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.