summaryrefslogtreecommitdiff
path: root/Master/tlpkg/tlperl/lib/Tie/Watch.pm
blob: 48f46acd2b0a0de8dba279486123fac89a099e6c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
$Tie::Watch::VERSION = '1.2';

package Tie::Watch;

=head1 NAME

 Tie::Watch - place watchpoints on Perl variables.

=head1 SYNOPSIS

 use Tie::Watch;

 $watch = Tie::Watch->new(
     -variable => \$frog,
     -debug    => 1,
     -shadow   => 0,			  
     -fetch    => [\&fetch, 'arg1', 'arg2', ..., 'argn'],
     -store    => \&store,
     -destroy  => sub {print "Final value=$frog.\n"},
 }
 %vinfo = $watch->Info;
 $args  = $watch->Args(-fetch);
 $val   = $watch->Fetch;
 print "val=", $watch->Say($val), ".\n";
 $watch->Store('Hello');
 $watch->Unwatch;

=head1 DESCRIPTION

This class module binds one or more subroutines of your devising to a
Perl variable.  All variables can have B<FETCH>, B<STORE> and
B<DESTROY> callbacks.  Additionally, arrays can define B<CLEAR>,
B<DELETE>, B<EXISTS>, B<EXTEND>, B<FETCHSIZE>, B<POP>, B<PUSH>,
B<SHIFT>, B<SPLICE>, B<STORESIZE> and B<UNSHIFT> callbacks, and hashes
can define B<CLEAR>, B<DELETE>, B<EXISTS>, B<FIRSTKEY> and B<NEXTKEY>
callbacks.  If these term are unfamiliar to you, I I<really> suggest
you read L<perltie>.

With Tie::Watch you can:

 . alter a variable's value
 . prevent a variable's value from being changed
 . invoke a Perl/Tk callback when a variable changes
 . trace references to a variable

Callback format is patterned after the Perl/Tk scheme: supply either a
code reference, or, supply an array reference and pass the callback
code reference in the first element of the array, followed by callback
arguments.  (See examples in the Synopsis, above.)

Tie::Watch provides default callbacks for any that you fail to
specify.  Other than negatively impacting performance, they perform
the standard action that you'd expect, so the variable behaves
"normally".  Once you override a default callback, perhaps to insert
debug code like print statements, your callback normally finishes by
calling the underlying (overridden) method.  But you don't have to!

To map a tied method name to a default callback name simply lowercase
the tied method name and uppercase its first character.  So FETCH
becomes Fetch, NEXTKEY becomes Nextkey, etcetera.

Here are two callbacks for a scalar. The B<FETCH> (read) callback does
nothing other than illustrate the fact that it returns the value to
assign the variable.  The B<STORE> (write) callback uppercases the
variable and returns it.  In all cases the callback I<must> return the
correct read or write value - typically, it does this by invoking the
underlying method.

 my $fetch_scalar = sub {
     my($self) = @_;
     $self->Fetch;
 };

 my $store_scalar = sub {
     my($self, $new_val) = @_;
     $self->Store(uc $new_val);
 };

Here are B<FETCH> and B<STORE> callbacks for either an array or hash.
They do essentially the same thing as the scalar callbacks, but
provide a little more information.

 my $fetch = sub {
     my($self, $key) = @_;
     my $val = $self->Fetch($key);
     print "In fetch callback, key=$key, val=", $self->Say($val);
     my $args = $self->Args(-fetch);
     print ", args=('", join("', '",  @$args), "')" if $args;
     print ".\n";
     $val;
 };

 my $store = sub {
     my($self, $key, $new_val) = @_;
     my $val = $self->Fetch($key);
     $new_val = uc $new_val;
     $self->Store($key, $new_val);
     print "In store callback, key=$key, val=", $self->Say($val),
       ", new_val=", $self->Say($new_val);
     my $args = $self->Args(-store);
     print ", args=('", join("', '",  @$args), "')" if $args;
     print ".\n";
     $new_val;
 };

In all cases, the first parameter is a reference to the Watch object,
used to invoke the following class methods.

=head1 METHODS

=over 4

=item $watch = Tie::Watch->new(-options => values);

The watchpoint constructor method that accepts option/value pairs to
create and configure the Watch object.  The only required option is
B<-variable>.

B<-variable> is a I<reference> to a scalar, array or hash variable.

B<-debug> (default 0) is 1 to activate debug print statements internal
to Tie::Watch.

