1 ;# $Id: Storable.pm,v 1.0.1.13 2001/12/01 13:34:49 ram Exp $
3 ;# Copyright (c) 1995-2000, Raphael Manfredi
5 ;# You may redistribute only under the same terms as Perl 5, as specified
6 ;# in the README file that comes with the distribution.
8 ;# $Log: Storable.pm,v $
9 ;# Revision 1.0.1.13 2001/12/01 13:34:49 ram
10 ;# patch14: avoid requiring Fcntl upfront, useful to embedded runtimes
11 ;# patch14: store_fd() will now correctly autoflush file if needed
13 ;# Revision 1.0.1.12 2001/08/28 21:51:51 ram
14 ;# patch13: fixed truncation race with lock_retrieve() in lock_store()
16 ;# Revision 1.0.1.11 2001/07/01 11:22:14 ram
17 ;# patch12: systematically use "=over 4" for POD linters
18 ;# patch12: updated version number
20 ;# Revision 1.0.1.10 2001/03/15 00:20:25 ram
21 ;# patch11: updated version number
23 ;# Revision 1.0.1.9 2001/02/17 12:37:32 ram
24 ;# patch10: forgot to increase version number at previous patch
26 ;# Revision 1.0.1.8 2001/02/17 12:24:37 ram
27 ;# patch8: fixed incorrect error message
29 ;# Revision 1.0.1.7 2001/01/03 09:39:02 ram
30 ;# patch7: added CAN_FLOCK to determine whether we can flock() or not
32 ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram
33 ;# patch6: increased version number
35 ;# Revision 1.0.1.5 2000/10/26 17:10:18 ram
36 ;# patch5: documented that store() and retrieve() can return undef
37 ;# patch5: added paragraph explaining the auto require for thaw hooks
39 ;# Revision 1.0.1.4 2000/10/23 18:02:57 ram
40 ;# patch4: protected calls to flock() for dos platform
41 ;# patch4: added logcarp emulation if they don't have Log::Agent
43 ;# Revision 1.0.1.3 2000/09/29 19:49:01 ram
44 ;# patch3: updated version number
46 ;# Revision 1.0.1.2 2000/09/28 21:42:51 ram
47 ;# patch2: added lock_store lock_nstore lock_retrieve
49 ;# Revision 1.0.1.1 2000/09/17 16:46:21 ram
50 ;# patch1: documented that doubles are stringified by nstore()
51 ;# patch1: added Salvador Ortiz Garcia in CREDITS section
53 ;# Revision 1.0 2000/09/01 19:40:41 ram
54 ;# Baseline for first official release.
59 package Storable; @ISA = qw(Exporter DynaLoader);
61 @EXPORT = qw(store retrieve);
63 nstore store_fd nstore_fd fd_retrieve
67 lock_store lock_nstore lock_retrieve
71 use vars qw($forgive_me $VERSION);
74 *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr...
77 # Use of Log::Agent is optional
80 eval "use Log::Agent";
85 # They might miss :flock in Fcntl
89 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {
90 Fcntl->import(':flock');
99 # Can't Autoload cleanly as this clashes 8.3 with &retrieve
100 sub retrieve_fd { &fd_retrieve } # Backward compatibility
102 # By default restricted hashes are downgraded on earlier perls.
104 $Storable::downgrade_restricted = 1;
105 $Storable::accept_future_minor = 1;
110 # Use of Log::Agent is optional. If it hasn't imported these subs then
111 # Autoloader will kindly supply our fallback implementation.
123 # Determine whether locking is possible, but only when needed.
126 sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
127 return $CAN_FLOCK if defined $CAN_FLOCK;
128 require Config; import Config;
130 $Config{'d_flock'} ||
131 $Config{'d_fcntl_can_lock'} ||
135 sub show_file_magic {
138 # To recognize the data files of the Perl module Storable,
139 # the following lines need to be added to the local magic(5) file,
140 # usually either /usr/share/misc/magic or /etc/magic.
