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1#
2# Copyright (c) 1995-2000, Raphael Manfredi
3#
4# You may redistribute only under the same terms as Perl 5, as specified
5# in the README file that comes with the distribution.
6#
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7
8require DynaLoader;
9require Exporter;
10package Storable; @ISA = qw(Exporter DynaLoader);
11
12@EXPORT = qw(store retrieve);
13@EXPORT_OK = qw(
9e21b3d0 14 nstore store_fd nstore_fd fd_retrieve
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15 freeze nfreeze thaw
16 dclone
9e21b3d0 17 retrieve_fd
dd19458b 18 lock_store lock_nstore lock_retrieve
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19);
20
21use AutoLoader;
01d7b99e 22use vars qw($canonical $forgive_me $VERSION);
7a6a85bf 23
2fc01f5f 24$VERSION = '2.15_02';
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25*AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr...
26
27#
28# Use of Log::Agent is optional
29#
30
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31{
32 local $SIG{__DIE__};
33 eval "use Log::Agent";
34}
7a6a85bf 35
530b72ba 36require Carp;
7a6a85bf 37
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38#
39# They might miss :flock in Fcntl
40#
41
42BEGIN {
596596d5 43 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {
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44 Fcntl->import(':flock');
45 } else {
46 eval q{
47 sub LOCK_SH () {1}
48 sub LOCK_EX () {2}
49 };
50 }
51}
52
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53sub CLONE {
54 # clone context under threads
55 Storable::init_perinterp();
56}
57
b8778c7c 58# Can't Autoload cleanly as this clashes 8.3 with &retrieve
9e21b3d0 59sub retrieve_fd { &fd_retrieve } # Backward compatibility
cb3d9de5 60
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61# By default restricted hashes are downgraded on earlier perls.
62
63$Storable::downgrade_restricted = 1;
e8189732 64$Storable::accept_future_minor = 1;
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65bootstrap Storable;
661;
67__END__
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68#
69# Use of Log::Agent is optional. If it hasn't imported these subs then
70# Autoloader will kindly supply our fallback implementation.
71#
72
73sub logcroak {
74 Carp::croak(@_);
75}
76
77sub logcarp {
78 Carp::carp(@_);
79}
b8778c7c 80
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81#
82# Determine whether locking is possible, but only when needed.
83#
84
530b72ba 85sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
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86 return $CAN_FLOCK if defined $CAN_FLOCK;
87 require Config; import Config;
88 return $CAN_FLOCK =
89 $Config{'d_flock'} ||
90 $Config{'d_fcntl_can_lock'} ||
91 $Config{'d_lockf'};
92}
93
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94sub show_file_magic {
95 print <<EOM;
96#
97# To recognize the data files of the Perl module Storable,
98# the following lines need to be added to the local magic(5) file,
99# usually either /usr/share/misc/magic or /etc/magic.
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100#
1010 string perl-store perl Storable(v0.6) data
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102>4 byte >0 (net-order %d)
103>>4 byte &01 (network-ordered)
104>>4 byte =3 (major 1)
105>>4 byte =2 (major 1)
106
0a0da639 1070 string pst0 perl Storable(v0.7) data
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108>4 byte >0
109>>4 byte &01 (network-ordered)
110>>4 byte =5 (major 2)
111>>4 byte =4 (major 2)
112>>5 byte >0 (minor %d)
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113EOM
114}
115
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116sub read_magic {
117 my $header = shift;
118 return unless defined $header and length $header > 11;
119 my $result;
120 if ($header =~ s/^perl-store//) {
121 die "Can't deal with version 0 headers";
122 } elsif ($header =~ s/^pst0//) {
123 $result->{file} = 1;
124 }
125 # Assume it's a string.
126 my ($major, $minor, $bytelen) = unpack "C3", $header;
127
128 my $net_order = $major & 1;
129 $major >>= 1;
130 @$result{qw(major minor netorder)} = ($major, $minor, $net_order);
131
132 return $result if $net_order;
133
134 # I assume that it is rare to find v1 files, so this is an intentionally
135 # inefficient way of doing it, to make the rest of the code constant.
136 if ($major < 2) {
137 delete $result->{minor};
138 $header = '.' . $header;
139 $bytelen = $minor;
140 }
141
142 @$result{qw(byteorder intsize longsize ptrsize)} =
143 unpack "x3 A$bytelen C3", $header;
144
145 if ($major >= 2 and $minor >= 2) {
146 $result->{nvsize} = unpack "x6 x$bytelen C", $header;
147 }
148 $result;
149}
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150
151#
152# store
153#
154# Store target object hierarchy, identified by a reference to its root.
