package Hash::Util; require 5.007003; use strict; use Carp; require Exporter; our @ISA = qw(Exporter); our @EXPORT_OK = qw(lock_keys unlock_keys lock_value unlock_value lock_hash unlock_hash hash_seed ); our $VERSION = 0.05; =head1 NAME Hash::Util - A selection of general-utility hash subroutines =head1 SYNOPSIS use Hash::Util qw(lock_keys unlock_keys lock_value unlock_value lock_hash unlock_hash hash_seed); %hash = (foo => 42, bar => 23); lock_keys(%hash); lock_keys(%hash, @keyset); unlock_keys(%hash); lock_value (%hash, 'foo'); unlock_value(%hash, 'foo'); lock_hash (%hash); unlock_hash(%hash); my $hashes_are_randomised = hash_seed() != 0; =head1 DESCRIPTION C contains special functions for manipulating hashes that don't really warrant a keyword. By default C does not export anything. =head2 Restricted hashes 5.8.0 introduces the ability to restrict a hash to a certain set of keys. No keys outside of this set can be added. It also introduces the ability to lock an individual key so it cannot be deleted and the value cannot be changed. This is intended to largely replace the deprecated pseudo-hashes. =over 4 =item lock_keys =item unlock_keys lock_keys(%hash); lock_keys(%hash, @keys); Restricts the given %hash's set of keys to @keys. If @keys is not given it restricts it to its current keyset. No more keys can be added. delete() and exists() will still work, but will not alter the set of allowed keys. B: the current implementation prevents the hash from being bless()ed while it is in a locked state. Any attempt to do so will raise an exception. Of course you can still bless() the hash before you call lock_keys() so this shouldn't be a problem. unlock_keys(%hash); Removes the restriction on the %hash's keyset. =cut sub lock_keys (\%;@) { my($hash, @keys) = @_; Internals::hv_clear_placeholders %$hash; if( @keys ) { my %keys = map { ($_ => 1) } @keys; my %original_keys = map { ($_ => 1) } keys %$hash; foreach my $k (keys %original_keys) { die sprintf "Hash has key '$k' which is not in the new key ". "set at %s line %d\n", (caller)[1,2] unless $keys{$k}; } foreach my $k (@keys) { $hash->{$k} = undef unless exists $hash->{$k}; } Internals::SvREADONLY %$hash, 1; foreach my $k (@keys) { delete $hash->{$k} unless $original_keys{$k}; } } else { Internals::SvREADONLY %$hash, 1; } return; } sub unlock_keys (\%) { my($hash) = shift; Internals::SvREADONLY %$hash, 0; return; } =item lock_value =item unlock_value lock_value (%hash, $key); unlock_value(%hash, $key); Locks and unlocks an individual key of a hash. The value of a locked key cannot be changed. %hash must have already been locked for this to have useful effect. =cut sub lock_value (\%$) { my($hash, $key) = @_; carp "Cannot usefully lock values in an unlocked hash" unless Internals::SvREADONLY %$hash; Internals::SvREADONLY $hash->{$key}, 1; } sub unlock_value (\%$) { my($hash, $key) = @_; Internals::SvREADONLY $hash->{$key}, 0; } =item B =item B lock_hash(%hash); lock_hash() locks an entire hash, making all keys and values readonly. No value can be changed, no keys can be added or deleted. unlock_hash(%hash); unlock_hash() does the opposite of lock_hash(). All keys and values are made read/write. All values can be changed and keys can be added and deleted. =cut sub lock_hash (\%) { my($hash) = shift; lock_keys(%$hash); foreach my $key (keys %$hash) { lock_value(%$hash, $key); } return 1; } sub unlock_hash (\%) { my($hash) = shift; foreach my $key (keys %$hash) { unlock_value(%$hash, $key); } unlock_keys(%$hash); return 1; } =item B my $hash_seed = hash_seed(); hash_seed() returns the seed number used to randomise hash ordering. Zero means the "traditional" random hash ordering, non-zero means the new even more random hash ordering introduced in Perl 5.8.1. B: by knowing it one can craft a denial-of-service attack against Perl code, even remotely, see L for more information. B to people who don't need to know it. See also L. =cut sub hash_seed () { Internals::rehash_seed(); } =back =head1 CAVEATS Note that the trapping of the restricted operations is not atomic: for example eval { %hash = (illegal_key => 1) } leaves the C<%hash> empty rather than with its original contents. =head1 AUTHOR Michael G Schwern on top of code by Nick Ing-Simmons and Jeffrey Friedl. =head1 SEE ALSO L, L, L, and L. =cut 1;