=head1 VERSION
-Version 0.30
+Version 0.36
=cut
our $VERSION;
BEGIN {
- $VERSION = '0.30';
+ $VERSION = '0.36';
}
=head1 SYNOPSIS
- use Variable::Magic qw/wizard cast dispell/;
+ use Variable::Magic qw/wizard cast VMG_OP_INFO_NAME/;
- my $wiz = wizard set => sub { print STDERR "now set to ${$_[0]}!\n" };
- my $a = 1;
- cast $a, $wiz;
- $a = 2; # "now set to 2!"
- dispell $a, $wiz;
- $a = 3 # (nothing)
+ { # A variable tracer
+ my $wiz = wizard set => sub { print "now set to ${$_[0]}!\n" },
+ free => sub { print "destroyed!\n" };
+
+ my $a = 1;
+ cast $a, $wiz;
+ $a = 2; # "now set to 2!"
+ } # "destroyed!"
+
+ { # A hash with a default value
+ my $wiz = wizard data => sub { $_[1] },
+ fetch => sub { $_[2] = $_[1] unless exists $_[0]->{$_[2]}; () },
+ store => sub { print "key $_[2] stored in $_[-1]\n" },
+ copy_key => 1,
+ op_info => VMG_OP_INFO_NAME;
+
+ my %h = (_default => 0, apple => 2);
+ cast %h, $wiz, '_default';
+ print $h{banana}, "\n"; # "0", because the 'banana' key doesn't exist in %h
+ $h{pear} = 1; # "key pear stored in helem"
+ }
=head1 DESCRIPTION
With this module, you can add your own magic to any variable without having to write a single line of XS.
You'll realize that these magic variables look a lot like tied variables.
-It's not surprising, as tied variables are implemented as a special kind of magic, just like any 'irregular' Perl variable : scalars like C<$!>, C<$(> or C<$^W>, the C<%ENV> and C<%SIG> hashes, the C<@ISA> array, C<vec()> and C<substr()> lvalues, L<thread::shared> variables...
+It's not surprising, as tied variables are implemented as a special kind of magic, just like any 'irregular' Perl variable : scalars like C<$!>, C<$(> or C<$^W>, the C<%ENV> and C<%SIG> hashes, the C<@ISA> array, C<vec()> and C<substr()> lvalues, L<threads::shared> variables...
They all share the same underlying C API, and this module gives you direct access to it.
Still, the magic made available by this module differs from tieing and overloading in several ways :
It doesn't replace the original semantics.
-Magic callbacks trigger before the original action take place, and can't prevent it to happen.
-This makes catching individual events easier than with C<tie>, where you have to provide fallbacks methods for all actions by usually inheriting from the correct C<Tie::Std*> class and overriding individual methods in your own class.
+Magic callbacks usually trigger before the original action take place, and can't prevent it to happen.
+This also makes catching individual events easier than with C<tie>, where you have to provide fallbacks methods for all actions by usually inheriting from the correct C<Tie::Std*> class and overriding individual methods in your own class.
=item *
C<get>
-This magic is invoked when the variable is evaluated (does not include array/hash subscripts and slices).
+This magic is invoked when the variable is evaluated.
+It is never called for arrays and hashes.
=item *
C<set>
-This one is triggered each time the value of the variable changes (includes array/hash subscripts and slices).
+This one is triggered each time the value of the variable changes.
+It is called for array subscripts and slices, but never for hashes.
=item *
C<free>
This 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.
+It happens when the variable goes out of scope, but not when it is undefined.
=item *
You can refer to the tests to have more insight of where the different magics are invoked.
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).
+At the C level, magic tokens owned by magic created by this module have their C<< mg->mg_private >> field set to C<0x3891> or C<0x3892>, so please don't use these magic (sic) numbers in other extensions.
=head1 FUNCTIONS
C<$_[2]> is an alias to the current key.
Nothing prevents you from changing it, but be aware that there lurk dangerous side effects.
-For example, it may righteously be readonly if the key was a bareword.
+For example, it may rightfully be readonly if the key was a bareword.
You can get a copy instead by passing C<< copy_key => 1 >> to L</wizard>, which allows you to safely assign to C<$_[2]> in order to e.g. redirect the action to another key.
This however has a little performance drawback because of the copy.
set => sub { print STDERR "set to ${$_[0]}\n" },
free => sub { print STDERR "${$_[0]} was deleted\n" }
+Note that C<free> callbacks are I<never> called during global destruction, as there's no way to ensure that the wizard and the C<free> callback weren't destroyed before the variable.
+
=cut
sub wizard {
This function associates C<$wiz> magic to the variable supplied, without overwriting any other kind of magic.
You can also supply the numeric signature C<$sig> instead of C<$wiz>.
