3 perltie - how to hide an object class in a simple variable
7 tie VARIABLE, CLASSNAME, LIST
9 $object = tied VARIABLE
15 Prior to release 5.0 of Perl, a programmer could use dbmopen()
16 to connect an on-disk database in the standard Unix dbm(3x)
17 format magically to a %HASH in their program. However, their Perl was either
18 built with one particular dbm library or another, but not both, and
19 you couldn't extend this mechanism to other packages or types of variables.
23 The tie() function binds a variable to a class (package) that will provide
24 the implementation for access methods for that variable. Once this magic
25 has been performed, accessing a tied variable automatically triggers
26 method calls in the proper class. The complexity of the class is
27 hidden behind magic methods calls. The method names are in ALL CAPS,
28 which is a convention that Perl uses to indicate that they're called
29 implicitly rather than explicitly--just like the BEGIN() and END()
32 In the tie() call, C<VARIABLE> is the name of the variable to be
33 enchanted. C<CLASSNAME> is the name of a class implementing objects of
34 the correct type. Any additional arguments in the C<LIST> are passed to
35 the appropriate constructor method for that class--meaning TIESCALAR(),
36 TIEARRAY(), TIEHASH(), or TIEHANDLE(). (Typically these are arguments
37 such as might be passed to the dbminit() function of C.) The object
38 returned by the "new" method is also returned by the tie() function,
39 which would be useful if you wanted to access other methods in
40 C<CLASSNAME>. (You don't actually have to return a reference to a right
41 "type" (e.g., HASH or C<CLASSNAME>) so long as it's a properly blessed
42 object.) You can also retrieve a reference to the underlying object
43 using the tied() function.
45 Unlike dbmopen(), the tie() function will not C<use> or C<require> a module
46 for you--you need to do that explicitly yourself.
50 A class implementing a tied scalar should define the following methods:
51 TIESCALAR, FETCH, STORE, and possibly UNTIE and/or DESTROY.
53 Let's look at each in turn, using as an example a tie class for
54 scalars that allows the user to do something like:
56 tie $his_speed, 'Nice', getppid();
57 tie $my_speed, 'Nice', $$;
59 And now whenever either of those variables is accessed, its current
60 system priority is retrieved and returned. If those variables are set,
61 then the process's priority is changed!
63 We'll use Jarkko Hietaniemi <F<jhi@iki.fi>>'s BSD::Resource class (not
64 included) to access the PRIO_PROCESS, PRIO_MIN, and PRIO_MAX constants
65 from your system, as well as the getpriority() and setpriority() system
66 calls. Here's the preamble of the class.
72 $Nice::DEBUG = 0 unless defined $Nice::DEBUG;
76 =item TIESCALAR classname, LIST
78 This is the constructor for the class. That means it is
79 expected to return a blessed reference to a new scalar
80 (probably anonymous) that it's creating. For example:
84 my $pid = shift || $$; # 0 means me
86 if ($pid !~ /^\d+$/) {
87 carp "Nice::Tie::Scalar got non-numeric pid $pid" if $^W;
91 unless (kill 0, $pid) { # EPERM or ERSCH, no doubt
92 carp "Nice::Tie::Scalar got bad pid $pid: $!" if $^W;
96 return bless \$pid, $class;
99 This tie class has chosen to return an error rather than raising an
100 exception if its constructor should fail. While this is how dbmopen() works,
101 other classes may well not wish to be so forgiving. It checks the global
102 variable C<$^W> to see whether to emit a bit of noise anyway.
106 This method will be triggered every time the tied variable is accessed
107 (read). It takes no arguments beyond its self reference, which is the
108 object representing the scalar we're dealing with. Because in this case
109 we're using just a SCALAR ref for the tied scalar object, a simple $$self
110 allows the method to get at the real value stored there. In our example
111 below, that real value is the process ID to which we've tied our variable.
115 confess "wrong type" unless ref $self;
116 croak "usage error" if @_;
119 $nicety = getpriority(PRIO_PROCESS, $$self);
120 if ($!) { croak "getpriority failed: $!" }
124 This time we've decided to blow up (raise an exception) if the renice
125 fails--there's no place for us to return an error otherwise, and it's
126 probably the right thing to do.
