=head1 VERSION
-Version 0.30
+Version 0.31
=cut
our $VERSION;
BEGIN {
- $VERSION = '0.30';
+ $VERSION = '0.31';
}
=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
Magic is Perl way of enhancing objects.
-This mechanism lets the user add extra data to any variable and hook syntaxical operations (such as access, assignation or destruction) that can be applied to it.
+This mechanism lets the user add extra data to any variable and hook syntaxical operations (such as access, assignment or destruction) that can be applied to it.
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.
=item *
-It isn't copied on assignation.
+It isn't copied on assignment.
You attach it to variables, not values (as for blessed references).
C<len>
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>).
+Typically, it's the magic involved when an array is evaluated in scalar context, but also on array assignment and loops (C<for>, C<map> or C<grep>).
The callback has then to return the length as an integer.
=item *
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).
-=head1 PERL MAGIC HISTORY
-
-The places where magic is invoked have changed a bit through perl history.
-Here's a little list of the most recent ones.
-
-=over 4
-
-=item *
-
-B<5.6.x>
-
-I<p14416> : 'copy' and 'dup' magic.
-
-=item *
-
-B<5.8.9>
-
-I<p28160> : Integration of I<p25854> (see below).
-
-I<p32542> : Integration of I<p31473> (see below).
-
-=item *
-
-B<5.9.3>
-
-I<p25854> : 'len' magic is no longer called when pushing an element into a magic array.
-
-I<p26569> : 'local' magic.
-
-=item *
-
-B<5.9.5>
-
-I<p31064> : Meaningful 'uvar' magic.
-
-I<p31473> : 'clear' magic wasn't invoked when undefining an array.
-The bug is fixed as of this version.
-
-=item *
-
-B<5.10.0>
-
-Since C<PERL_MAGIC_uvar> is uppercased, C<hv_magic_check()> triggers 'copy' magic on hash stores for (non-tied) hashes that also have 'uvar' magic.
-
-=item *
-
-B<5.11.x>
-
-I<p32969> : 'len' magic is no longer invoked when calling C<length> with a magical scalar.
-
-I<p34908> : 'len' magic is no longer called when pushing / unshifting an element into a magical array in void context.
-The C<push> part was already covered by I<p25854>.
-
-=back
-
-=head1 CONSTANTS
-
-=head2 C<SIG_MIN>
-
-The minimum integer used as a signature for user-defined magic.
-
-=head2 C<SIG_MAX>
-
-The maximum integer used as a signature for user-defined magic.
-
-=head2 C<SIG_NBR>
-
- SIG_NBR = SIG_MAX - SIG_MIN + 1
-
-=head2 C<MGf_COPY>
-
-Evaluates to true iff the 'copy' magic is available.
-
-=head2 C<MGf_DUP>
-
-Evaluates to true iff the 'dup' magic is available.
-
-=head2 C<MGf_LOCAL>
-
-Evaluates to true iff the 'local' magic is available.
-
-=head2 C<VMG_UVAR>
-
-When this constant is true, you can use the C<fetch,store,exists,delete> callbacks on hashes.
-
-=head2 C<VMG_COMPAT_ARRAY_PUSH_NOLEN>
-
-True for perls that don't call 'len' magic when you push an element in a magical array.
-
-=head2 C<VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID>
-
-True for perls that don't call 'len' magic when you unshift in void context an element in a magical array.
-
-=head2 C<VMG_COMPAT_ARRAY_UNDEF_CLEAR>
-
-True for perls that call 'clear' magic when undefining magical arrays.
-
-=head2 C<VMG_COMPAT_SCALAR_LENGTH_NOLEN>
-
-True for perls that don't call 'len' magic when taking the C<length> of a magical scalar.
-
-=head2 C<VMG_PERL_PATCHLEVEL>
-
-The perl patchlevel this module was built with, or C<0> for non-debugging perls.
-
-=head2 C<VMG_THREADSAFE>
-
-True iff this module could have been built with thread-safety features enabled.
-
-=head2 C<VMG_OP_INFO_NAME>
-
-Value to pass with C<op_info> to get the current op name in the magic callbacks.
-
-=head2 C<VMG_OP_INFO_OBJECT>
-
-Value to pass with C<op_info> to get a C<B::OP> object representing the current op in the magic callbacks.
-
=head1 FUNCTIONS
=cut
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> coderef weren't destroyed before the scalar.
