use strict;
use warnings;
-use Carp qw/croak/;
-
=head1 NAME
Variable::Magic - Associate user-defined magic to variables from Perl.
=head1 VERSION
-Version 0.30
+Version 0.46
=cut
our $VERSION;
BEGIN {
- $VERSION = '0.30';
+ $VERSION = '0.46';
}
=head1 SYNOPSIS
- use Variable::Magic qw/wizard cast dispell/;
-
- 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)
+ use Variable::Magic qw<wizard cast VMG_OP_INFO_NAME>;
+
+ { # 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" (there is no 'banana' key in %h)
+ $h{pear} = 1; # "key pear stored in helem"
+ }
=head1 DESCRIPTION
-Magic is Perl way of enhancing objects.
-This mechanism lets the user add extra data to any variable and hook syntaxical operations (such as access, assignment or destruction) that can be applied to it.
+Magic is Perl's way of enhancing variables.
+This mechanism lets the user add extra data to any variable and hook syntactical operations (such as access, assignment or destruction) that can be applied to it.
With this module, you can add your own magic to any variable without having to write a single line of XS.
You'll realize that these magic variables look a lot like tied variables.
-It's not surprising, as tied variables are implemented as a special kind of magic, just like any 'irregular' Perl variable : scalars like C<$!>, C<$(> or C<$^W>, the C<%ENV> and C<%SIG> hashes, the C<@ISA> array, C<vec()> and C<substr()> lvalues, L<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 get triggered before the original action takes place, and can't prevent it from happening.
+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 *
=back
-The following actions only apply to hashes and are available iff C<VMG_UVAR> is true.
+The following actions only apply to hashes and are available iff L</VMG_UVAR> is true.
They are referred to as C<uvar> magics.
=over 4
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 FUNCTIONS
=cut
=head2 C<wizard>
- wizard sig => ...,
- data => sub { ... },
- 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 => $bool,
- op_info => [ 0 | VMG_OP_INFO_NAME | VMG_OP_INFO_OBJECT ]
+ wizard(
+ data => sub { ... },
+ get => sub { my ($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 => $bool,
+ op_info => [ 0 | VMG_OP_INFO_NAME | VMG_OP_INFO_OBJECT ],
+ )
This function creates a 'wizard', an opaque type that holds the magic information.
It takes a list of keys / values as argument, whose keys can be :
=item *
-C<sig>
-
-The numerical signature.
-If not specified or undefined, a random signature is generated.
-If the signature matches an already defined magic, then the existant magic object is returned.
-
-=item *
-
C<data>
-A code reference to a private data constructor.
+A code (or string) reference to a private data constructor.
It is called each time this magic is cast on a variable, and the scalar returned is used as private data storage for it.
C<$_[0]> is a reference to the magic object and C<@_[1 .. @_-1]> are all extra arguments that were passed to L</cast>.
C<get>, C<set>, C<len>, C<clear>, C<free>, C<copy>, C<local>, C<fetch>, C<store>, C<exists> and C<delete>
-Code references to the corresponding magic callbacks.
+Code (or string) 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).
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.
=back
+Each callback can be specified as a code or a string reference, in which case the function denoted by the string will be used as the callback.
+
+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.
+
+Here's a simple usage example :
+
# A simple scalar tracer
- my $wiz = wizard get => sub { print STDERR "got ${$_[0]}\n" },
- set => sub { print STDERR "set to ${$_[0]}\n" },
- free => sub { print STDERR "${$_[0]} was deleted\n" }
+ my $wiz = wizard(
+ get => sub { print STDERR "got ${$_[0]}\n" },
+ set => sub { print STDERR "set to ${$_[0]}\n" },
+ free => sub { print STDERR "${$_[0]} was deleted\n" },
+ );
=cut
sub wizard {
- croak 'Wrong number of arguments for wizard()' if @_ % 2;
- my %opts = @_;
- 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;
- push @keys, qw/fetch store exists delete copy_key/ if VMG_UVAR;
- my $ret = eval { _wizard(map $opts{$_}, @keys) };
- if (my $err = $@) {
- $err =~ s/\sat\s+.*?\n//;
- croak $err;
+ if (@_ % 2) {
+ require Carp;
+ Carp::croak('Wrong number of arguments for wizard()');
}
- return $ret;
-}
-
-=head2 C<gensig>
-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.
