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## Providing default value for non-existing keys

<pm:Hash::WithDefault>


## Restricting keys

Perl through <pm:Hash::Util> (a core module) allows you to restrict what keys
can be set in a hash. This can be used to protect against typos and for simple
validation. (For more complex validation, e.g. allowing patterns of valid keys
and/or rejecting patterns of invalid keys, you can use the tie mechanism.)


## Reversing (inverting)

Reversing a hash (where keys become values and values become keys) can be done
using the builtin's `reverse` (which actually just reverse a list):

    %hash = (a=>1, b=>2);
    %reverse = reverse %hash; # => (2=>"b", 1=>"a")

Since the new keys can contain duplicates, this can "destroy" some old keys:

    %hash = (a=>1, b=>1);
    %reverse = reverse %hash; # => sometimes (1=>"b"), sometimes (1=>"a")

<pm:Hash::MoreUtil>'s `safe_reverse` allows you to specify a coderef that can
decide whether to ignore overwriting, croak, or whatever else.


## Slicing (creating subset)

<pm:Hash::MoreUtils>'s `slice_*` functions.

<pm:Hash::Subset>

<pm:Hash::Util::Pick>


## Tying

The tie mechanism, although relatively slow, allows you to create various kinds
of "magical" hash that does things whenever you get or set keys.


_
    'x.app.cpanmodules.show_entries' => 0,
};

Acme::CPANModulesUtil::Misc::populate_entries_from_module_links_in_description;

1;
# ABSTRACT: List of modules that manipulate hashes

__END__

=pod

=encoding UTF-8

=head1 NAME

Acme::CPANModules::HashUtilities - List of modules that manipulate hashes

=head1 VERSION

This document describes version 0.004 of Acme::CPANModules::HashUtilities (from Perl distribution Acme-CPANModules-HashUtilities), released on 2023-10-29.

=head1 DESCRIPTION

Most of the time, you don't need modules to manipulate hashes; Perl's built-in
facilities suffice. The modules below, however, are sometimes convenient. This
list is organized by task.

=head2 Creating an alias to another variable

L<Hash::Util>'s C<hv_store> allows you to store an alias to a variable in a
hash instead of copying the value. This means, if you set a hash value, it will
instead set the value of the aliased variable instead. Copying from Hash::Util's
documentation:

 my $sv = 0;
 hv_store(%hash,$key,$sv) or die "Failed to alias!";
 $hash{$key} = 1;
 print $sv; # prints 1

=head2 Getting internal information

Aside from creating restricted hash, L<Hash::Util> also provides routines to
get information about hash internals, e.g. C<hash_seed()>, C<hash_value()>,
C<bucket_info()>, C<bucket_stats()>, etc.

=head2 Merging

Merging hashes is usually as simple as:

 my %merged = (%hash1, %hash2, %hash3);

but sometimes you want different merging behavior, particularly in case where
the same key is found in more than one hash. See the various hash merging
modules:

L<Hash::Merge>

L<Data::ModeMerge>

L<Hash::Union>

=head2 Providing default value for non-existing keys

L<Hash::WithDefault>

=head2 Restricting keys

Perl through L<Hash::Util> (a core module) allows you to restrict what keys
can be set in a hash. This can be used to protect against typos and for simple
validation. (For more complex validation, e.g. allowing patterns of valid keys
and/or rejecting patterns of invalid keys, you can use the tie mechanism.)