142 0 string perl-store perl Storable(v0.6) data
143 >4 byte >0 (net-order %d)
144 >>4 byte &01 (network-ordered)
145 >>4 byte =3 (major 1)
146 >>4 byte =2 (major 1)
148 0 string pst0 perl Storable(v0.7) data
150 >>4 byte &01 (network-ordered)
151 >>4 byte =5 (major 2)
152 >>4 byte =4 (major 2)
153 >>5 byte >0 (minor %d)
159 return unless defined $header and length $header > 11;
161 if ($header =~ s/^perl-store//) {
162 die "Can't deal with version 0 headers";
163 } elsif ($header =~ s/^pst0//) {
166 # Assume it's a string.
167 my ($major, $minor, $bytelen) = unpack "C3", $header;
169 my $net_order = $major & 1;
171 @$result{qw(major minor netorder)} = ($major, $minor, $net_order);
173 return $result if $net_order;
175 # I assume that it is rare to find v1 files, so this is an intentionally
176 # inefficient way of doing it, to make the rest of the code constant.
178 delete $result->{minor};
179 $header = '.' . $header;
183 @$result{qw(byteorder intsize longsize ptrsize)} =
184 unpack "x3 A$bytelen C3", $header;
186 if ($major >= 2 and $minor >= 2) {
187 $result->{nvsize} = unpack "x6 x$bytelen C", $header;
195 # Store target object hierarchy, identified by a reference to its root.
196 # The stored object tree may later be retrieved to memory via retrieve.
197 # Returns undef if an I/O error occurred, in which case the file is
201 return _store(\&pstore, @_, 0);
207 # Same as store, but in network order.
210 return _store(\&net_pstore, @_, 0);
216 # Same as store, but flock the file first (advisory locking).
219 return _store(\&pstore, @_, 1);
225 # Same as nstore, but flock the file first (advisory locking).
228 return _store(\&net_pstore, @_, 1);
231 # Internal store to file routine
235 my ($file, $use_locking) = @_;
236 logcroak "not a reference" unless ref($self);
237 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
240 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
241 unless (&CAN_FLOCK) {
242 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
245 flock(FILE, LOCK_EX) ||
246 logcroak "can't get exclusive lock on $file: $!";
248 # Unlocking will happen when FILE is closed
250 open(FILE, ">$file") || logcroak "can't create $file: $!";
252 binmode FILE; # Archaic systems...
253 my $da = $@; # Don't mess if called from exception handler
255 # Call C routine nstore or pstore, depending on network order
256 eval { $ret = &$xsptr(*FILE, $self) };
257 close(FILE) or $ret = undef;
258 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
259 logcroak $@ if $@ =~ s/\.?\n$/,/;
261 return $ret ? $ret : undef;
267 # Same as store, but perform on an already opened file descriptor instead.
268 # Returns undef if an I/O error occurred.
271 return _store_fd(\&pstore, @_);
277 # Same as store_fd, but in network order.
280 my ($self, $file) = @_;
281 return _store_fd(\&net_pstore, @_);
284 # Internal store routine on opened file descriptor
289 logcroak "not a reference" unless ref($self);
290 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
291 my $fd = fileno($file);
292 logcroak "not a valid file descriptor" unless defined $fd;
293 my $da = $@; # Don't mess if called from exception handler
295 # Call C routine nstore or pstore, depending on network order
296 eval { $ret = &$xsptr($file, $self) };
297 logcroak $@ if $@ =~ s/\.?\n$/,/;
298 local $\; print $file ''; # Autoflush the file if wanted
300 return $ret ? $ret : undef;
306 # Store oject and its hierarchy in memory and return a scalar
307 # containing the result.
310 _freeze(\&mstore, @_);
316 # Same as freeze but in network order.