B<-shadow> (default 1) is 0 to disable array and hash shadowing.  To
prevent infinite recursion Tie::Watch maintains parallel variables for
arrays and hashes.  When the watchpoint is created the parallel shadow
variable is initialized with the watched variable's contents, and when
the watchpoint is deleted the shadow variable is copied to the original
variable.  Thus, changes made during the watch process are not lost.
Shadowing is on my default.  If you disable shadowing any changes made
to an array or hash are lost when the watchpoint is deleted.

Specify any of the following relevant callback parameters, in the
format described above: B<-fetch>, B<-store>, B<-destroy>.
Additionally for arrays: B<-clear>, B<-extend>, B<-fetchsize>,
B<-pop>, B<-push>, B<-shift>, B<-splice>, B<-storesize> and
B<-unshift>.  Additionally for hashes: B<-clear>, B<-delete>,
B<-exists>, B<-firstkey> and B<-nextkey>.

=item $args = $watch->Args(-fetch);

Returns a reference to a list of arguments for the specified callback,
or undefined if none.

=item $watch->Fetch();  $watch->Fetch($key);

Returns a variable's current value.  $key is required for an array or
hash.

=item %vinfo = $watch->Info();

Returns a hash detailing the internals of the Watch object, with these
keys:

 %vinfo = {
     -variable =>  SCALAR(0x200737f8)
     -debug    =>  '0'
     -shadow   =>  '1'
     -value    =>  'HELLO SCALAR'
     -destroy  =>  ARRAY(0x200f86cc)
     -fetch    =>  ARRAY(0x200f8558)
     -store    =>  ARRAY(0x200f85a0)
     -legible  =>  above data formatted as a list of string, for printing
 }

For array and hash Watch objects, the B<-value> key is replaced with a
B<-ptr> key which is a reference to the parallel array or hash.
Additionally, for an array or hash, there are key/value pairs for
all the variable specific callbacks.

=item $watch->Say($val);

Used mainly for debugging, it returns $val in quotes if required, or
the string "undefined" for undefined values.

=item $watch->Store($new_val);  $watch->Store($key, $new_val);

Store a variable's new value.  $key is required for an array or hash.

=item $watch->Unwatch();

Stop watching the variable.

=back

=head1 EFFICIENCY CONSIDERATIONS

If you can live using the class methods provided, please do so.  You
can meddle with the object hash directly and improved watch
performance, at the risk of your code breaking in the future.

=head1 AUTHOR

Stephen O. Lidie

=head1 HISTORY

 lusol@Lehigh.EDU, LUCC, 96/05/30
 . Original version 0.92 release, based on the Trace module from Hans Mulder,
   and ideas from Tim Bunce.

 lusol@Lehigh.EDU, LUCC, 96/12/25
 . Version 0.96, release two inner references detected by Perl 5.004.

 lusol@Lehigh.EDU, LUCC, 97/01/11
 . Version 0.97, fix Makefile.PL and MANIFEST (thanks Andreas Koenig).
   Make sure test.pl doesn't fail if Tk isn't installed.

 Stephen.O.Lidie@Lehigh.EDU, Lehigh University Computing Center, 97/10/03
 . Version 0.98, implement -shadow option for arrays and hashes.

 Stephen.O.Lidie@Lehigh.EDU, Lehigh University Computing Center, 98/02/11
 . Version 0.99, finally, with Perl 5.004_57, we can completely watch arrays.
   With tied array support this module is essentially complete, so its been
   optimized for speed at the expense of clarity - sorry about that. The
   Delete() method has been renamed Unwatch() because it conflicts with the
   builtin delete().

 Stephen.O.Lidie@Lehigh.EDU, Lehigh University Computing Center, 99/04/04
 . Version 1.0, for Perl 5.005_03, update Makefile.PL for ActiveState, and
   add two examples (one for Perl/Tk).

 sol0@lehigh.edu, Lehigh University Computing Center, 2003/06/07
 . Version 1.1, for Perl 5.8, can trace a reference now, patch from Slaven
   Rezic.

 sol0@lehigh.edu, Lehigh University Computing Center, 2005/05/17
 . Version 1.2, for Perl 5.8, per Rob Seegel's suggestion, support array
   DELETE and EXISTS.

=head1 COPYRIGHT

Copyright (C) 1996 - 2005 Stephen O. Lidie. All rights reserved.