128 =item STORE this, value
130 This method will be triggered every time the tied variable is set
131 (assigned). Beyond its self reference, it also expects one (and only one)
132 argument--the new value the user is trying to assign.
136 confess "wrong type" unless ref $self;
137 my $new_nicety = shift;
138 croak "usage error" if @_;
140 if ($new_nicety < PRIO_MIN) {
142 "WARNING: priority %d less than minimum system priority %d",
143 $new_nicety, PRIO_MIN if $^W;
144 $new_nicety = PRIO_MIN;
147 if ($new_nicety > PRIO_MAX) {
149 "WARNING: priority %d greater than maximum system priority %d",
150 $new_nicety, PRIO_MAX if $^W;
151 $new_nicety = PRIO_MAX;
154 unless (defined setpriority(PRIO_PROCESS, $$self, $new_nicety)) {
155 confess "setpriority failed: $!";
162 This method will be triggered when the C<untie> occurs. This can be useful
163 if the class needs to know when no further calls will be made. (Except DESTROY
164 of course.) See below for more details.
168 This method will be triggered when the tied variable needs to be destructed.
169 As with other object classes, such a method is seldom necessary, because Perl
170 deallocates its moribund object's memory for you automatically--this isn't
171 C++, you know. We'll use a DESTROY method here for debugging purposes only.
175 confess "wrong type" unless ref $self;
176 carp "[ Nice::DESTROY pid $$self ]" if $Nice::DEBUG;
181 That's about all there is to it. Actually, it's more than all there
182 is to it, because we've done a few nice things here for the sake
183 of completeness, robustness, and general aesthetics. Simpler
184 TIESCALAR classes are certainly possible.
188 A class implementing a tied ordinary array should define the following
189 methods: TIEARRAY, FETCH, STORE, FETCHSIZE, STORESIZE and perhaps UNTIE and/or DESTROY.
191 FETCHSIZE and STORESIZE are used to provide C<$#array> and
192 equivalent C<scalar(@array)> access.
194 The methods POP, PUSH, SHIFT, UNSHIFT, SPLICE, DELETE, and EXISTS are
195 required if the perl operator with the corresponding (but lowercase) name
196 is to operate on the tied array. The B<Tie::Array> class can be used as a
197 base class to implement the first five of these in terms of the basic
198 methods above. The default implementations of DELETE and EXISTS in
199 B<Tie::Array> simply C<croak>.
201 In addition EXTEND will be called when perl would have pre-extended
202 allocation in a real array.
204 This means that tied arrays are now I<complete>. The example below needs
205 upgrading to illustrate this. (The documentation in B<Tie::Array> is more
208 For this discussion, we'll implement an array whose indices are fixed at
209 its creation. If you try to access anything beyond those bounds, you'll
210 take an exception. For example:
212 require Bounded_Array;
213 tie @ary, 'Bounded_Array', 2;
216 print "setting index $i: ";
219 print "value of elt $i now $ary[$i]\n";
222 The preamble code for the class is as follows:
224 package Bounded_Array;
230 =item TIEARRAY classname, LIST
232 This is the constructor for the class. That means it is expected to
233 return a blessed reference through which the new array (probably an
234 anonymous ARRAY ref) will be accessed.
236 In our example, just to show you that you don't I<really> have to return an
237 ARRAY reference, we'll choose a HASH reference to represent our object.
238 A HASH works out well as a generic record type: the C<{BOUND}> field will
239 store the maximum bound allowed, and the C<{ARRAY}> field will hold the
240 true ARRAY ref. If someone outside the class tries to dereference the
241 object returned (doubtless thinking it an ARRAY ref), they'll blow up.
242 This just goes to show you that you should respect an object's privacy.
247 confess "usage: tie(\@ary, 'Bounded_Array', max_subscript)"
248 if @_ || $bound =~ /\D/;
255 =item FETCH this, index
257 This method will be triggered every time an individual element the tied array
258 is accessed (read). It takes one argument beyond its self reference: the
259 index whose value we're trying to fetch.
263 if ($idx > $self->{BOUND}) {
264 confess "Array OOB: $idx > $self->{BOUND}";
266 return $self->{ARRAY}[$idx];
269 If a negative array index is used to read from an array, the index
270 will be translated to a positive one internally by calling FETCHSIZE
271 before being passed to FETCH.