319 _freeze(\&net_mstore, @_);
322 # Internal freeze routine
326 logcroak "not a reference" unless ref($self);
327 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
328 my $da = $@; # Don't mess if called from exception handler
330 # Call C routine mstore or net_mstore, depending on network order
331 eval { $ret = &$xsptr($self) };
332 logcroak $@ if $@ =~ s/\.?\n$/,/;
334 return $ret ? $ret : undef;
340 # Retrieve object hierarchy from disk, returning a reference to the root
341 # object of that tree.
350 # Same as retrieve, but with advisory locking.
356 # Internal retrieve routine
358 my ($file, $use_locking) = @_;
360 open(FILE, $file) || logcroak "can't open $file: $!";
361 binmode FILE; # Archaic systems...
363 my $da = $@; # Could be from exception handler
365 unless (&CAN_FLOCK) {
366 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
369 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
370 # Unlocking will happen when FILE is closed
372 eval { $self = pretrieve(*FILE) }; # Call C routine
374 logcroak $@ if $@ =~ s/\.?\n$/,/;
382 # Same as retrieve, but perform from an already opened file descriptor instead.
386 my $fd = fileno($file);
387 logcroak "not a valid file descriptor" unless defined $fd;
389 my $da = $@; # Could be from exception handler
390 eval { $self = pretrieve($file) }; # Call C routine
391 logcroak $@ if $@ =~ s/\.?\n$/,/;
399 # Recreate objects in memory from an existing frozen image created
400 # by freeze. If the frozen image passed is undef, return undef.
404 return undef unless defined $frozen;
406 my $da = $@; # Could be from exception handler
407 eval { $self = mretrieve($frozen) }; # Call C routine
408 logcroak $@ if $@ =~ s/\.?\n$/,/;
415 Storable - persistency for perl data structures
420 store \%table, 'file';
421 $hashref = retrieve('file');
423 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
426 nstore \%table, 'file';
427 $hashref = retrieve('file'); # There is NO nretrieve()
429 # Storing to and retrieving from an already opened file
430 store_fd \@array, \*STDOUT;
431 nstore_fd \%table, \*STDOUT;
432 $aryref = fd_retrieve(\*SOCKET);
433 $hashref = fd_retrieve(\*SOCKET);
435 # Serializing to memory
436 $serialized = freeze \%table;
437 %table_clone = %{ thaw($serialized) };
439 # Deep (recursive) cloning
440 $cloneref = dclone($ref);
443 use Storable qw(lock_store lock_nstore lock_retrieve)
444 lock_store \%table, 'file';
445 lock_nstore \%table, 'file';
446 $hashref = lock_retrieve('file');
450 The Storable package brings persistence to your perl data structures
451 containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
452 conveniently stored to disk and retrieved at a later time.
454 It can be used in the regular procedural way by calling C<store> with
455 a reference to the object to be stored, along with the file name where
456 the image should be written.
458 The routine returns C<undef> for I/O problems or other internal error,
459 a true value otherwise. Serious errors are propagated as a C<die> exception.
461 To retrieve data stored to disk, use C<retrieve> with a file name,
462 and the objects stored into that file are recreated into memory for you,
463 a I<reference> to the root object being returned. In case an I/O error
464 occurs while reading, C<undef> is returned instead. Other serious
465 errors are propagated via C<die>.
467 Since storage is performed recursively, you might want to stuff references
468 to objects that share a lot of common data into a single array or hash
469 table, and then store that object. That way, when you retrieve back the
470 whole thing, the objects will continue to share what they originally shared.
472 At the cost of a slight header overhead, you may store to an already
473 opened file descriptor using the C<store_fd> routine, and retrieve
474 from a file via C<fd_retrieve>. Those names aren't imported by default,
475 so you will have to do that explicitly if you need those routines.
476 The file descriptor you supply must be already opened, for read
477 if you're going to retrieve and for write if you wish to store.
