package Variable::Magic;
-use 5.007003;
+use 5.008;
use strict;
use warnings;
=head1 VERSION
-Version 0.28
+Version 0.32
=cut
our $VERSION;
BEGIN {
- $VERSION = '0.28';
+ $VERSION = '0.32';
}
=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
+ $h{pear} = 1; # "key pear stored in helem"
+ }
=head1 DESCRIPTION
Magic is Perl way of enhancing objects.
-This mechanism let the user add extra data to any variable and hook syntaxical operations (such as access, assignation or destruction) that can be applied to it.
-With this module, you can add your own magic to any variable without the pain of the C API.
+This mechanism lets the user add extra data to any variable and hook syntaxical operations (such as access, assignment or destruction) that can be applied to it.
+With this module, you can add your own magic to any variable without having to write a single line of XS.
+
+You'll realize that these magic variables look a lot like tied variables.
+It's not surprising, as tied variables are implemented as a special kind of magic, just like any 'irregular' Perl variable : scalars like C<$!>, 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.
-Magic differs from tieing and overloading in several ways :
+Still, the magic made available by this module differs from tieing and overloading in several ways :
=over 4
=item *
-Magic isn't copied on assignation (as for blessed references) : you attach it to variables, not values.
+It isn't copied on assignment.
+
+You attach it to variables, not values (as for blessed references).
=item *
-It doesn't replace the original semantics : magic callbacks trigger before the original action take place, and can't prevent it to happen.
+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.
=item *
-It's mostly invisible at the Perl level : magical and non-magical variables cannot be distinguished with C<ref>, C<reftype> or another trick.
+It's type-agnostic.
+
+The same magic can be applied on scalars, arrays, hashes, subs or globs.
+But the same hook (see below for a list) may trigger differently depending on the the type of the variable.
=item *
-It's notably faster, since perl's way of handling magic is lighter by nature, and there's no need for any method resolution.
+It's mostly invisible at the Perl level.
+
+Magical and non-magical variables cannot be distinguished with C<ref>, C<tied> or another trick.
+
+=item *
+
+It's notably faster.
+
+Mainly because perl's way of handling magic is lighter by nature, and because there's no need for any method resolution.
+Also, since you don't have to reimplement all the variable semantics, you only pay for what you actually use.
=back
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 *
C<clear>
-This magic is invoked when the variable is reset, such as when an array is emptied.
+This magic is invoked when a container variable is reset, i.e. when an array or a hash 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>).
=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).
-
-=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.
+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
wizard sig => ...,
data => sub { ... },
- get => sub { my ($ref, $data) = @_; ... },
- set => sub { my ($ref, $data) = @_; ... },
- len => sub { my ($ref, $data, $len) = @_; ... ; return $newlen; },
- clear => sub { my ($ref, $data) = @_; ... },
- free => sub { my ($ref, $data) = @_, ... },
- copy => sub { my ($ref, $data, $key, $elt) = @_; ... },
- local => sub { my ($ref, $data) = @_; ... },
- fetch => sub { my ($ref, $data, $key) = @_; ... },
- store => sub { my ($ref, $data, $key) = @_; ... },
- exists => sub { my ($ref, $data, $key) = @_; ... },
- delete => sub { my ($ref, $data, $key) = @_; ... },
- copy_key => $bool
+ get => sub { my ($ref, $data [, $op]) = @_; ... },
+ set => sub { my ($ref, $data [, $op]) = @_; ... },
+ len => sub { my ($ref, $data, $len [, $op]) = @_; ... ; return $newlen; },
+ clear => sub { my ($ref, $data [, $op]) = @_; ... },
+ free => sub { my ($ref, $data [, $op]) = @_, ... },
+ copy => sub { my ($ref, $data, $key, $elt [, $op]) = @_; ... },
+ local => sub { my ($ref, $data [, $op]) = @_; ... },
+ fetch => sub { my ($ref, $data, $key [, $op]) = @_; ... },
+ store => sub { my ($ref, $data, $key [, $op]) = @_; ... },
+ exists => sub { my ($ref, $data, $key [, $op]) = @_; ... },
+ delete => sub { my ($ref, $data, $key [, $op]) = @_; ... },
+ copy_key => $bool,
+ op_info => [ 0 | VMG_OP_INFO_NAME | VMG_OP_INFO_OBJECT ]
This function creates a 'wizard', an opaque type that holds the magic information.
It takes a list of keys / values as argument, whose keys can be :
Code references to the corresponding magic callbacks.
You don't have to specify all of them : the magic associated with undefined entries simply won't be hooked.
In those callbacks, C<$_[0]> is always a reference to the magic object and C<$_[1]> is always the private data (or C<undef> when no private data constructor was supplied).
+
+Moreover, when you pass C<< op_info => $num >> to C<wizard>, the last element of C<@_> will be the current op name if C<$num == VMG_OP_INFO_NAME> and a C<B::OP> object representing the current op if C<$num == VMG_OP_INFO_OBJECT>.
+Both have a performance hit, but just getting the name is lighter than getting the op object.
+
Other arguments are specific to the magic hooked :
=over 8
C<len>
-When the variable is an array, C<$_[2]> contains the normal length.
-The callback is also expected to return the new scalar or array length.
+When the variable is an array or a scalar, C<$_[2]> contains the non-magical length.
+The callback can return the new scalar or array length to use, or C<undef> to default to the normal length.
=item *
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 {
croak 'Wrong number of arguments for wizard()' if @_ % 2;
my %opts = @_;
- my @keys = qw/sig data get set len clear free/;
+ my @keys = qw/sig data op_info get set len clear free/;
push @keys, 'copy' if MGf_COPY;
push @keys, 'dup' if MGf_DUP;
push @keys, 'local' if MGf_LOCAL;
my $x;
die 'error' unless cast $x, $wiz;
+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.
+For example, if you want to call C<POSIX::tzset> each time the C<'TZ'> environment variable is changed in C<%ENV>, you can use :
+
+ use POSIX;
+ cast $ENV{TZ}, wizard set => sub { POSIX::tzset(); () };
+
+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
our @EXPORT = ();
our %EXPORT_TAGS = (
'funcs' => [ qw/wizard gensig getsig cast getdata dispell/ ],
- 'consts' => [ 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/,
- qw/VMG_COMPAT_SCALAR_LENGTH_NOLEN/,
+ 'consts' => [
+ 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/,
+ qw/VMG_OP_INFO_NAME VMG_OP_INFO_OBJECT/
+ ]
);
our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
$EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
=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.
=head1 DEPENDENCIES
-L<perl> 5.7.3.
+L<perl> 5.8.
L<Carp> (standard since perl 5), L<XSLoader> (standard since perl 5.006).
projects / perl / modules / Variable-Magic.git / blobdiff