273 As you may have noticed, the name of the FETCH method (et al.) is the same
274 for all accesses, even though the constructors differ in names (TIESCALAR
275 vs TIEARRAY). While in theory you could have the same class servicing
276 several tied types, in practice this becomes cumbersome, and it's easiest
277 to keep them at simply one tie type per class.
279 =item STORE this, index, value
281 This method will be triggered every time an element in the tied array is set
282 (written). It takes two arguments beyond its self reference: the index at
283 which we're trying to store something and the value we're trying to put
287 my($self, $idx, $value) = @_;
288 print "[STORE $value at $idx]\n" if _debug;
289 if ($idx > $self->{BOUND} ) {
290 confess "Array OOB: $idx > $self->{BOUND}";
292 return $self->{ARRAY}[$idx] = $value;
295 Negative indexes are treated the same as with FETCH.
299 Will be called when C<untie> happens. (See below.)
303 This method will be triggered when the tied variable needs to be destructed.
304 As with the scalar tie class, this is almost never needed in a
305 language that does its own garbage collection, so this time we'll
310 The code we presented at the top of the tied array class accesses many
311 elements of the array, far more than we've set the bounds to. Therefore,
312 it will blow up once they try to access beyond the 2nd element of @ary, as
313 the following output demonstrates:
315 setting index 0: value of elt 0 now 0
316 setting index 1: value of elt 1 now 10
317 setting index 2: value of elt 2 now 20
318 setting index 3: Array OOB: 3 > 2 at Bounded_Array.pm line 39
319 Bounded_Array::FETCH called at testba line 12
323 Hashes were the first Perl data type to be tied (see dbmopen()). A class
324 implementing a tied hash should define the following methods: TIEHASH is
325 the constructor. FETCH and STORE access the key and value pairs. EXISTS
326 reports whether a key is present in the hash, and DELETE deletes one.
327 CLEAR empties the hash by deleting all the key and value pairs. FIRSTKEY
328 and NEXTKEY implement the keys() and each() functions to iterate over all
329 the keys. UNTIE is called when C<untie> happens, and DESTROY is called when
330 the tied variable is garbage collected.
332 If this seems like a lot, then feel free to inherit from merely the
333 standard Tie::Hash module for most of your methods, redefining only the
334 interesting ones. See L<Tie::Hash> for details.
336 Remember that Perl distinguishes between a key not existing in the hash,
337 and the key existing in the hash but having a corresponding value of
338 C<undef>. The two possibilities can be tested with the C<exists()> and
339 C<defined()> functions.
341 Here's an example of a somewhat interesting tied hash class: it gives you
342 a hash representing a particular user's dot files. You index into the hash
343 with the name of the file (minus the dot) and you get back that dot file's
344 contents. For example:
347 tie %dot, 'DotFiles';
348 if ( $dot{profile} =~ /MANPATH/ ||
349 $dot{login} =~ /MANPATH/ ||
350 $dot{cshrc} =~ /MANPATH/ )
352 print "you seem to set your MANPATH\n";
355 Or here's another sample of using our tied class:
357 tie %him, 'DotFiles', 'daemon';
358 foreach $f ( keys %him ) {
359 printf "daemon dot file %s is size %d\n",
363 In our tied hash DotFiles example, we use a regular
364 hash for the object containing several important
365 fields, of which only the C<{LIST}> field will be what the
366 user thinks of as the real hash.
372 whose dot files this object represents
376 where those dot files live
380 whether we should try to change or remove those dot files
384 the hash of dot file names and content mappings
388 Here's the start of F<Dotfiles.pm>:
392 sub whowasi { (caller(1))[3] . '()' }
394 sub debug { $DEBUG = @_ ? shift : 1 }
396 For our example, we want to be able to emit debugging info to help in tracing
397 during development. We keep also one convenience function around
398 internally to help print out warnings; whowasi() returns the function name
401 Here are the methods for the DotFiles tied hash.
405 =item TIEHASH classname, LIST
407 This is the constructor for the class. That means it is expected to
408 return a blessed reference through which the new object (probably but not
409 necessarily an anonymous hash) will be accessed.