479 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
480 $hashref = fd_retrieve(*STDIN);
482 You can also store data in network order to allow easy sharing across
483 multiple platforms, or when storing on a socket known to be remotely
484 connected. The routines to call have an initial C<n> prefix for I<network>,
485 as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
486 correctly restored so you don't have to know whether you're restoring
487 from native or network ordered data. Double values are stored stringified
488 to ensure portability as well, at the slight risk of loosing some precision
489 in the last decimals.
491 When using C<fd_retrieve>, objects are retrieved in sequence, one
492 object (i.e. one recursive tree) per associated C<store_fd>.
494 If you're more from the object-oriented camp, you can inherit from
495 Storable and directly store your objects by invoking C<store> as
496 a method. The fact that the root of the to-be-stored tree is a
497 blessed reference (i.e. an object) is special-cased so that the
498 retrieve does not provide a reference to that object but rather the
499 blessed object reference itself. (Otherwise, you'd get a reference
500 to that blessed object).
504 The Storable engine can also store data into a Perl scalar instead, to
505 later retrieve them. This is mainly used to freeze a complex structure in
506 some safe compact memory place (where it can possibly be sent to another
507 process via some IPC, since freezing the structure also serializes it in
508 effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
509 out and recreate the original complex structure in memory.
511 Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
512 If you wish to send out the frozen scalar to another machine, use
513 C<nfreeze> instead to get a portable image.
515 Note that freezing an object structure and immediately thawing it
516 actually achieves a deep cloning of that structure:
518 dclone(.) = thaw(freeze(.))
520 Storable provides you with a C<dclone> interface which does not create
521 that intermediary scalar but instead freezes the structure in some
522 internal memory space and then immediately thaws it out.
524 =head1 ADVISORY LOCKING
526 The C<lock_store> and C<lock_nstore> routine are equivalent to C<store>
527 and C<nstore>, only they get an exclusive lock on the file before
528 writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also
529 gets a shared lock on the file before reading.
531 Like with any advisory locking scheme, the protection only works if
532 you systematically use C<lock_store> and C<lock_retrieve>. If one
533 side of your application uses C<store> whilst the other uses C<lock_retrieve>,
534 you will get no protection at all.
536 The internal advisory locking is implemented using Perl's flock() routine.
537 If your system does not support any form of flock(), or if you share
538 your files across NFS, you might wish to use other forms of locking by
539 using modules like LockFile::Simple which lock a file using a filesystem
540 entry, instead of locking the file descriptor.
544 The heart of Storable is written in C for decent speed. Extra low-level
545 optimizations have been made when manipulating perl internals, to
546 sacrifice encapsulation for the benefit of greater speed.
548 =head1 CANONICAL REPRESENTATION
550 Normally Storable stores elements of hashes in the order they are
551 stored internally by Perl, i.e. pseudo-randomly. If you set
552 C<$Storable::canonical> to some C<TRUE> value, Storable will store
553 hashes with the elements sorted by their key. This allows you to
554 compare data structures by comparing their frozen representations (or
555 even the compressed frozen representations), which can be useful for
556 creating lookup tables for complicated queries.
558 Canonical order does not imply network order, those are two orthogonal
561 =head1 FORWARD COMPATIBILITY
563 This release of Storable can be used on a newer version of Perl to
564 serialize data which is not supported by earlier Perls. By default
565 Storable will attempt to do the right thing, by C<croak()>ing if it
566 encounters data that it cannot deserialize. However, the defaults
567 can be changed as follows
573 Perl 5.6 added support for Unicode characters with code points > 255,
574 and Perl 5.8 has full support for Unicode characters in hash keys.
575 Perl internally encodes strings with these characters using utf8, and
576 Storable serializes them as utf8. By default, if an older version of
577 Perl encounters a utf8 value it cannot represent, it will C<croak()>.
578 To change this behaviour so that Storable deserializes utf8 encoded
579 values as the string of bytes (effectively dropping the I<is_utf8> flag)
580 set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
581 data loss, because with C<$drop_utf8> true, it becomes impossible to tell
582 whether the original data was the Unicode string, or a series of bytes
583 that happen to be valid utf8.