+
=cut
sub wizard {
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]
# Dispell now. If $wiz isn't a signature, undef can't be returned.
die 'no such magic or error' unless dispell $x, $wiz;
+=head1 CONSTANTS
+
+=head2 C<SIG_MIN>
+
+The minimum integer used as a signature for user-defined magic.
+
+=head2 C<SIG_MAX>
+
+The maximum integer used as a signature for user-defined magic.
+
+=head2 C<SIG_NBR>
+
+ SIG_NBR = SIG_MAX - SIG_MIN + 1
+
+=head2 C<MGf_COPY>
+
+Evaluates to true iff the 'copy' magic is available.
+
+=head2 C<MGf_DUP>
+
+Evaluates to true iff the 'dup' magic is available.
+
+=head2 C<MGf_LOCAL>
+
+Evaluates to true iff the 'local' magic is available.
+
+=head2 C<VMG_UVAR>
+
+When this constant is true, you can use the C<fetch,store,exists,delete> callbacks on hashes.
+
+=head2 C<VMG_COMPAT_ARRAY_PUSH_NOLEN>
+
+True for perls that don't call 'len' magic when you push an element in a magical array.
+
+=head2 C<VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID>
+
+True for perls that don't call 'len' magic when you unshift in void context an element in a magical array.
+
+=head2 C<VMG_COMPAT_ARRAY_UNDEF_CLEAR>
+
+True for perls that call 'clear' magic when undefining magical arrays.
+
+=head2 C<VMG_COMPAT_SCALAR_LENGTH_NOLEN>
+
+True for perls that don't call 'len' magic when taking the C<length> of a magical scalar.
+
+=head2 C<VMG_PERL_PATCHLEVEL>
+
+The perl patchlevel this module was built with, or C<0> for non-debugging perls.
+
+=head2 C<VMG_THREADSAFE>
+
+True iff this module could have been built with thread-safety features enabled.
+
+=head2 C<VMG_OP_INFO_NAME>
+
+Value to pass with C<op_info> to get the current op name in the magic callbacks.
+
+=head2 C<VMG_OP_INFO_OBJECT>
+
+Value to pass with C<op_info> to get a C<B::OP> object representing the current op in the magic callbacks.
+
+=head1 PERL MAGIC HISTORY
+
+The places where magic is invoked have changed a bit through perl history.
+Here's a little list of the most recent ones.
+
+=over 4
+
+=item *
+
+B<5.6.x>
+
+I<p14416> : 'copy' and 'dup' magic.
+
+=item *
+
+B<5.8.9>
+
+I<p28160> : Integration of I<p25854> (see below).
+
+I<p32542> : Integration of I<p31473> (see below).
+
+=item *
+
+B<5.9.3>
+
+I<p25854> : 'len' magic is no longer called when pushing an element into a magic array.
+
+I<p26569> : 'local' magic.
+
+=item *
+
+B<5.9.5>
+
+I<p31064> : Meaningful 'uvar' magic.
+
+I<p31473> : 'clear' magic wasn't invoked when undefining an array.
+The bug is fixed as of this version.
+
+=item *
+
+B<5.10.0>
+
+Since C<PERL_MAGIC_uvar> is uppercased, C<hv_magic_check()> triggers 'copy' magic on hash stores for (non-tied) hashes that also have 'uvar' magic.
+
+=item *
+
+B<5.11.x>
+
+I<p32969> : 'len' magic is no longer invoked when calling C<length> with a magical scalar.
+
+I<p34908> : 'len' magic is no longer called when pushing / unshifting an element into a magical array in void context.
+The C<push> part was already covered by I<p25854>.
+
+=back
+
=head1 EXPORT
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'>.
-The constants L</SIG_MIN>, L</SIG_MAX>, L</SIG_NBR>, L</MGf_COPY>, L</MGf_DUP>, L</MGf_LOCAL> and L</VMG_UVAR> are also only exported on request.
-They are all exported by the tags C<':consts'> and C<':all'>.
+All the constants are also only exported on request, either individually or by the tags C<':consts'> and C<':all'>.
=cut
=head1 CAVEATS
-If you store a magic object in the private data slot, the magic won't be accessible by L</getdata> since it's not copied by assignation.
+If you store a magic object in the private data slot, the magic won't be accessible by L</getdata> since it's not copied by assignment.
The only way to address this would be to return a reference.
If you define a wizard with a C<free> callback and cast it on itself, this destructor won't be called because the wizard will be destroyed first.
projects / perl / modules / Variable-Magic.git / blobdiff