411 Here's the constructor:
415 my $user = shift || $>;
416 my $dotdir = shift || '';
417 croak "usage: @{[&whowasi]} [USER [DOTDIR]]" if @_;
418 $user = getpwuid($user) if $user =~ /^\d+$/;
419 my $dir = (getpwnam($user))[7]
420 || croak "@{[&whowasi]}: no user $user";
421 $dir .= "/$dotdir" if $dotdir;
431 || croak "@{[&whowasi]}: can't opendir $dir: $!";
432 foreach $dot ( grep /^\./ && -f "$dir/$_", readdir(DIR)) {
434 $node->{LIST}{$dot} = undef;
437 return bless $node, $self;
440 It's probably worth mentioning that if you're going to filetest the
441 return values out of a readdir, you'd better prepend the directory
442 in question. Otherwise, because we didn't chdir() there, it would
443 have been testing the wrong file.
445 =item FETCH this, key
447 This method will be triggered every time an element in the tied hash is
448 accessed (read). It takes one argument beyond its self reference: the key
449 whose value we're trying to fetch.
451 Here's the fetch for our DotFiles example.
454 carp &whowasi if $DEBUG;
457 my $dir = $self->{HOME};
458 my $file = "$dir/.$dot";
460 unless (exists $self->{LIST}->{$dot} || -f $file) {
461 carp "@{[&whowasi]}: no $dot file" if $DEBUG;
465 if (defined $self->{LIST}->{$dot}) {
466 return $self->{LIST}->{$dot};
468 return $self->{LIST}->{$dot} = `cat $dir/.$dot`;
472 It was easy to write by having it call the Unix cat(1) command, but it
473 would probably be more portable to open the file manually (and somewhat
474 more efficient). Of course, because dot files are a Unixy concept, we're
477 =item STORE this, key, value
479 This method will be triggered every time an element in the tied hash is set
480 (written). It takes two arguments beyond its self reference: the index at
481 which we're trying to store something, and the value we're trying to put
484 Here in our DotFiles example, we'll be careful not to let
485 them try to overwrite the file unless they've called the clobber()
486 method on the original object reference returned by tie().
489 carp &whowasi if $DEBUG;
493 my $file = $self->{HOME} . "/.$dot";
494 my $user = $self->{USER};
496 croak "@{[&whowasi]}: $file not clobberable"
497 unless $self->{CLOBBER};
499 open(F, "> $file") || croak "can't open $file: $!";
504 If they wanted to clobber something, they might say:
506 $ob = tie %daemon_dots, 'daemon';
508 $daemon_dots{signature} = "A true daemon\n";
510 Another way to lay hands on a reference to the underlying object is to
511 use the tied() function, so they might alternately have set clobber
514 tie %daemon_dots, 'daemon';
515 tied(%daemon_dots)->clobber(1);
517 The clobber method is simply:
521 $self->{CLOBBER} = @_ ? shift : 1;
524 =item DELETE this, key
526 This method is triggered when we remove an element from the hash,
527 typically by using the delete() function. Again, we'll
528 be careful to check whether they really want to clobber files.
531 carp &whowasi if $DEBUG;
535 my $file = $self->{HOME} . "/.$dot";
536 croak "@{[&whowasi]}: won't remove file $file"
537 unless $self->{CLOBBER};
538 delete $self->{LIST}->{$dot};
539 my $success = unlink($file);
540 carp "@{[&whowasi]}: can't unlink $file: $!" unless $success;
544 The value returned by DELETE becomes the return value of the call
545 to delete(). If you want to emulate the normal behavior of delete(),
546 you should return whatever FETCH would have returned for this key.
547 In this example, we have chosen instead to return a value which tells
548 the caller whether the file was successfully deleted.
552 This method is triggered when the whole hash is to be cleared, usually by
553 assigning the empty list to it.
555 In our example, that would remove all the user's dot files! It's such a
556 dangerous thing that they'll have to set CLOBBER to something higher than
560 carp &whowasi if $DEBUG;
562 croak "@{[&whowasi]}: won't remove all dot files for $self->{USER}"
563 unless $self->{CLOBBER} > 1;
565 foreach $dot ( keys %{$self->{LIST}}) {
570 =item EXISTS this, key
572 This method is triggered when the user uses the exists() function
573 on a particular hash. In our example, we'll look at the C<{LIST}>
574 hash element for this:
577 carp &whowasi if $DEBUG;
580 return exists $self->{LIST}->{$dot};
585 This method will be triggered when the user is going
586 to iterate through the hash, such as via a keys() or each()
590 carp &whowasi if $DEBUG;
592 my $a = keys %{$self->{LIST}}; # reset each() iterator
593 each %{$self->{LIST}}
596 =item NEXTKEY this, lastkey
598 This method gets triggered during a keys() or each() iteration. It has a
599 second argument which is the last key that had been accessed. This is
600 useful if you're carrying about ordering or calling the iterator from more
601 than one sequence, or not really storing things in a hash anywhere.