-It returns true on success or when C<$wiz> magic is already present, C<0> on error, and C<undef> when no magic corresponds to the given signature (in case C<$sig> was supplied).
-All extra arguments specified after C<$wiz> are passed to the private data constructor.
+It returns true on success or when C<$wiz> magic is already present, and croaks on error or when no magic corresponds to the given signature (in case a C<$sig> was supplied).
+All extra arguments specified after C<$wiz> are passed to the private data constructor in C<@_[1 .. @_-1]>.
If the variable isn't a hash, any C<uvar> callback of the wizard is safely ignored.
- # Casts $wiz onto $x. If $wiz isn't a signature, undef can't be returned.
+ # Casts $wiz onto $x, and pass '1' to the data constructor.
my $x;
- die 'error' unless cast $x, $wiz;
+ cast $x, $wiz, 1;
The C<var> argument can be an array or hash value.
Magic for those behaves like for any other scalar, except that it is dispelled when the entry is deleted from the container.
If you want to overcome the possible deletion of the C<'TZ'> entry, you have no choice but to rely on C<store> uvar magic.
+C<cast> can be called from any magical callback, and in particular from C<data>.
+This allows you to recursively cast magic on datastructures :
+
+ my $wiz;
+ $wiz = wizard
+ data => sub {
+ my ($var, $depth) = @_;
+ $depth ||= 0;
+ my $r = ref $var;
+ if ($r eq 'ARRAY') {
+ &cast((ref() ? $_ : \$_), $wiz, $depth + 1) for @$var;
+ } elsif ($r eq 'HASH') {
+ &cast((ref() ? $_ : \$_), $wiz, $depth + 1) for values %$var;
+ }
+ return $depth;
+ },
+ free => sub {
+ my ($var, $depth) = @_;
+ my $r = ref $var;
+ print "free $r at depth $depth\n";
+ ();
+ };
+
+ {
+ my %h = (
+ a => [ 1, 2 ],
+ b => { c => 3 }
+ );
+ cast %h, $wiz;
+ }
+
+When C<%h> goes out of scope, this will print something among the lines of :
+
+ free HASH at depth 0
+ free HASH at depth 1
+ free SCALAR at depth 2
+ free ARRAY at depth 1
+ free SCALAR at depth 3
+ free SCALAR at depth 3
+
+Of course, this example does nothing with the values that are added after the C<cast>.
+
=head2 C<getdata>
getdata [$@%&*]var, [$wiz|$sig]
This accessor fetches the private data associated with the magic C<$wiz> (or the signature C<$sig>) in the variable.
-C<undef> is returned when no such magic or data is found, or when C<$sig> does not represent a current valid magic object.
+It croaks when C<$wiz> or C<$sig> do not represent a valid magic object, and returns an empty list if no such magic is attached to the variable or when the wizard has no data constructor.
- # Get the attached data.
- my $data = getdata $x, $wiz or die 'no such magic or magic has no data';
+ # Get the attached data, or undef if the wizard does not attach any.
+ my $data = getdata $x, $wiz;
=head2 C<dispell>
The exact opposite of L</cast> : it dissociates C<$wiz> magic from the variable.
You can also pass the magic signature C<$sig> as the second argument.
-True is returned on success, C<0> on error or when no magic represented by C<$wiz> could be found in the variable, and C<undef> when no magic corresponds to the given signature (in case C<$sig> was supplied).
+This function returns true on success, C<0> when no magic represented by C<$wiz> or C<$sig> could be found in the variable, and croaks if the supplied wizard or signature is invalid.
- # Dispell now. If $wiz isn't a signature, undef can't be returned.
- die 'no such magic or error' unless dispell $x, $wiz;
+ # Dispell now.
+ die 'no such magic in $x' unless dispell $x, $wiz;
=head1 CONSTANTS
True iff this module could have been built with thread-safety features enabled.
+=head2 C<VMG_FORKSAFE>
+
+True iff this module could have been built with fork-safety features enabled.
+This will always be true except on Windows where it's false for perl 5.10.0 and below .
+
=head2 C<VMG_OP_INFO_NAME>
Value to pass with C<op_info> to get the current op name in the magic callbacks.
qw/SIG_MIN SIG_MAX SIG_NBR MGf_COPY MGf_DUP MGf_LOCAL VMG_UVAR/,
qw/VMG_COMPAT_ARRAY_PUSH_NOLEN VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID VMG_COMPAT_ARRAY_UNDEF_CLEAR VMG_COMPAT_SCALAR_LENGTH_NOLEN/,
qw/VMG_PERL_PATCHLEVEL/,
- qw/VMG_THREADSAFE/,
+ qw/VMG_THREADSAFE VMG_FORKSAFE/,
qw/VMG_OP_INFO_NAME VMG_OP_INFO_OBJECT/
]
);
projects / perl / modules / Variable-Magic.git / blobdiff