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.