603 For our example, we're using a real hash so we'll do just the simple
604 thing, but we'll have to go through the LIST field indirectly.
607 carp &whowasi if $DEBUG;
609 return each %{ $self->{LIST} }
614 This is called when C<untie> occurs.
618 This method is triggered when a tied hash is about to go out of
619 scope. You don't really need it unless you're trying to add debugging
620 or have auxiliary state to clean up. Here's a very simple function:
623 carp &whowasi if $DEBUG;
628 Note that functions such as keys() and values() may return huge lists
629 when used on large objects, like DBM files. You may prefer to use the
630 each() function to iterate over such. Example:
632 # print out history file offsets
634 tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
635 while (($key,$val) = each %HIST) {
636 print $key, ' = ', unpack('L',$val), "\n";
640 =head2 Tying FileHandles
642 This is partially implemented now.
644 A class implementing a tied filehandle should define the following
645 methods: TIEHANDLE, at least one of PRINT, PRINTF, WRITE, READLINE, GETC,
646 READ, and possibly CLOSE, UNTIE and DESTROY. The class can also provide: BINMODE,
647 OPEN, EOF, FILENO, SEEK, TELL - if the corresponding perl operators are
650 It is especially useful when perl is embedded in some other program,
651 where output to STDOUT and STDERR may have to be redirected in some
652 special way. See nvi and the Apache module for examples.
654 In our example we're going to create a shouting handle.
660 =item TIEHANDLE classname, LIST
662 This is the constructor for the class. That means it is expected to
663 return a blessed reference of some sort. The reference can be used to
664 hold some internal information.
666 sub TIEHANDLE { print "<shout>\n"; my $i; bless \$i, shift }
668 =item WRITE this, LIST
670 This method will be called when the handle is written to via the
671 C<syswrite> function.
675 my($buf,$len,$offset) = @_;
676 print "WRITE called, \$buf=$buf, \$len=$len, \$offset=$offset";
679 =item PRINT this, LIST
681 This method will be triggered every time the tied handle is printed to
682 with the C<print()> function.
683 Beyond its self reference it also expects the list that was passed to
686 sub PRINT { $r = shift; $$r++; print join($,,map(uc($_),@_)),$\ }
688 =item PRINTF this, LIST
690 This method will be triggered every time the tied handle is printed to
691 with the C<printf()> function.
692 Beyond its self reference it also expects the format and list that was
693 passed to the printf function.
698 print sprintf($fmt, @_)."\n";
701 =item READ this, LIST
703 This method will be called when the handle is read from via the C<read>
704 or C<sysread> functions.
708 my $$bufref = \$_[0];
709 my(undef,$len,$offset) = @_;
710 print "READ called, \$buf=$bufref, \$len=$len, \$offset=$offset";
711 # add to $$bufref, set $len to number of characters read
717 This method will be called when the handle is read from via <HANDLE>.
718 The method should return undef when there is no more data.
720 sub READLINE { $r = shift; "READLINE called $$r times\n"; }
724 This method will be called when the C<getc> function is called.
726 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
730 This method will be called when the handle is closed via the C<close>
733 sub CLOSE { print "CLOSE called.\n" }
737 As with the other types of ties, this method will be called when C<untie> happens.
738 It may be appropriate to "auto CLOSE" when this occurs.
742 As with the other types of ties, this method will be called when the
743 tied handle is about to be destroyed. This is useful for debugging and
744 possibly cleaning up.
746 sub DESTROY { print "</shout>\n" }
750 Here's how to use our little example:
755 print FOO $a, " plus ", $b, " equals ", $a + $b, "\n";
760 You can define for all tie types an UNTIE method that will be called
763 =head2 The C<untie> Gotcha
765 If you intend making use of the object returned from either tie() or
766 tied(), and if the tie's target class defines a destructor, there is a
767 subtle gotcha you I<must> guard against.