155# The stored object tree may later be retrieved to memory via retrieve.
156# Returns undef if an I/O error occurred, in which case the file is
157# removed.
158#
159sub store {
dd19458b 160 return _store(\&pstore, @_, 0);
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161}
162
163#
164# nstore
165#
166# Same as store, but in network order.
167#
168sub nstore {
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169 return _store(\&net_pstore, @_, 0);
170}
171
172#
173# lock_store
174#
175# Same as store, but flock the file first (advisory locking).
176#
177sub lock_store {
178 return _store(\&pstore, @_, 1);
179}
180
181#
182# lock_nstore
183#
184# Same as nstore, but flock the file first (advisory locking).
185#
186sub lock_nstore {
187 return _store(\&net_pstore, @_, 1);
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188}
189
190# Internal store to file routine
191sub _store {
192 my $xsptr = shift;
193 my $self = shift;
dd19458b 194 my ($file, $use_locking) = @_;
7a6a85bf 195 logcroak "not a reference" unless ref($self);
b12202d0 196 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
7a6a85bf 197 local *FILE;
dd19458b 198 if ($use_locking) {
6e0ac6f5 199 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
862382c7 200 unless (&CAN_FLOCK) {
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201 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
202 return undef;
f567092b 203 }
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204 flock(FILE, LOCK_EX) ||
205 logcroak "can't get exclusive lock on $file: $!";
206 truncate FILE, 0;
207 # Unlocking will happen when FILE is closed
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208 } else {
209 open(FILE, ">$file") || logcroak "can't create $file: $!";
dd19458b 210 }
6e0ac6f5 211 binmode FILE; # Archaic systems...
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212 my $da = $@; # Don't mess if called from exception handler
213 my $ret;
214 # Call C routine nstore or pstore, depending on network order
215 eval { $ret = &$xsptr(*FILE, $self) };
216 close(FILE) or $ret = undef;
217 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
218 logcroak $@ if $@ =~ s/\.?\n$/,/;
219 $@ = $da;
220 return $ret ? $ret : undef;
221}
222
223#
224# store_fd
225#
226# Same as store, but perform on an already opened file descriptor instead.
227# Returns undef if an I/O error occurred.
228#
229sub store_fd {
230 return _store_fd(\&pstore, @_);
231}
232
233#
234# nstore_fd
235#
236# Same as store_fd, but in network order.
237#
238sub nstore_fd {
239 my ($self, $file) = @_;
240 return _store_fd(\&net_pstore, @_);
241}
242
243# Internal store routine on opened file descriptor
244sub _store_fd {
245 my $xsptr = shift;
246 my $self = shift;
247 my ($file) = @_;
248 logcroak "not a reference" unless ref($self);
249 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
250 my $fd = fileno($file);
251 logcroak "not a valid file descriptor" unless defined $fd;
252 my $da = $@; # Don't mess if called from exception handler
253 my $ret;
254 # Call C routine nstore or pstore, depending on network order
255 eval { $ret = &$xsptr($file, $self) };
256 logcroak $@ if $@ =~ s/\.?\n$/,/;
596596d5 257 local $\; print $file ''; # Autoflush the file if wanted
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258 $@ = $da;
259 return $ret ? $ret : undef;
260}
261
262#
263# freeze
264#
265# Store oject and its hierarchy in memory and return a scalar
266# containing the result.
267#
268sub freeze {
269 _freeze(\&mstore, @_);
270}
271
272#
273# nfreeze
274#
275# Same as freeze but in network order.
276#
277sub nfreeze {
278 _freeze(\&net_mstore, @_);
279}
280
281# Internal freeze routine
282sub _freeze {
283 my $xsptr = shift;
284 my $self = shift;
285 logcroak "not a reference" unless ref($self);
286 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
287 my $da = $@; # Don't mess if called from exception handler
288 my $ret;
289 # Call C routine mstore or net_mstore, depending on network order
290 eval { $ret = &$xsptr($self) };
291 logcroak $@ if $@ =~ s/\.?\n$/,/;
292 $@ = $da;
293 return $ret ? $ret : undef;
294}
295
296#
297# retrieve
298#
299# Retrieve object hierarchy from disk, returning a reference to the root
300# object of that tree.
301#
302sub retrieve {
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303 _retrieve($_[0], 0);
304}
305
306#
307# lock_retrieve
308#
309# Same as retrieve, but with advisory locking.
310#
311sub lock_retrieve {
312 _retrieve($_[0], 1);
313}
314
315# Internal retrieve routine
316sub _retrieve {
317 my ($file, $use_locking) = @_;
7a6a85bf 318 local *FILE;
dd19458b 319 open(FILE, $file) || logcroak "can't open $file: $!";
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320 binmode FILE; # Archaic systems...
