NAME
Hash::Util - A selection of general-utility hash subroutines
SYNOPSIS
use Hash::Util qw(lockkeys unlockkeys
lockvalue unlockvalue lockhash unlockhash hashseed);%hash = (foo => 42, bar => 23);
lockkeys(%hash);
lockkeys(%hash, @keyset);
unlockkeys(%hash);
lockvalue (%hash, 'foo');
unlockvalue(%hash, 'foo');
lockhash (%hash);
unlockhash(%hash);
my $hashesarerandomised = hashseed() != 0;
DESCRIPTION
"Hash::Util" contains special functions for manipulating hashes that
don't really warrant a keyword.By default "Hash::Util" does not export anything.
RReessttrriicctteedd hhaasshheess 5.8.0 introduces the ability to restrict a hash to a certain set of keys. No keys outside of this set can be added. It also introduces the ability to lock an individual key so it cannot be deleted and the value cannot be changed.This is intended to largely replace the deprecated pseudo-hashes.
lockkeys unlockkeyslockkeys(%hash);
lockkeys(%hash, @keys);
Restricts the given %hash's set of keys to @keys. If @keys is not
given it restricts it to its current keyset. No more keys can be added. delete() and exists() will still work, but will not alter the set of allowed keys. NNoottee: the current implementation prevents the hash from being bless()ed while it is in a locked state. Any attempt to do so will raise an exception. Of course you can still bless() the hash before you call lockkeys() so this shouldn't be a problem.unlockkeys(%hash);
Removes the restriction on the %hash's keyset.
lockvalue unlockvaluelockvalue (%hash, $key);
unlockvalue(%hash, $key);
Locks and unlocks an individual key of a hash. The value of a locked key cannot be changed.%hash must have already been locked for this to have useful effect.
lloocckkhhaasshh uunnlloocckkhhaasshhlockhash(%hash);
lockhash() locks an entire hash, making all keys and values read-
only. No value can be changed, no keys can be added or deleted.unlockhash(%hash);
unlockhash() does the opposite of lockhash(). All keys and val-
ues are made read/write. All values can be changed and keys can be added and deleted. hhaasshhsseeeeddmy $hashseed = hashseed();
hashseed() returns the seed number used to randomise hash order-
ing. Zero means the "traditional" random hash ordering, non-zero
means the new even more random hash ordering introduced in Perl 5.8.1. NNoottee tthhaatt tthhee hhaasshh sseeeedd iiss sseennssiittiivvee iinnffoorrmmaattiioonn: by knowing it onecan craft a denial-of-service attack against Perl code, even
remotely, see "Algorithmic Complexity Attacks" in perlsec for more information. DDoo nnoott ddiisscclloossee tthhee hhaasshh sseeeedd to people who don't need to know it. See also "PERLHASHSEEDDEBUG" in perlrun. CCAAVVEEAATTSS Note that the trapping of the restricted operations is not atomic: for exampleeval { %hash = (illegalkey => 1) }
leaves the %hash empty rather than with its original contents.
AUTHORMichael G Schwern
mons and Jeffrey Friedl.on top of code by Nick Ing-Sim- SEE ALSO
Scalar::Util, List::Util, Hash::Util, and "Algorithmic Complexity
Attacks" in perlsec.perl v5.8.8 2001-09-21 Hash::Util(3pm)