NAME

       Hash::StoredIterator - Functions for accessing a hashes internal iterator.

DESCRIPTION

       In perl all hashes have an internal iterator. This iterator is used by the "each()"
       function, as well as by "keys()" and "values()". Because these all share use of the same
       iterator, they tend to interact badly with eachother when nested.

       Hash::StoredIterator gives you access to get, set, and init the iterator inside a hash.
       This allows you to store the current iterator, use each/keys/values/etc, and then restore
       the iterator, this helps you to ensure you do not interact badly with other users of the
       iterator.

       Along with low-level get/set/init functions, there are also 2 variations of "each()" which
       let you act upon each key/value pair in a safer way than vanilla "each()"

       This module can also export new implementations of "keys()" and "values()" which stash and
       restore the iterator so that they are safe to use within "each()".

SYNOPSIS

           use Hash::StoredIterator qw{
               hmap
               hkeys
               hvalues
               iterator
               hash_get_iterator
               hash_set_iterator
               hash_init_iterator
           };

           my %hash = map { $_ => uc( $_ )} 'a' .. 'z';

           my @keys = hkeys %hash;
           my @values = hvalues %hash;

       Each section below is functionally identical.

           my $iterator = iterator %hash;
           while( my ( $k, $v ) = $i->() ) {
               print "$k: $value\n";
           }

           hmap { print "$a: $b\n" } %hash;

           hamp { print "$_: $b\n" } %hash;

           hmap {
               my ( $key, $val ) = @_;
               print "$key: $val\n";
           } %hash;

       It is safe to nest calls to "hmap()", "iterator()", "hkeys()", and "hvalues()"

           hmap {
               my ( $key, $val ) = @_;
               print "$key: $val\n";
               my @keys = hkeys( %hash );
           } %hash;

       "hmap()" and "iterator()" will also properly handle calls to "CORE::each", "CORE::keys",
       and "Core::values" nested within them.

           hmap {
               my ( $key, $val ) = @_;
               print "$key: $val\n";

               # No infinite loop!
               my @keys = keys %hash;
           } %hash;

       Low Level:

           hash_init_iterator( \%hash );
           my $iter = hash_get_iterator( \%hash );
           # NOTE: Never manually specify an $iter value, ALWAYS use a value from
           # hash_get_iterator.
           hash_set_iterator( \%hash, $iter );

EXPORTS

       my $i = iterator %hash
           Get an iterator that can be used to retrieve key/value pairs.

               my $i = iterator %hash;
               while( my ($k, $v) = $i->() ) {
                   ...
               }

           The iterator is a coderef, so you call it like this: "$i-"()>. You can also use the
           sub anywhere you would use any other coderef.

       hmap( \&callback, %hash )
       hmap { ... } %hash
           Iterate each key/pair calling "$callback-"( $key, $value )> for each set. In addition
           $a and $_ are set to the key, and $b is set to the value.  This is done primarily for
           convenience of matching against the key, and short callbacks that will be cluttered by
           parsing @_ noise.

           Note: See caveats.

       my @keys = hkeys( %hash )
           Same as the builtin "keys()", except it stores and restores the iterator.

           Note: Overriding the builtin keys(), even locally, causes stange interactions with
           other builtins. When trying to export hkeys as keys, a call to "sort keys %hash" would
           cause undef to be passed into keys() as the first and only argument.

       my @values = hvalues( %hash )
           Same as the builtin "values()", except it stores and restores the iterator.

           Note: Overriding the builtin values(), even locally, causes stange interactions with
           other builtins. When trying to export hvalues as values, a call to "sort values %hash"
           would cause undef to be passed into values() as the first and only argument.

       my $i = hash_get_iterator( \%hash )
           Get the current iterator value.

       hash_set_iterator( \%hash, $i )
           Set the iterator value.

           Note: Only ever set this to the value retrieved by "hash_get_iterator()", setting the
           iterator in any other way is untested, and may result in undefined behavior.

       hash_init_iterator( \%hash )
           Initialize or reset the hash iterator.

DEPRECATED

       These have been deprecated because they were terrible names. eich was also deprecated
       because it was unnatural to use.

       eich
           use iterator() instead

       eech
           use hmap instead

CAVEATS

       Modification of hash during iteration
           Just like with the builtin "each()" modifying the hash between calls to each is not
           recommended and can result in undefined behavior. The builtin "each()" does allow for
           deleting the iterations key, however that is NOT supported by this library.

       sort() edge case
           For some reason "[sort hkeys %hash]" and "[sort hkeys(%hash)]" both result in a list
           that has all the keys and values (and strangly not in sorted order).  However
           "[sort(hkeys(%hash))]" works fine.

AUTHORS

       Chad Granum exodist7@gmail.com

COPYRIGHT

       Copyright (C) 2013 Chad Granum

       Hash-StoredIterator is free software; Standard perl licence.

       Hash-StoredIterator 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 the license for more details.