This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.

=cut

use 5.004_57;;
use Carp;
use strict;
use subs qw/normalize_callbacks/;
use vars qw/@array_callbacks @hash_callbacks @scalar_callbacks/;

@array_callbacks  = qw/-clear -delete -destroy -exists -extend -fetch
                       -fetchsize -pop -push -shift -splice -store
                       -storesize -unshift/;
@hash_callbacks   = qw/-clear -delete -destroy -exists -fetch -firstkey 
                       -nextkey -store/;
@scalar_callbacks = qw/-destroy -fetch -store/;

sub new {

    # Watch constructor.  The *real* constructor is Tie::Watch->base_watch(),
    # invoked by methods in other Watch packages, depending upon the variable's
    # type.  Here we supply defaulted parameter values and then verify them,
    # normalize all callbacks and bind the variable to the appropriate package.

    my($class, %args) = @_;
    my $version = $Tie::Watch::VERSION;
    my (%arg_defaults) = (-debug => 0, -shadow  => 1);
    my $variable = $args{-variable};
    croak "Tie::Watch::new(): -variable is required." if not defined $variable;

    my($type, $watch_obj) = (ref $variable, undef);
    if ($type =~ /(SCALAR|REF)/) {
	@arg_defaults{@scalar_callbacks} = (
	    [\&Tie::Watch::Scalar::Destroy],  [\&Tie::Watch::Scalar::Fetch],
	    [\&Tie::Watch::Scalar::Store]);
    } elsif ($type =~ /ARRAY/) {
	@arg_defaults{@array_callbacks}  = (
	    [\&Tie::Watch::Array::Clear],     [\&Tie::Watch::Array::Delete],
	    [\&Tie::Watch::Array::Destroy],   [\&Tie::Watch::Array::Exists],
	    [\&Tie::Watch::Array::Extend],    [\&Tie::Watch::Array::Fetch],
	    [\&Tie::Watch::Array::Fetchsize], [\&Tie::Watch::Array::Pop],
            [\&Tie::Watch::Array::Push],      [\&Tie::Watch::Array::Shift],
            [\&Tie::Watch::Array::Splice],    [\&Tie::Watch::Array::Store],
            [\&Tie::Watch::Array::Storesize], [\&Tie::Watch::Array::Unshift]);
    } elsif ($type =~ /HASH/) {
	@arg_defaults{@hash_callbacks}   = (
	    [\&Tie::Watch::Hash::Clear],      [\&Tie::Watch::Hash::Delete],
	    [\&Tie::Watch::Hash::Destroy],    [\&Tie::Watch::Hash::Exists],
            [\&Tie::Watch::Hash::Fetch],      [\&Tie::Watch::Hash::Firstkey],
            [\&Tie::Watch::Hash::Nextkey],    [\&Tie::Watch::Hash::Store]);
    } else {
	croak "Tie::Watch::new() - not a variable reference.";
    }
    my(@margs, %ahsh, $args, @args);
    @margs = grep ! defined $args{$_}, keys %arg_defaults;
    %ahsh = %args;                         # argument hash
    @ahsh{@margs} = @arg_defaults{@margs}; # fill in missing values
    normalize_callbacks \%ahsh;

    if ($type =~ /(SCALAR|REF)/) {
        $watch_obj = tie $$variable, 'Tie::Watch::Scalar', %ahsh;
    } elsif ($type =~ /ARRAY/) {
        $watch_obj = tie @$variable, 'Tie::Watch::Array',  %ahsh;
    } elsif ($type =~ /HASH/) {
        $watch_obj = tie %$variable, 'Tie::Watch::Hash',   %ahsh;
    }
    $watch_obj;

} # end new, Watch constructor

sub Args {

    # Return a reference to a list of callback arguments, or undef if none.
    #
    # $_[0] = self
    # $_[1] = callback type

    defined $_[0]->{$_[1]}->[1] ? [@{$_[0]->{$_[1]}}[1 .. $#{$_[0]->{$_[1]}}]]
	: undef;

} # end Args

sub Info {

    # Info() method subclassed by other Watch modules.
    #
    # $_[0] = self
    # @_[1 .. $#_] = optional callback types

    my(%vinfo, @results);
    my(@info) = (qw/-variable -debug -shadow/);
    push @info, @_[1 .. $#_] if scalar @_ >= 2;
    foreach my $type (@info) {
	push @results, 	sprintf('%-10s: ', substr $type, 1) .
	    $_[0]->Say($_[0]->{$type});
	$vinfo{$type} = $_[0]->{$type};
    }
    $vinfo{-legible} = [@results];
    %vinfo;

