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{ eich eech hkeys hvalues 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; while( my ( $k, $v ) = eich( %hash, $iterator )) { print "$k: $value\n"; } eech { print "$a: $b\n" } %hash; eech { print "$_: $b\n" } %hash; eech { my ( $key, $val ) = @_; print "$key: $val\n"; } %hash; It is safe to nest calls to "eich()", "eech()", "hkeys()", and "hvalues()" eech { my ( $key, $val ) = @_; print "$key: $val\n"; my @keys = hkeys( %hash ); } %hash; "eech()" and "eich()" will also properly handle calls to "CORE::each", "CORE::keys", and "Core::values" nested within them. eech { 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 ( $key, $val ) = eich( %hash, $iterator ) This is just like "each()", except that you need to give it a scalar in which the iterator will be stored. If the $iterator value is undefined, the iterator will be initialized, so on the first call it should be undef. Never set the value of $iterator directly! The behavior of doing so is undefined, it might work, it might not, it might do bad things. Note: See caveats. eech( \&callback, %hash ) eech { ... } %hash Iterate each key/pair calling "$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. 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.