321 my $self;
322 my $da = $@; # Could be from exception handler
dd19458b 323 if ($use_locking) {
862382c7 324 unless (&CAN_FLOCK) {
8be2b38b 325 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
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326 return undef;
327 }
8be2b38b 328 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
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329 # Unlocking will happen when FILE is closed
330 }
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331 eval { $self = pretrieve(*FILE) }; # Call C routine
332 close(FILE);
333 logcroak $@ if $@ =~ s/\.?\n$/,/;
334 $@ = $da;
335 return $self;
336}
337
338#
9e21b3d0 339# fd_retrieve
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340#
341# Same as retrieve, but perform from an already opened file descriptor instead.
342#
9e21b3d0 343sub fd_retrieve {
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344 my ($file) = @_;
345 my $fd = fileno($file);
346 logcroak "not a valid file descriptor" unless defined $fd;
347 my $self;
348 my $da = $@; # Could be from exception handler
349 eval { $self = pretrieve($file) }; # Call C routine
350 logcroak $@ if $@ =~ s/\.?\n$/,/;
351 $@ = $da;
352 return $self;
353}
354
355#
356# thaw
357#
358# Recreate objects in memory from an existing frozen image created
359# by freeze. If the frozen image passed is undef, return undef.
360#
361sub thaw {
362 my ($frozen) = @_;
363 return undef unless defined $frozen;
364 my $self;
365 my $da = $@; # Could be from exception handler
366 eval { $self = mretrieve($frozen) }; # Call C routine
367 logcroak $@ if $@ =~ s/\.?\n$/,/;
368 $@ = $da;
369 return $self;
370}
371
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3721;
373__END__
374
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375=head1 NAME
376
f062ea6c 377Storable - persistence for Perl data structures
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378
379=head1 SYNOPSIS
380
381 use Storable;
382 store \%table, 'file';
383 $hashref = retrieve('file');
384
385 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
386
387 # Network order
388 nstore \%table, 'file';
389 $hashref = retrieve('file'); # There is NO nretrieve()
390
391 # Storing to and retrieving from an already opened file
392 store_fd \@array, \*STDOUT;
393 nstore_fd \%table, \*STDOUT;
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394 $aryref = fd_retrieve(\*SOCKET);
395 $hashref = fd_retrieve(\*SOCKET);
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396
397 # Serializing to memory
398 $serialized = freeze \%table;
399 %table_clone = %{ thaw($serialized) };
400
401 # Deep (recursive) cloning
402 $cloneref = dclone($ref);
403
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404 # Advisory locking
405 use Storable qw(lock_store lock_nstore lock_retrieve)
406 lock_store \%table, 'file';
407 lock_nstore \%table, 'file';
408 $hashref = lock_retrieve('file');
409
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410=head1 DESCRIPTION
411
f062ea6c 412The Storable package brings persistence to your Perl data structures
7a6a85bf 413containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
c261f00e 414conveniently stored to disk and retrieved at a later time.
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415
416It can be used in the regular procedural way by calling C<store> with
417a reference to the object to be stored, along with the file name where
418the image should be written.
775ecd75 419
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420The routine returns C<undef> for I/O problems or other internal error,
421a true value otherwise. Serious errors are propagated as a C<die> exception.
422
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423To retrieve data stored to disk, use C<retrieve> with a file name.
424The objects stored into that file are recreated into memory for you,
425and a I<reference> to the root object is returned. In case an I/O error
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426occurs while reading, C<undef> is returned instead. Other serious
427errors are propagated via C<die>.
428
429Since storage is performed recursively, you might want to stuff references
430to objects that share a lot of common data into a single array or hash
431table, and then store that object. That way, when you retrieve back the
432whole thing, the objects will continue to share what they originally shared.
433
434At the cost of a slight header overhead, you may store to an already
435opened file descriptor using the C<store_fd> routine, and retrieve
9e21b3d0 436from a file via C<fd_retrieve>. Those names aren't imported by default,
c261f00e 437so you will have to do that explicitly if you need those routines.
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438The file descriptor you supply must be already opened, for read
439if you're going to retrieve and for write if you wish to store.
440
441 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
9e21b3d0 442 $hashref = fd_retrieve(*STDIN);
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443
444You can also store data in network order to allow easy sharing across
445multiple platforms, or when storing on a socket known to be remotely
446connected. The routines to call have an initial C<n> prefix for I<network>,
447as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
448correctly restored so you don't have to know whether you're restoring
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449from native or network ordered data. Double values are stored stringified
450to ensure portability as well, at the slight risk of loosing some precision
451in the last decimals.
