1 package Variable::Magic;
10 Variable::Magic - Associate user-defined magic to variables from Perl.
18 our $VERSION = '0.02';
22 use Variable::Magic qw/wizard cast dispell/;
24 my $wiz = wizard set => sub { print STDERR "now set to $_[0]!\n" };
27 $a = 2; # "now set to 2!"
33 Magic is Perl way of enhancing objects. This mechanism let the user add extra data to any variable and overload syntaxical operations (such as access, assignation or destruction) that can be applied to it. With this module, you can add your own magic to any variable without the pain of the C API.
35 The operations that can be overloaded are :
41 This magic is invoked when the variable is evaluated (does not include array/hash subscripts and slices).
45 This one is triggered each time the value of the variable changes (includes array/hash subscripts and slices).
49 This magic is a little special : it is called when the 'size' or the 'length' of the variable has to be known by Perl. Typically, it's the magic involved when an array is evaluated in scalar context, but also on array assignation and loops (C<for>, C<map> or C<grep>). The callback has then to return the length as an integer.
53 This magic is invoked when the variable is reset, such as when an array is emptied. Please note that this is different from undefining the variable, even though the magic is called when the clearing is a result of the undefine (e.g. for an array, but actually a bug prevent it to work before perl 5.9.5 - see the L<history|/PERL MAGIC HISTORY>).
57 This last one can be considered as an object destructor. It happens when the variable goes out of scope (with the exception of global scope), but not when it is undefined.
61 To prevent any clash between different magics defined with this module, an unique numerical signature is attached to each kind of magic (i.e. each set of callbacks for magic operations).
63 =head1 PERL MAGIC HISTORY
69 =item 'len' magic is no longer called when pushing an element into a magic array.
77 =item 'clear' magic wasn't invoked when undefining an array. The bug is fixed as of this version.
85 The minimum integer used as a signature for user-defined magic.
89 use constant SIG_MIN => 2 ** 8;
93 The maximum integer used as a signature for user-defined magic.
97 use constant SIG_MAX => 2 ** 16 - 1;
101 SIG_NBR = SIG_MAX - SIG_MIN + 1
105 use constant SIG_NBR => SIG_MAX - SIG_MIN + 1;
113 XSLoader::load(__PACKAGE__, $VERSION);
119 wizard sig => .., data => ..., get => .., set => .., len => .., clear => .., free => ..
121 This function creates a 'wizard', an opaque type that holds the magic information. It takes a list of keys / values as argument, whose keys can be :
127 The numerical signature. If not specified or undefined, a random signature is generated.
131 A code reference to a private data constructor. It will be called each time this magic is cast on a variable, and the scalar returned will be used as private data storage for it.
133 =item C<'get'>, C<'set'>, C<'len'>, C<'clear'> and C<'free'>
135 Code references to corresponding magic callbacks. You don't have to specify all of them : the magic associated with undefined entries simply won't be hooked. When the magic variable is an array or a hash, C<$_[0]> is a reference to it, but directly references it otherwise. C<$_[1]> is the private data (or C<undef> when no private data constructor was supplied). In the special case of C<len> magic and when the variable is an array, C<$_[2]> contains its normal length.
139 # A simple scalar tracer
140 my $wiz = wizard get => sub { print STDERR "got $_[0]\n" },
141 set => sub { print STDERR "set to $_[0]\n" },
142 free => sub { print STDERR "$_[0] was deleted\n" }
147 croak 'Wrong number of arguments for wizard()' if @_ % 2;
150 if (defined $opts{sig}) {
151 $sig = int $opts{sig};
152 $sig += SIG_MIN if $sig < SIG_MIN;
153 $sig %= SIG_MAX + 1 if $sig > SIG_MAX;
157 return _wizard($sig, map { $opts{$_} } qw/get set len clear free data/);
162 With this tool, you can manually generate random magic signature between SIG_MIN and SIG_MAX inclusive. That's the way L</wizard> creates them when no signature is supplied.
164 # Generate a signature
171 my $used = ~~keys %wizz;
172 croak 'Too many magic signatures used' if $used == SIG_NBR;
173 do { $sig = SIG_MIN + int(rand(SIG_NBR)) } while $wizz{$sig};
181 This accessor returns the magic signature of this wizard.
184 my $sig = getsig $wiz;
188 cast [$@%&*]var, $wiz
190 This function associates C<$wiz> magic to the variable supplied, without overwriting any other kind of magic. It returns true on success or when C<$wiz> magic is already present, and false on error.
194 die 'error' unless cast $x, $wiz;
198 getdata [$@%&*]var, $wiz
200 This accessor fetches the private data associated with the magic C<$wiz> in the variable. C<undef> is returned when no such magic or data is found.
204 dispell [$@%&*]variable, $wiz
205 dispell [$@%&*]variable, $sig
207 The exact opposite of L</cast> : it dissociates C<$wiz> magic from the variable. You can also pass the magic signature as the second argument. True is returned on success, and false on error or when no magic represented by C<$wiz> could be found in the variable.
210 die 'no such magic or error' unless dispell $x, $wiz;
214 The functions L</wizard>, L</gensig>, L</getsig>, L</cast>, L</getdata> and L</dispell> are only exported on request. All of them are exported by the tags C<':funcs'> and C<':all'>.
216 The constants L</SIG_MIN>, L</SIG_MAX> and L</SIG_NBR> are also only exported on request. They are all exported by the tags C<':consts'> and C<':all'>.
220 use base qw/Exporter/;
224 'funcs' => [ qw/wizard gensig getsig cast getdata dispell/ ],
225 'consts' => [ qw/SIG_MIN SIG_MAX SIG_NBR/ ]
227 our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
228 $EXPORT_TAGS{'all'} = \@EXPORT_OK;
232 L<Carp> (standard since perl 5), L<XSLoader> (standard since perl 5.006).
234 Tests use L<Symbol> (standard since perl 5.002).
238 L<perlguts> and L<perlapi> for internal information about magic.
242 Vincent Pit, C<< <perl at profvince.com> >>
246 Please report any bugs or feature requests to
247 C<bug-variable-magic at rt.cpan.org>, or through the web interface at
248 L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Variable-Magic>.
249 I will be notified, and then you'll automatically be notified of progress on
250 your bug as I make changes.
254 You can find documentation for this module with the perldoc command.
256 perldoc Variable::Magic
258 =head1 COPYRIGHT & LICENSE
260 Copyright 2007 Vincent Pit, all rights reserved.
262 This program is free software; you can redistribute it and/or modify it
263 under the same terms as Perl itself.
267 1; # End of Variable::Magic