769 As setup, consider this (admittedly rather contrived) example of a
770 tie; all it does is use a file to keep a log of the values assigned to
781 my $filename = shift;
782 my $handle = new IO::File "> $filename"
783 or die "Cannot open $filename: $!\n";
785 print $handle "The Start\n";
786 bless {FH => $handle, Value => 0}, $class;
791 return $self->{Value};
797 my $handle = $self->{FH};
798 print $handle "$value\n";
799 $self->{Value} = $value;
804 my $handle = $self->{FH};
805 print $handle "The End\n";
811 Here is an example that makes use of this tie:
817 tie $fred, 'Remember', 'myfile.txt';
822 system "cat myfile.txt";
824 This is the output when it is executed:
832 So far so good. Those of you who have been paying attention will have
833 spotted that the tied object hasn't been used so far. So lets add an
834 extra method to the Remember class to allow comments to be included in
835 the file -- say, something like this:
840 my $handle = $self->{FH};
841 print $handle $text, "\n";
844 And here is the previous example modified to use the C<comment> method
845 (which requires the tied object):
851 $x = tie $fred, 'Remember', 'myfile.txt';
854 comment $x "changing...";
857 system "cat myfile.txt";
859 When this code is executed there is no output. Here's why:
861 When a variable is tied, it is associated with the object which is the
862 return value of the TIESCALAR, TIEARRAY, or TIEHASH function. This
863 object normally has only one reference, namely, the implicit reference
864 from the tied variable. When untie() is called, that reference is
865 destroyed. Then, as in the first example above, the object's
866 destructor (DESTROY) is called, which is normal for objects that have
867 no more valid references; and thus the file is closed.
869 In the second example, however, we have stored another reference to
870 the tied object in $x. That means that when untie() gets called
871 there will still be a valid reference to the object in existence, so
872 the destructor is not called at that time, and thus the file is not
873 closed. The reason there is no output is because the file buffers
874 have not been flushed to disk.
876 Now that you know what the problem is, what can you do to avoid it?
877 Prior to the introduction of the optional UNTIE method the only way
878 was the good old C<-w> flag. Which will spot any instances where you call
879 untie() and there are still valid references to the tied object. If
880 the second script above this near the top C<use warnings 'untie'>
881 or was run with the C<-w> flag, Perl prints this
884 untie attempted while 1 inner references still exist
886 To get the script to work properly and silence the warning make sure
887 there are no valid references to the tied object I<before> untie() is
893 Now that UNTIE exists the class designer can decide which parts of the
894 class functionality are really associated with C<untie> and which with
895 the object being destroyed. What makes sense for a given class depends
896 on whether the inner references are being kept so that non-tie-related
897 methods can be called on the object. But in most cases it probably makes
898 sense to move the functionality that would have been in DESTROY to the UNTIE
901 If the UNTIE method exists then the warning above does not occur. Instead the
902 UNTIE method is passed the count of "extra" references and can issue its own
903 warning if appropriate. e.g. to replicate the no UNTIE case this method can
908 my ($obj,$count) = @_;
909 carp "untie attempted while $count inner references still exist" if $count;
914 See L<DB_File> or L<Config> for some interesting tie() implementations.
915 A good starting point for many tie() implementations is with one of the
916 modules L<Tie::Scalar>, L<Tie::Array>, L<Tie::Hash>, or L<Tie::Handle>.
920 You cannot easily tie a multilevel data structure (such as a hash of
921 hashes) to a dbm file. The first problem is that all but GDBM and
922 Berkeley DB have size limitations, but beyond that, you also have problems
923 with how references are to be represented on disk. One experimental
924 module that does attempt to address this need partially is the MLDBM
925 module. Check your nearest CPAN site as described in L<perlmodlib> for
926 source code to MLDBM.
928 Tied filehandles are still incomplete. sysopen(), truncate(),
929 flock(), fcntl(), stat() and -X can't currently be trapped.
935 TIEHANDLE by Sven Verdoolaege <F<skimo@dns.ufsia.ac.be>> and Doug MacEachern <F<dougm@osf.org>>
937 UNTIE by Nick Ing-Simmons <F<nick@ing-simmons.net>>