7a6a85bf 452
9e21b3d0 453When using C<fd_retrieve>, objects are retrieved in sequence, one
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454object (i.e. one recursive tree) per associated C<store_fd>.
455
456If you're more from the object-oriented camp, you can inherit from
457Storable and directly store your objects by invoking C<store> as
458a method. The fact that the root of the to-be-stored tree is a
459blessed reference (i.e. an object) is special-cased so that the
460retrieve does not provide a reference to that object but rather the
461blessed object reference itself. (Otherwise, you'd get a reference
462to that blessed object).
463
464=head1 MEMORY STORE
465
466The Storable engine can also store data into a Perl scalar instead, to
467later retrieve them. This is mainly used to freeze a complex structure in
468some safe compact memory place (where it can possibly be sent to another
469process via some IPC, since freezing the structure also serializes it in
470effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
471out and recreate the original complex structure in memory.
472
473Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
474If you wish to send out the frozen scalar to another machine, use
475C<nfreeze> instead to get a portable image.
476
477Note that freezing an object structure and immediately thawing it
478actually achieves a deep cloning of that structure:
479
480 dclone(.) = thaw(freeze(.))
481
482Storable provides you with a C<dclone> interface which does not create
483that intermediary scalar but instead freezes the structure in some
c261f00e 484internal memory space and then immediately thaws it out.
7a6a85bf 485
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486=head1 ADVISORY LOCKING
487
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488The C<lock_store> and C<lock_nstore> routine are equivalent to
489C<store> and C<nstore>, except that they get an exclusive lock on
490the file before writing. Likewise, C<lock_retrieve> does the same
491as C<retrieve>, but also gets a shared lock on the file before reading.
dd19458b 492
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493As with any advisory locking scheme, the protection only works if you
494systematically use C<lock_store> and C<lock_retrieve>. If one side of
495your application uses C<store> whilst the other uses C<lock_retrieve>,
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496you will get no protection at all.
497
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498The internal advisory locking is implemented using Perl's flock()
499routine. If your system does not support any form of flock(), or if
500you share your files across NFS, you might wish to use other forms
501of locking by using modules such as LockFile::Simple which lock a
502file using a filesystem entry, instead of locking the file descriptor.
dd19458b 503
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504=head1 SPEED
505
506The heart of Storable is written in C for decent speed. Extra low-level
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507optimizations have been made when manipulating perl internals, to
508sacrifice encapsulation for the benefit of greater speed.
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509
510=head1 CANONICAL REPRESENTATION
511
f062ea6c 512Normally, Storable stores elements of hashes in the order they are
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513stored internally by Perl, i.e. pseudo-randomly. If you set
514C<$Storable::canonical> to some C<TRUE> value, Storable will store
515hashes with the elements sorted by their key. This allows you to
516compare data structures by comparing their frozen representations (or
517even the compressed frozen representations), which can be useful for
518creating lookup tables for complicated queries.
519
f062ea6c 520Canonical order does not imply network order; those are two orthogonal
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521settings.
522
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523=head1 CODE REFERENCES
524
525Since Storable version 2.05, CODE references may be serialized with
526the help of L<B::Deparse>. To enable this feature, set
3c4b39be 527C<$Storable::Deparse> to a true value. To enable deserialization,
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528C<$Storable::Eval> should be set to a true value. Be aware that
529deserialization is done through C<eval>, which is dangerous if the
530Storable file contains malicious data. You can set C<$Storable::Eval>
531to a subroutine reference which would be used instead of C<eval>. See
532below for an example using a L<Safe> compartment for deserialization
533of CODE references.
534
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535If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false
536values, then the value of C<$Storable::forgive_me> (see below) is
537respected while serializing and deserializing.
538
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539=head1 FORWARD COMPATIBILITY
540
541This release of Storable can be used on a newer version of Perl to
f062ea6c 542serialize data which is not supported by earlier Perls. By default,
c261f00e 543Storable will attempt to do the right thing, by C<croak()>ing if it
775ecd75 544encounters data that it cannot deserialize. However, the defaults
f062ea6c 545can be changed as follows:
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546
547=over 4
548
549=item utf8 data
550
551Perl 5.6 added support for Unicode characters with code points > 255,
552and Perl 5.8 has full support for Unicode characters in hash keys.
553Perl internally encodes strings with these characters using utf8, and
554Storable serializes them as utf8. By default, if an older version of
555Perl encounters a utf8 value it cannot represent, it will C<croak()>.
556To change this behaviour so that Storable deserializes utf8 encoded
557values as the string of bytes (effectively dropping the I<is_utf8> flag)
558set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
559data loss, because with C<$drop_utf8> true, it becomes impossible to tell
560whether the original data was the Unicode string, or a series of bytes
561that happen to be valid utf8.
