $flattened, {
        'baz.a'     => 'b',
        'baz.c.0'   => 'd',
        'baz.c.1.e' => 'f',
        'baz.c.2'   => 42,
        'foo'       => $object,
    };

    my $roundtrip = unflatten($flattened);

    is_deeply $roundtrip, $nested;

DESCRIPTION

This module provides functional and OO interfaces which can be used to flatten, unflatten and merge nested hashrefs.

Unless noted, the functions listed below are also available as methods. Options provided to the Hash::Fold constructor can be supplied to the functions e.g.:

    use Hash::Fold;

    my $folder = Hash::Fold->new(delimiter => '/');

    $folder->fold($hash);

is equivalent to:

    use Hash::Fold qw(fold);

    my $folded = fold($hash, delimiter => '/');

Options (and constructor args) can be supplied as a list of key/value pairs or a hashref, so the following are equivalent:

    my $folded = fold($hash,   delimiter => '/'  );
    my $folded = fold($hash, { delimiter => '/' });

In addition, Hash::Fold uses Sub::Exporter, which allows functions to be imported with options baked in e.g.:

    use Hash::Fold fold => { delimiter => '/' };

    my $folded = fold($hash);

OPTIONS

As described above, the following options can be supplied as constructor args, import args, or per-function overrides. Under the hood, they are (Moo) attributes which can be wrapped and overridden like any other attributes.

array_delimiter

Type: Str, ro, default: "."

The delimiter prefixed to array elements when flattening and unflattening.

hash_delimiter

Type: Str, ro, default: "."

The delimiter prefixed to hash elements when flattening and unflattening.

delimiter

Type: Str

This is effectively a write-only attribute which assigns the same string to "array_delimiter" and "hash_delimiter". It can only be supplied as a constructor arg or function option (which are equivalent) i.e. Hash::Fold instances have no delimiter method.

on_cycle

Type: (Hash::Fold, Ref) -> None, ro

A callback invoked whenever "fold" encounters a circular reference i.e. a reference which contains itself as a nested value.

The callback is passed two arguments: the Hash::Fold instance and the value e.g.:

    sub on_cycle {
        my ($folder, $value) = @_;
        warn 'self-reference found: ', Dumper(value), $/;
    }

    my $folder = Hash::Fold->new(on_cycle => \&on_cycle);

Note that circular references are handled correctly i.e. they are treated as terminals and not traversed. This callback merely provides a mechanism to report them (e.g. by issuing a warning).

The default callback does nothing.

on_object

Type: (Hash::Fold, Ref) -> Any, ro

A callback invoked whenever "fold" encounters a value for which the "is_object" method returns true i.e. any reference that isn't an unblessed arrayref or unblessed hashref. This callback can be used to modify the value e.g. to return a traversable value (e.g. unblessed hashref) in place of a terminal (e.g. blessed hashref).

The callback is passed two arguments: the Hash::Fold instance and the object e.g.:

    use Scalar::Util qw(blessed);

    sub on_object {
        my ($folder, $value) = @_;

        if (blessed($value) && $value->isa('HASH')) {
            return { %$value }; # unbless
        } else {
            return $value;
        }
    }

    my $folder = Hash::Fold->new(on_object => \&on_object);

The default callback returns its value unchanged.

EXPORTS

Nothing by default. The following functions can be imported.

fold

Signature: (HashRef [, Hash|HashRef ]) -> HashRef

Takes a nested hashref and returns a single-level hashref with (by default) dotted keys. The delimiter can be overridden via the "delimiter", "array_delimiter" and "hash_delimiter" options.

Unblessed arrayrefs and unblessed hashrefs are traversed. All other values (e.g. strings, regexps, objects etc.) are treated as terminals and passed through verbatim, although this can be overridden by supplying a suitable "on_object" callback.

flatten

Signature: (HashRef [, Hash|HashRef ]) -> HashRef

Provided as an alias for "fold".

unfold

Signature: (HashRef [, Hash|HashRef ]) -> HashRef

Takes a flattened hashref and returns the corresponding nested hashref.

unflatten

Signature: (HashRef [, Hash|HashRef ]) -> HashRef

Provided as an alias for "unfold".

merge

Signature: (HashRef [, HashRef... ]) -> HashRef

Signature: (ArrayRef<HashRef> [, Hash|HashRef ]) -> HashRef

Takes a list of hashrefs which are then flattened, merged into one (in the order provided i.e. with precedence given to the rightmost arguments) and unflattened i.e. shorthand for:

    unflatten { map { %{ flatten $_ } } @_ }

To provide options to the merge subroutine, pass the hashrefs in an arrayref, and the options (as usual) as a list of key/value pairs or a hashref:

    merge([ $hash1, $hash2, ... ],   delimiter => ...  )
    merge([ $hash1, $hash2, ... ], { delimiter => ... })

METHODS

is_object

Signature: Any -> Bool

This method is called from "fold" to determine whether a value should be passed to the "on_object" callback.

It is passed each value encountered while traversing a hashref and returns true for all references (e.g. regexps, globs, objects etc.) apart from unblessed arrayrefs and unblessed hashrefs, and false for all other values (i.e. unblessed hashrefs, unblessed arrayrefs, and non-references).

ERRORS

Objects of the class Hash::Fold::Error are thrown upon error. The object stringifies to an error message with a strack trace.

Invalid Argument

If an input argument is not a hash, an error object will be thrown with the type attribute set to the unexpected type of the argument.

Incompatible path component

If, during the course of an "unfold"/"unflatten" or a "merge", incompatible types are found along the same paths in the structures, an error object will be thrown with the path attribute set to the path with the incorrect type, and the type attribute set to the unexpected type. For example, the following paths would be incompatible:

   foo.0 = 2
   foo = 3

- as foo cannot be both a scalar and an array.

VERSION

1.0.0

SEE ALSO

AUTHOR

  • chocolateboy <chocolate@cpan.org>

  • djerius <djerius@cpan.org>

COPYRIGHT

Copyright (c) 2014-2019 by chocolateboy.

This is free software; you can redistribute it and/or modify it under the terms of the Artistic License 2.0.