585 =item restricted hashes
587 Perl 5.8 adds support for restricted hashes, which have keys restricted to
588 a given set, and can have values locked to be read only. By default
589 when Storable encounters a restricted hash on a perl that doesn't support
590 them, it will deserialize it as a normal hash, silently discarding any
591 placeholder keys and leaving the keys and all values unlocked. To make
592 Storable C<croak()> instead, set C<$Storable::downgrade_restricted> to
593 a false value. To restore the default set it back to some C<TRUE> value.
595 =item files from future versions of Storable
597 Earlier versions of Storable would immediately croak if they encountered
598 a file with a higher internal version number than the reading Storable
599 knew about. Internal version numbers are increased each time new data
600 types (such as restricted hashes) are added to the vocabulary of the file
601 format. This meant that a newer Storable module had no way of writing a
602 file readable by an older Storable, even if writer didn't store newer
605 This version of Storable will defer croaking until it encounters a data
606 type in the file that it does not recognize. This means that it will
607 continue to read files generated by newer Storable modules which are careful
608 in what they write out, making it easier to upgrade Storable modules in a
611 The old behaviour of immediate croaking can be re-instated by setting
612 C<$Storable::accept_future_minor> to false.
616 Both these variables have no effect on a newer Perl which supports the
619 =head1 ERROR REPORTING
621 Storable uses the "exception" paradigm, in that it does not try to workaround
622 failures: if something bad happens, an exception is generated from the
623 caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
626 When Storable croaks, it tries to report the error via the C<logcroak()>
627 routine from the C<Log::Agent> package, if it is available.
629 Normal errors are reported by having store() or retrieve() return C<undef>.
630 Such errors are usually I/O errors (or truncated stream errors at retrieval).
636 Any class may define hooks that will be called during the serialization
637 and deserialization process on objects that are instances of that class.
638 Those hooks can redefine the way serialization is performed (and therefore,
639 how the symmetrical deserialization should be conducted).
641 Since we said earlier:
643 dclone(.) = thaw(freeze(.))
645 everything we say about hooks should also hold for deep cloning. However,
646 hooks get to know whether the operation is a mere serialization, or a cloning.
648 Therefore, when serializing hooks are involved,
650 dclone(.) <> thaw(freeze(.))
652 Well, you could keep them in sync, but there's no guarantee it will always
653 hold on classes somebody else wrote. Besides, there is little to gain in
654 doing so: a serializing hook could only keep one attribute of an object,
655 which is probably not what should happen during a deep cloning of that
658 Here is the hooking interface:
662 =item C<STORABLE_freeze> I<obj>, I<cloning>
664 The serializing hook, called on the object during serialization. It can be
665 inherited, or defined in the class itself, like any other method.
667 Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
668 whether we're in a dclone() or a regular serialization via store() or freeze().
670 Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
671 is the serialized form to be used, and the optional $ref1, $ref2, etc... are
672 extra references that you wish to let the Storable engine serialize.
674 At deserialization time, you will be given back the same LIST, but all the
675 extra references will be pointing into the deserialized structure.
677 The B<first time> the hook is hit in a serialization flow, you may have it
678 return an empty list. That will signal the Storable engine to further
679 discard that hook for this class and to therefore revert to the default
680 serialization of the underlying Perl data. The hook will again be normally
681 processed in the next serialization.
683 Unless you know better, serializing hook should always say:
685 sub STORABLE_freeze {
686 my ($self, $cloning) = @_;
687 return if $cloning; # Regular default serialization
691 in order to keep reasonable dclone() semantics.
693 =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
695 The deserializing hook called on the object during deserialization.
696 But wait. If we're deserializing, there's no object yet... right?
698 Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
699 you can view C<STORABLE_thaw> as an alternate creation routine.