562
563=item restricted hashes
564
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565Perl 5.8 adds support for restricted hashes, which have keys
566restricted to a given set, and can have values locked to be read only.
567By default, when Storable encounters a restricted hash on a perl
568that doesn't support them, it will deserialize it as a normal hash,
569silently discarding any placeholder keys and leaving the keys and
570all values unlocked. To make Storable C<croak()> instead, set
571C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore
572the default set it back to some C<TRUE> value.
c261f00e 573
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574=item files from future versions of Storable
575
576Earlier versions of Storable would immediately croak if they encountered
577a file with a higher internal version number than the reading Storable
578knew about. Internal version numbers are increased each time new data
579types (such as restricted hashes) are added to the vocabulary of the file
580format. This meant that a newer Storable module had no way of writing a
f062ea6c 581file readable by an older Storable, even if the writer didn't store newer
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582data types.
583
584This version of Storable will defer croaking until it encounters a data
585type in the file that it does not recognize. This means that it will
586continue to read files generated by newer Storable modules which are careful
587in what they write out, making it easier to upgrade Storable modules in a
588mixed environment.
589
590The old behaviour of immediate croaking can be re-instated by setting
f062ea6c 591C<$Storable::accept_future_minor> to some C<FALSE> value.
e8189732 592
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593=back
594
f062ea6c 595All these variables have no effect on a newer Perl which supports the
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596relevant feature.
597
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598=head1 ERROR REPORTING
599
600Storable uses the "exception" paradigm, in that it does not try to workaround
601failures: if something bad happens, an exception is generated from the
602caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
603those exceptions.
604
605When Storable croaks, it tries to report the error via the C<logcroak()>
606routine from the C<Log::Agent> package, if it is available.
607
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608Normal errors are reported by having store() or retrieve() return C<undef>.
609Such errors are usually I/O errors (or truncated stream errors at retrieval).
610
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611=head1 WIZARDS ONLY
612
613=head2 Hooks
614
615Any class may define hooks that will be called during the serialization
616and deserialization process on objects that are instances of that class.
617Those hooks can redefine the way serialization is performed (and therefore,
c261f00e 618how the symmetrical deserialization should be conducted).
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619
620Since we said earlier:
621
622 dclone(.) = thaw(freeze(.))
623
624everything we say about hooks should also hold for deep cloning. However,
625hooks get to know whether the operation is a mere serialization, or a cloning.
626
627Therefore, when serializing hooks are involved,
628
629 dclone(.) <> thaw(freeze(.))
630
631Well, you could keep them in sync, but there's no guarantee it will always
632hold on classes somebody else wrote. Besides, there is little to gain in
f062ea6c 633doing so: a serializing hook could keep only one attribute of an object,
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634which is probably not what should happen during a deep cloning of that
635same object.
636
637Here is the hooking interface:
638
bbc7dcd2 639=over 4
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640
641=item C<STORABLE_freeze> I<obj>, I<cloning>
642
643The serializing hook, called on the object during serialization. It can be
644inherited, or defined in the class itself, like any other method.
645
646Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
647whether we're in a dclone() or a regular serialization via store() or freeze().
648
649Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
650is the serialized form to be used, and the optional $ref1, $ref2, etc... are
651extra references that you wish to let the Storable engine serialize.
652
653At deserialization time, you will be given back the same LIST, but all the
654extra references will be pointing into the deserialized structure.
655
656The B<first time> the hook is hit in a serialization flow, you may have it
657return an empty list. That will signal the Storable engine to further
658discard that hook for this class and to therefore revert to the default
659serialization of the underlying Perl data. The hook will again be normally
660processed in the next serialization.
661
662Unless you know better, serializing hook should always say:
663
664 sub STORABLE_freeze {
665 my ($self, $cloning) = @_;
666 return if $cloning; # Regular default serialization
667 ....
668 }
669
670in order to keep reasonable dclone() semantics.
671
672=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
673
674The deserializing hook called on the object during deserialization.
f062ea6c 675But wait: if we're deserializing, there's no object yet... right?
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676
677Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
678you can view C<STORABLE_thaw> as an alternate creation routine.
679
680This means the hook can be inherited like any other method, and that
681I<obj> is your blessed reference for this particular instance.
682
683The other arguments should look familiar if you know C<STORABLE_freeze>:
684I<cloning> is true when we're part of a deep clone operation, I<serialized>
685is the serialized string you returned to the engine in C<STORABLE_freeze>,
686and there may be an optional list of references, in the same order you gave
687them at serialization time, pointing to the deserialized objects (which
688have been processed courtesy of the Storable engine).