} # end Info

sub Say {

    # For debugging, mainly.
    #
    # $_[0] = self
    # $_[1] = value

    defined $_[1] ? (ref($_[1]) ne '' ? $_[1] : "'$_[1]'") : "undefined";

} # end Say

sub Unwatch {

    # Stop watching a variable by releasing the last reference and untieing it.
    # Update the original variable with its shadow, if appropriate.
    #
    # $_[0] = self

    my $variable = $_[0]->{-variable};
    my $type = ref $variable;
    my $copy = $_[0]->{-ptr} if $type !~ /(SCALAR|REF)/;
    my $shadow = $_[0]->{-shadow};
    undef $_[0];
    if ($type =~ /(SCALAR|REF)/) {
	untie $$variable;
    } elsif ($type =~ /ARRAY/) {
	untie @$variable;
	@$variable = @$copy if $shadow;
    } elsif ($type =~ /HASH/) {
	untie %$variable;
	%$variable = %$copy if $shadow;
    } else {
	croak "Tie::Watch::Delete() - not a variable reference.";
    }

} # end Unwatch

# Watch private methods.

sub base_watch {

    # Watch base class constructor invoked by other Watch modules.

    my($class, %args) = @_;
    my $watch_obj = {%args}; 
    $watch_obj;

} # end base_watch

sub callback {
    
    # Execute a Watch callback, either the default or user specified.
    # Note that the arguments are those supplied by the tied method,
    # not those (if any) specified by the user when the watch object
    # was instantiated.  This is for performance reasons, and why the
    # Args() method exists.
    #
    # $_[0] = self
    # $_[1] = callback type
    # $_[2] through $#_ = tied arguments

    &{$_[0]->{$_[1]}->[0]} ($_[0], @_[2 .. $#_]);

} # end callback

sub normalize_callbacks {

    # Ensure all callbacks are normalized in [\&code, @args] format.

    my($args_ref) = @_;
    my($cb, $ref);
    foreach my $arg (keys %$args_ref) {
	next if $arg =~ /variable|debug|shadow/;
	$cb = $args_ref->{$arg};
	$ref = ref $cb;
	if ($ref =~ /CODE/) {
	    $args_ref->{$arg} = [$cb];
	} elsif ($ref !~ /ARRAY/) {
	    croak "Tie::Watch:  malformed callback $arg=$cb.";
	}
    }

} # end normalize_callbacks

###############################################################################

package Tie::Watch::Scalar;

use Carp;
@Tie::Watch::Scalar::ISA = qw/Tie::Watch/;

sub TIESCALAR {

    my($class, %args) = @_;
    my $variable = $args{-variable};
    my $watch_obj = Tie::Watch->base_watch(%args);
    $watch_obj->{-value} = $$variable;
    print "WatchScalar new: $variable created, \@_=", join(',', @_), "!\n"
	if $watch_obj->{-debug};
    bless $watch_obj, $class;

} # end TIESCALAR

sub Info {$_[0]->SUPER::Info('-value', @Tie::Watch::scalar_callbacks)}

# Default scalar callbacks.

sub Destroy {undef %{$_[0]}}
sub Fetch   {$_[0]->{-value}}
sub Store   {$_[0]->{-value} = $_[1]}

# Scalar access methods.

sub DESTROY {$_[0]->callback('-destroy')}
sub FETCH   {$_[0]->callback('-fetch')}
sub STORE   {$_[0]->callback('-store', $_[1])}

###############################################################################

package Tie::Watch::Array;

use Carp;
@Tie::Watch::Array::ISA = qw/Tie::Watch/;

sub TIEARRAY {

    my($class, %args) = @_;
    my($variable, $shadow) = @args{-variable, -shadow};
    my @copy = @$variable if $shadow; # make a private copy of user's array
    $args{-ptr} = $shadow ? \@copy : [];
    my $watch_obj = Tie::Watch->base_watch(%args);
    print "WatchArray new: $variable created, \@_=", join(',', @_), "!\n"
	if $watch_obj->{-debug};
    bless $watch_obj, $class;