701 This means the hook can be inherited like any other method, and that
702 I<obj> is your blessed reference for this particular instance.
704 The other arguments should look familiar if you know C<STORABLE_freeze>:
705 I<cloning> is true when we're part of a deep clone operation, I<serialized>
706 is the serialized string you returned to the engine in C<STORABLE_freeze>,
707 and there may be an optional list of references, in the same order you gave
708 them at serialization time, pointing to the deserialized objects (which
709 have been processed courtesy of the Storable engine).
711 When the Storable engine does not find any C<STORABLE_thaw> hook routine,
712 it tries to load the class by requiring the package dynamically (using
713 the blessed package name), and then re-attempts the lookup. If at that
714 time the hook cannot be located, the engine croaks. Note that this mechanism
715 will fail if you define several classes in the same file, but L<perlmod>
718 It is up to you to use these information to populate I<obj> the way you want.
720 Returned value: none.
726 Predicates are not exportable. They must be called by explicitly prefixing
727 them with the Storable package name.
731 =item C<Storable::last_op_in_netorder>
733 The C<Storable::last_op_in_netorder()> predicate will tell you whether
734 network order was used in the last store or retrieve operation. If you
735 don't know how to use this, just forget about it.
737 =item C<Storable::is_storing>
739 Returns true if within a store operation (via STORABLE_freeze hook).
741 =item C<Storable::is_retrieving>
743 Returns true if within a retrieve operation, (via STORABLE_thaw hook).
749 With hooks comes the ability to recurse back to the Storable engine. Indeed,
750 hooks are regular Perl code, and Storable is convenient when it comes to
751 serialize and deserialize things, so why not use it to handle the
752 serialization string?
754 There are a few things you need to know however:
760 You can create endless loops if the things you serialize via freeze()
761 (for instance) point back to the object we're trying to serialize in the hook.
765 Shared references among objects will not stay shared: if we're serializing
766 the list of object [A, C] where both object A and C refer to the SAME object
767 B, and if there is a serializing hook in A that says freeze(B), then when
768 deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
769 a deep clone of B'. The topology was not preserved.
773 That's why C<STORABLE_freeze> lets you provide a list of references
774 to serialize. The engine guarantees that those will be serialized in the
775 same context as the other objects, and therefore that shared objects will
778 In the above [A, C] example, the C<STORABLE_freeze> hook could return:
780 ("something", $self->{B})
782 and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
783 would get back the reference to the B' object, deserialized for you.
785 Therefore, recursion should normally be avoided, but is nonetheless supported.
789 There is a new Clone module available on CPAN which implements deep cloning
790 natively, i.e. without freezing to memory and thawing the result. It is
791 aimed to replace Storable's dclone() some day. However, it does not currently
792 support Storable hooks to redefine the way deep cloning is performed.
794 =head1 Storable magic
796 Yes, there's a lot of that :-) But more precisely, in UNIX systems
797 there's a utility called C<file>, which recognizes data files based on
798 their contents (usually their first few bytes). For this to work,
799 a certain file called F<magic> needs to taught about the I<signature>
800 of the data. Where that configuration file lives depends on the UNIX
801 flavour, often it's something like F</usr/share/misc/magic> or
802 F</etc/magic>. Your system administrator needs to do the updating of
803 the F<magic> file. The necessary signature information is output to
804 STDOUT by invoking Storable::show_file_magic(). Note that the open
805 source implementation of the C<file> utility 3.38 (or later)
806 is expected to contain the support for recognising Storable files,
807 in addition to other kinds of Perl files.