689
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690When the Storable engine does not find any C<STORABLE_thaw> hook routine,
691it tries to load the class by requiring the package dynamically (using
692the blessed package name), and then re-attempts the lookup. If at that
693time the hook cannot be located, the engine croaks. Note that this mechanism
c261f00e 694will fail if you define several classes in the same file, but L<perlmod>
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695warned you.
696
f062ea6c 697It is up to you to use this information to populate I<obj> the way you want.
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698
699Returned value: none.
700
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701=item C<STORABLE_attach> I<class>, I<cloning>, I<serialized>
702
703While C<STORABLE_freeze> and C<STORABLE_thaw> are useful for classes where
3c4b39be 704each instance is independent, this mechanism has difficulty (or is
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705incompatible) with objects that exist as common process-level or
706system-level resources, such as singleton objects, database pools, caches
707or memoized objects.
708
709The alternative C<STORABLE_attach> method provides a solution for these
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710shared objects. Instead of C<STORABLE_freeze> --E<gt> C<STORABLE_thaw>,
711you implement C<STORABLE_freeze> --E<gt> C<STORABLE_attach> instead.
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712
713Arguments: I<class> is the class we are attaching to, I<cloning> is a flag
714indicating whether we're in a dclone() or a regular de-serialization via
715thaw(), and I<serialized> is the stored string for the resource object.
716
717Because these resource objects are considered to be owned by the entire
718process/system, and not the "property" of whatever is being serialized,
719no references underneath the object should be included in the serialized
720string. Thus, in any class that implements C<STORABLE_attach>, the
721C<STORABLE_freeze> method cannot return any references, and C<Storable>
722will throw an error if C<STORABLE_freeze> tries to return references.
723
724All information required to "attach" back to the shared resource object
725B<must> be contained B<only> in the C<STORABLE_freeze> return string.
726Otherwise, C<STORABLE_freeze> behaves as normal for C<STORABLE_attach>
727classes.
728
729Because C<STORABLE_attach> is passed the class (rather than an object),
730it also returns the object directly, rather than modifying the passed
731object.
732
733Returned value: object of type C<class>
734
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735=back
736
737=head2 Predicates
738
c261f00e 739Predicates are not exportable. They must be called by explicitly prefixing
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740them with the Storable package name.
741
bbc7dcd2 742=over 4
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743
744=item C<Storable::last_op_in_netorder>
745
746The C<Storable::last_op_in_netorder()> predicate will tell you whether
747network order was used in the last store or retrieve operation. If you
748don't know how to use this, just forget about it.
749
750=item C<Storable::is_storing>
751
752Returns true if within a store operation (via STORABLE_freeze hook).
753
754=item C<Storable::is_retrieving>
755
f062ea6c 756Returns true if within a retrieve operation (via STORABLE_thaw hook).
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757
758=back
759
760=head2 Recursion
761
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762With hooks comes the ability to recurse back to the Storable engine.
763Indeed, hooks are regular Perl code, and Storable is convenient when
764it comes to serializing and deserializing things, so why not use it
765to handle the serialization string?
7a6a85bf 766
f062ea6c 767There are a few things you need to know, however:
7a6a85bf 768
bbc7dcd2 769=over 4
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770
771=item *
772
773You can create endless loops if the things you serialize via freeze()
f062ea6c
PN
774(for instance) point back to the object we're trying to serialize in
775the hook.
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776
777=item *
778
779Shared references among objects will not stay shared: if we're serializing
780the list of object [A, C] where both object A and C refer to the SAME object
781B, and if there is a serializing hook in A that says freeze(B), then when
782deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
783a deep clone of B'. The topology was not preserved.
784
785=back
786
787That's why C<STORABLE_freeze> lets you provide a list of references
788to serialize. The engine guarantees that those will be serialized in the
789same context as the other objects, and therefore that shared objects will
790stay shared.
791
792In the above [A, C] example, the C<STORABLE_freeze> hook could return:
793
794 ("something", $self->{B})
795
796and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
797would get back the reference to the B' object, deserialized for you.
798
799Therefore, recursion should normally be avoided, but is nonetheless supported.
800
801=head2 Deep Cloning
802
f062ea6c 803There is a Clone module available on CPAN which implements deep cloning
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804natively, i.e. without freezing to memory and thawing the result. It is
805aimed to replace Storable's dclone() some day. However, it does not currently
806support Storable hooks to redefine the way deep cloning is performed.