} # end TIEARRAY

sub Info {$_[0]->SUPER::Info('-ptr', @Tie::Watch::array_callbacks)}

# Default array callbacks.

sub Clear     {$_[0]->{-ptr} = ()}
sub Delete    {delete $_[0]->{-ptr}->[$_[1]]}
sub Destroy   {undef %{$_[0]}}
sub Exists    {exists $_[0]->{-ptr}->[$_[1]]}
sub Extend    {}
sub Fetch     {$_[0]->{-ptr}->[$_[1]]}
sub Fetchsize {scalar @{$_[0]->{-ptr}}}
sub Pop       {pop @{$_[0]->{-ptr}}}
sub Push      {push @{$_[0]->{-ptr}}, @_[1 .. $#_]}
sub Shift     {shift @{$_[0]->{-ptr}}}
sub Splice    {
    my $n = scalar @_;		# splice() is wierd!
    return splice @{$_[0]->{-ptr}}, $_[1]                      if $n == 2;
    return splice @{$_[0]->{-ptr}}, $_[1], $_[2]               if $n == 3;
    return splice @{$_[0]->{-ptr}}, $_[1], $_[2], @_[3 .. $#_] if $n >= 4;
}
sub Store     {$_[0]->{-ptr}->[$_[1]] = $_[2]}
sub Storesize {$#{$_[0]->{-ptr}} = $_[1] - 1}
sub Unshift   {unshift @{$_[0]->{-ptr}}, @_[1 .. $#_]}

# Array access methods.

sub CLEAR     {$_[0]->callback('-clear')}
sub DELETE    {$_[0]->callback('-delete', $_[1])}
sub DESTROY   {$_[0]->callback('-destroy')}
sub EXISTS    {$_[0]->callback('-exists', $_[1])}
sub EXTEND    {$_[0]->callback('-extend', $_[1])}
sub FETCH     {$_[0]->callback('-fetch', $_[1])}
sub FETCHSIZE {$_[0]->callback('-fetchsize')}
sub POP       {$_[0]->callback('-pop')}
sub PUSH      {$_[0]->callback('-push', @_[1 .. $#_])}
sub SHIFT     {$_[0]->callback('-shift')}
sub SPLICE    {$_[0]->callback('-splice', @_[1 .. $#_])}
sub STORE     {$_[0]->callback('-store', $_[1], $_[2])}
sub STORESIZE {$_[0]->callback('-storesize', $_[1])}
sub UNSHIFT   {$_[0]->callback('-unshift', @_[1 .. $#_])}

###############################################################################

package Tie::Watch::Hash;

use Carp;
@Tie::Watch::Hash::ISA = qw/Tie::Watch/;

sub TIEHASH {

    my($class, %args) = @_;
    my($variable, $shadow) = @args{-variable, -shadow};
    my %copy = %$variable if $shadow; # make a private copy of user's hash
    $args{-ptr} = $shadow ? \%copy : {};
    my $watch_obj = Tie::Watch->base_watch(%args);
    print "WatchHash new: $variable created, \@_=", join(',', @_), "!\n"
	if $watch_obj->{-debug};
    bless $watch_obj, $class;

} # end TIEHASH

sub Info {$_[0]->SUPER::Info('-ptr', @Tie::Watch::hash_callbacks)}

# Default hash callbacks.

sub Clear    {$_[0]->{-ptr} = ()}
sub Delete   {delete $_[0]->{-ptr}->{$_[1]}}
sub Destroy  {undef %{$_[0]}}
sub Exists   {exists $_[0]->{-ptr}->{$_[1]}}
sub Fetch    {$_[0]->{-ptr}->{$_[1]}}
sub Firstkey {my $c = keys %{$_[0]->{-ptr}}; each %{$_[0]->{-ptr}}}
sub Nextkey  {each %{$_[0]->{-ptr}}}
sub Store    {$_[0]->{-ptr}->{$_[1]} = $_[2]}

# Hash access methods.

sub CLEAR    {$_[0]->callback('-clear')}
sub DELETE   {$_[0]->callback('-delete', $_[1])}
sub DESTROY  {$_[0]->callback('-destroy')}
sub EXISTS   {$_[0]->callback('-exists', $_[1])}
sub FETCH    {$_[0]->callback('-fetch', $_[1])}
sub FIRSTKEY {$_[0]->callback('-firstkey')}
sub NEXTKEY  {$_[0]->callback('-nextkey')}
sub STORE    {$_[0]->callback('-store', $_[1], $_[2])}

1;