tools/perl-5.8.0/man/man3/Hash::Util.3

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.\" ========================================================================
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.IX Title "Hash::Util 3"
.TH Hash::Util 3 "2002-06-01" "perl v5.8.0" "Perl Programmers Reference Guide"
.SH "NAME"
Hash::Util \- A selection of general\-utility hash subroutines
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 3
\&  use Hash::Util qw(lock_keys   unlock_keys
\&                    lock_value  unlock_value
\&                    lock_hash   unlock_hash);
.Ve
.PP
.Vb 4
\&  %hash = (foo => 42, bar => 23);
\&  lock_keys(%hash);
\&  lock_keys(%hash, @keyset);
\&  unlock_keys(%hash);
.Ve
.PP
.Vb 2
\&  lock_value  (%hash, 'foo');
\&  unlock_value(%hash, 'foo');
.Ve
.PP
.Vb 2
\&  lock_hash  (%hash);
\&  unlock_hash(%hash);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`Hash::Util\*(C'\fR contains special functions for manipulating hashes that
don't really warrant a keyword.
.PP
By default \f(CW\*(C`Hash::Util\*(C'\fR does not export anything.
.Sh "Restricted hashes"
.IX Subsection "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.
.PP
This is intended to largely replace the deprecated pseudo\-hashes.
.IP "lock_keys" 4
.IX Item "lock_keys"
.PD 0
.IP "unlock_keys" 4
.IX Item "unlock_keys"
.PD
.Vb 2
\&  lock_keys(%hash);
\&  lock_keys(%hash, @keys);
.Ve
.Sp
Restricts the given \f(CW%hash\fR's set of keys to \f(CW@keys\fR.  If \f(CW@keys\fR is not
given it restricts it to its current keyset.  No more keys can be
added.  \fIdelete()\fR and \fIexists()\fR will still work, but it does not effect
the set of allowed keys.
.Sp
.Vb 1
\&  unlock_keys(%hash;)
.Ve
.Sp
Removes the restriction on the \f(CW%hash\fR's keyset.
.IP "lock_value" 4
.IX Item "lock_value"
.PD 0
.IP "unlock_value" 4
.IX Item "unlock_value"
.PD
.Vb 2
\&  lock_key  (%hash, $key);
\&  unlock_key(%hash, $key);
.Ve
.Sp
Locks and unlocks an individual key of a hash.  The value of a locked
key cannot be changed.
.Sp
%hash must have already been locked for this to have useful effect.
.IP "\fBlock_hash\fR" 4
.IX Item "lock_hash"
.PD 0
.IP "\fBunlock_hash\fR" 4
.IX Item "unlock_hash"
.PD
.Vb 1
\&    lock_hash(%hash);
.Ve
.Sp
\&\fIlock_hash()\fR locks an entire hash, making all keys and values readonly.
No value can be changed, no keys can be added or deleted.
.Sp
.Vb 1
\&    unlock_hash(%hash);
.Ve
.Sp
\&\fIunlock_hash()\fR does the opposite of \fIlock_hash()\fR.  All keys and values
are made read/write.  All values can be changed and keys can be added
and deleted.
.SH "AUTHOR"
.IX Header "AUTHOR"
Michael G Schwern <schwern@pobox.com> on top of code by Nick
Ing-Simmons and Jeffrey Friedl.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Scalar::Util, List::Util, Hash::Util