807
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808=head1 Storable magic
809
810Yes, there's a lot of that :-) But more precisely, in UNIX systems
811there's a utility called C<file>, which recognizes data files based on
812their contents (usually their first few bytes). For this to work,
8b793558 813a certain file called F<magic> needs to taught about the I<signature>
0a0da639 814of the data. Where that configuration file lives depends on the UNIX
f062ea6c 815flavour; often it's something like F</usr/share/misc/magic> or
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816F</etc/magic>. Your system administrator needs to do the updating of
817the F<magic> file. The necessary signature information is output to
f062ea6c
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818STDOUT by invoking Storable::show_file_magic(). Note that the GNU
819implementation of the C<file> utility, version 3.38 or later,
820is expected to contain support for recognising Storable files
821out-of-the-box, in addition to other kinds of Perl files.
0a0da639 822
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823=head1 EXAMPLES
824
825Here are some code samples showing a possible usage of Storable:
826
827 use Storable qw(store retrieve freeze thaw dclone);
828
829 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
830
2359510d 831 store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n";
7a6a85bf 832
2359510d
SD
833 $colref = retrieve('mycolors');
834 die "Unable to retrieve from mycolors!\n" unless defined $colref;
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835 printf "Blue is still %lf\n", $colref->{'Blue'};
836
837 $colref2 = dclone(\%color);
838
839 $str = freeze(\%color);
840 printf "Serialization of %%color is %d bytes long.\n", length($str);
841 $colref3 = thaw($str);
842
843which prints (on my machine):
844
845 Blue is still 0.100000
846 Serialization of %color is 102 bytes long.
847
d2b96869
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848Serialization of CODE references and deserialization in a safe
849compartment:
850
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851=for example begin
852
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853 use Storable qw(freeze thaw);
854 use Safe;
855 use strict;
856 my $safe = new Safe;
197b90bc 857 # because of opcodes used in "use strict":
d1e2299c 858 $safe->permit(qw(:default require));
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859 local $Storable::Deparse = 1;
860 local $Storable::Eval = sub { $safe->reval($_[0]) };
197b90bc 861 my $serialized = freeze(sub { 42 });
d2b96869 862 my $code = thaw($serialized);
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863 $code->() == 42;
864
865=for example end
866
867=for example_testing
868 is( $code->(), 42 );
d2b96869 869
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870=head1 WARNING
871
872If you're using references as keys within your hash tables, you're bound
f062ea6c 873to be disappointed when retrieving your data. Indeed, Perl stringifies
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874references used as hash table keys. If you later wish to access the
875items via another reference stringification (i.e. using the same
876reference that was used for the key originally to record the value into
877the hash table), it will work because both references stringify to the
878same string.
879
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880It won't work across a sequence of C<store> and C<retrieve> operations,
881however, because the addresses in the retrieved objects, which are
882part of the stringified references, will probably differ from the
883original addresses. The topology of your structure is preserved,
884but not hidden semantics like those.
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885
886On platforms where it matters, be sure to call C<binmode()> on the
887descriptors that you pass to Storable functions.
888
889Storing data canonically that contains large hashes can be
890significantly slower than storing the same data normally, as
c261f00e 891temporary arrays to hold the keys for each hash have to be allocated,
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892populated, sorted and freed. Some tests have shown a halving of the
893speed of storing -- the exact penalty will depend on the complexity of
894your data. There is no slowdown on retrieval.
895
896=head1 BUGS
897
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898You can't store GLOB, FORMLINE, etc.... If you can define semantics
899for those operations, feel free to enhance Storable so that it can
900deal with them.
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901
902The store functions will C<croak> if they run into such references
903unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
904case, the fatal message is turned in a warning and some
905meaningless string is stored instead.
906
907Setting C<$Storable::canonical> may not yield frozen strings that
908compare equal due to possible stringification of numbers. When the
f062ea6c 909string version of a scalar exists, it is the form stored; therefore,
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910if you happen to use your numbers as strings between two freezing
911operations on the same data structures, you will get different
912results.
913
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914When storing doubles in network order, their value is stored as text.
915However, you should also not expect non-numeric floating-point values
916such as infinity and "not a number" to pass successfully through a
917nstore()/retrieve() pair.
918
919As Storable neither knows nor cares about character sets (although it
920does know that characters may be more than eight bits wide), any difference
921in the interpretation of character codes between a host and a target
922system is your problem. In particular, if host and target use different
923code points to represent the characters used in the text representation
924of floating-point numbers, you will not be able be able to exchange
925floating-point data, even with nstore().
926
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927C<Storable::drop_utf8> is a blunt tool. There is no facility either to
928return B<all> strings as utf8 sequences, or to attempt to convert utf8
929data back to 8 bit and C<croak()> if the conversion fails.