811 Here are some code samples showing a possible usage of Storable:
813 use Storable qw(store retrieve freeze thaw dclone);
815 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
817 store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";
819 $colref = retrieve('/tmp/colors');
820 die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
821 printf "Blue is still %lf\n", $colref->{'Blue'};
823 $colref2 = dclone(\%color);
825 $str = freeze(\%color);
826 printf "Serialization of %%color is %d bytes long.\n", length($str);
827 $colref3 = thaw($str);
829 which prints (on my machine):
831 Blue is still 0.100000
832 Serialization of %color is 102 bytes long.
836 If you're using references as keys within your hash tables, you're bound
837 to disappointment when retrieving your data. Indeed, Perl stringifies
838 references used as hash table keys. If you later wish to access the
839 items via another reference stringification (i.e. using the same
840 reference that was used for the key originally to record the value into
841 the hash table), it will work because both references stringify to the
844 It won't work across a C<store> and C<retrieve> operations however, because
845 the addresses in the retrieved objects, which are part of the stringified
846 references, will probably differ from the original addresses. The
847 topology of your structure is preserved, but not hidden semantics
850 On platforms where it matters, be sure to call C<binmode()> on the
851 descriptors that you pass to Storable functions.
853 Storing data canonically that contains large hashes can be
854 significantly slower than storing the same data normally, as
855 temporary arrays to hold the keys for each hash have to be allocated,
856 populated, sorted and freed. Some tests have shown a halving of the
857 speed of storing -- the exact penalty will depend on the complexity of
858 your data. There is no slowdown on retrieval.
862 You can't store GLOB, CODE, FORMLINE, etc... If you can define
863 semantics for those operations, feel free to enhance Storable so that
864 it can deal with them.
866 The store functions will C<croak> if they run into such references
867 unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
868 case, the fatal message is turned in a warning and some
869 meaningless string is stored instead.
871 Setting C<$Storable::canonical> may not yield frozen strings that
872 compare equal due to possible stringification of numbers. When the
873 string version of a scalar exists, it is the form stored, therefore
874 if you happen to use your numbers as strings between two freezing
875 operations on the same data structures, you will get different
878 When storing doubles in network order, their value is stored as text.
879 However, you should also not expect non-numeric floating-point values
880 such as infinity and "not a number" to pass successfully through a
881 nstore()/retrieve() pair.
883 As Storable neither knows nor cares about character sets (although it
884 does know that characters may be more than eight bits wide), any difference
885 in the interpretation of character codes between a host and a target
886 system is your problem. In particular, if host and target use different
887 code points to represent the characters used in the text representation
888 of floating-point numbers, you will not be able be able to exchange
889 floating-point data, even with nstore().
891 C<Storable::drop_utf8> is a blunt tool. There is no facility either to
892 return B<all> strings as utf8 sequences, or to attempt to convert utf8
893 data back to 8 bit and C<croak()> if the conversion fails.
897 Thank you to (in chronological order):
899 Jarkko Hietaniemi <jhi@iki.fi>
900 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
901 Benjamin A. Holzman <bah@ecnvantage.com>
902 Andrew Ford <A.Ford@ford-mason.co.uk>
903 Gisle Aas <gisle@aas.no>
904 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
905 Murray Nesbitt <murray@activestate.com>
906 Marc Lehmann <pcg@opengroup.org>
907 Justin Banks <justinb@wamnet.com>
908 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
909 Salvador Ortiz Garcia <sog@msg.com.mx>
910 Dominic Dunlop <domo@computer.org>
911 Erik Haugan <erik@solbors.no>
913 for their bug reports, suggestions and contributions.
915 Benjamin Holzman contributed the tied variable support, Andrew Ford
916 contributed the canonical order for hashes, and Gisle Aas fixed
917 a few misunderstandings of mine regarding the Perl internals,
918 and optimized the emission of "tags" in the output streams by
919 simply counting the objects instead of tagging them (leading to
920 a binary incompatibility for the Storable image starting at version
921 0.6--older images are of course still properly understood).
922 Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
923 and reference to tied items support.
927 Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
928 Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>>
930 Please e-mail us with problems, bug fixes, comments and complaints,
931 although if you have complements you should send them to Raphael.
932 Please don't e-mail Raphael with problems, as he no longer works on
933 Storable, and your message will be delayed while he forwards it to us.