930
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931Prior to Storable 2.01, no distinction was made between signed and
932unsigned integers on storing. By default Storable prefers to store a
933scalars string representation (if it has one) so this would only cause
3c4b39be 934problems when storing large unsigned integers that had never been converted
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935to string or floating point. In other words values that had been generated
936by integer operations such as logic ops and then not used in any string or
937arithmetic context before storing.
938
939=head2 64 bit data in perl 5.6.0 and 5.6.1
940
941This section only applies to you if you have existing data written out
942by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which
943has been configured with 64 bit integer support (not the default)
944If you got a precompiled perl, rather than running Configure to build
945your own perl from source, then it almost certainly does not affect you,
946and you can stop reading now (unless you're curious). If you're using perl
947on Windows it does not affect you.
948
949Storable writes a file header which contains the sizes of various C
950language types for the C compiler that built Storable (when not writing in
951network order), and will refuse to load files written by a Storable not
952on the same (or compatible) architecture. This check and a check on
953machine byteorder is needed because the size of various fields in the file
954are given by the sizes of the C language types, and so files written on
955different architectures are incompatible. This is done for increased speed.
956(When writing in network order, all fields are written out as standard
957lengths, which allows full interworking, but takes longer to read and write)
958
959Perl 5.6.x introduced the ability to optional configure the perl interpreter
960to use C's C<long long> type to allow scalars to store 64 bit integers on 32
961bit systems. However, due to the way the Perl configuration system
962generated the C configuration files on non-Windows platforms, and the way
963Storable generates its header, nothing in the Storable file header reflected
964whether the perl writing was using 32 or 64 bit integers, despite the fact
965that Storable was storing some data differently in the file. Hence Storable
966running on perl with 64 bit integers will read the header from a file
967written by a 32 bit perl, not realise that the data is actually in a subtly
968incompatible format, and then go horribly wrong (possibly crashing) if it
969encountered a stored integer. This is a design failure.
970
971Storable has now been changed to write out and read in a file header with
972information about the size of integers. It's impossible to detect whether
973an old file being read in was written with 32 or 64 bit integers (they have
974the same header) so it's impossible to automatically switch to a correct
975backwards compatibility mode. Hence this Storable defaults to the new,
976correct behaviour.
977
978What this means is that if you have data written by Storable 1.x running
979on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux
980then by default this Storable will refuse to read it, giving the error
981I<Byte order is not compatible>. If you have such data then you you
982should set C<$Storable::interwork_56_64bit> to a true value to make this
983Storable read and write files with the old header. You should also
984migrate your data, or any older perl you are communicating with, to this
985current version of Storable.
986
987If you don't have data written with specific configuration of perl described
988above, then you do not and should not do anything. Don't set the flag -
989not only will Storable on an identically configured perl refuse to load them,
990but Storable a differently configured perl will load them believing them
991to be correct for it, and then may well fail or crash part way through
992reading them.
993
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994=head1 CREDITS
995
996Thank you to (in chronological order):
997
998 Jarkko Hietaniemi <jhi@iki.fi>
999 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
1000 Benjamin A. Holzman <bah@ecnvantage.com>
1001 Andrew Ford <A.Ford@ford-mason.co.uk>
1002 Gisle Aas <gisle@aas.no>
1003 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
1004 Murray Nesbitt <murray@activestate.com>
1005 Marc Lehmann <pcg@opengroup.org>
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1006 Justin Banks <justinb@wamnet.com>
1007 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
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1008 Salvador Ortiz Garcia <sog@msg.com.mx>
1009 Dominic Dunlop <domo@computer.org>
1010 Erik Haugan <erik@solbors.no>
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1011
1012for their bug reports, suggestions and contributions.
1013
1014Benjamin Holzman contributed the tied variable support, Andrew Ford
1015contributed the canonical order for hashes, and Gisle Aas fixed
f062ea6c 1016a few misunderstandings of mine regarding the perl internals,
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1017and optimized the emission of "tags" in the output streams by
1018simply counting the objects instead of tagging them (leading to
1019a binary incompatibility for the Storable image starting at version
f062ea6c 10200.6--older images are, of course, still properly understood).
7a6a85bf 1021Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
f062ea6c 1022and references to tied items support.
7a6a85bf 1023
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1024=head1 AUTHOR
1025
0ba8809e 1026Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
775ecd75 1027Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>>
0ba8809e
NC
1028
1029Please e-mail us with problems, bug fixes, comments and complaints,
1030although if you have complements you should send them to Raphael.
1031Please don't e-mail Raphael with problems, as he no longer works on
1032Storable, and your message will be delayed while he forwards it to us.
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1033
1034=head1 SEE ALSO
1035
c261f00e 1036L<Clone>.
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1037
1038=cut