-
- # Generate a signature
- my $sig = gensig;
-
-=head2 C<getsig>
+ my %opts = @_;
- getsig $wiz
+ my @keys = qw<op_info data get set len clear free copy dup>;
+ push @keys, 'local' if MGf_LOCAL;
+ push @keys, qw<fetch store exists delete copy_key> if VMG_UVAR;
-This accessor returns the magic signature of this wizard.
+ my ($wiz, $err);
+ {
+ local $@;
+ $wiz = eval { _wizard(map $opts{$_}, @keys) };
+ $err = $@;
+ }
+ if ($err) {
+ $err =~ s/\sat\s+.*?\n//;
+ require Carp;
+ Carp::croak($err);
+ }
- # Get $wiz signature
- my $sig = getsig $wiz;
+ return $wiz;
+}
=head2 C<cast>
- cast [$@%&*]var, [$wiz|$sig], ...
+ cast [$@%&*]var, $wiz, ...
This function associates C<$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.
+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, $wiz, 1;
The C<var> argument can be an array or hash value.
Magic for those behaves like for any other scalar, except that it is dispelled when the entry is deleted from the container.
=head2 C<getdata>
- getdata [$@%&*]var, [$wiz|$sig]
+ getdata [$@%&*]var, $wiz
-This accessor fetches the private data associated with the magic C<$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.
+This accessor fetches the private data associated with the magic C<$wiz> in the variable.
+It croaks when C<$wiz> 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, $wiz;
=head2 C<dispell>
- dispell [$@%&*]variable, [$wiz|$sig]
+ dispell [$@%&*]variable, $wiz
The exact opposite of L</cast> : it dissociates C<$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> could be found in the variable, and croaks if the supplied wizard 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
-=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<VMG_UVAR>
When this constant is true, you can use the C<fetch,store,exists,delete> callbacks on hashes.
+Initial VMG_UVAR capability was introduced in perl 5.9.5, with a fully functional implementation
+shipped with perl 5.10.0.
=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.
+Starting from perl 5.11.0, this only refers to pushes in non-void context and hence is false.
+
+=head2 C<VMG_COMPAT_ARRAY_PUSH_NOLEN_VOID>
+
+True for perls that don't call 'len' magic when you push in void context an element in a magical array.
=head2 C<VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID>
True for perls that don't call 'len' magic when taking the C<length> of a magical scalar.
+=head2 C<VMG_COMPAT_GLOB_GET>
+
+True for perls that call 'get' magic for operations on globs.
+
=head2 C<VMG_PERL_PATCHLEVEL>
The perl patchlevel this module was built with, or C<0> for non-debugging perls.
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.
Value to pass with C<op_info> to get a C<B::OP> object representing the current op in the magic callbacks.
+=head1 COOKBOOK
+
+=head2 Associate an object to any perl variable
+
+This technique can be useful for passing user data through limited APIs.
+It is similar to using inside-out objects, but without the drawback of having to implement a complex destructor.
+
+ {
+ package Magical::UserData;
+
+ use Variable::Magic qw<wizard cast getdata>;
+
+ my $wiz = wizard data => sub { \$_[1] };
+
+ sub ud (\[$@%*&]) : lvalue {
+ my ($var) = @_;
+ my $data = &getdata($var, $wiz);
+ unless (defined $data) {
+ $data = \(my $slot);
+ &cast($var, $wiz, $slot)
+ or die "Couldn't cast UserData magic onto the variable";
+ }
+ $$data;
+ }
+ }
+
+ {
+ BEGIN { *ud = \&Magical::UserData::ud }
+
+ my $cb;
+ $cb = sub { print 'Hello, ', ud(&$cb), "!\n" };
+
+ ud(&$cb) = 'world';
+ $cb->(); # Hello, world!
+ }
+
+=head2 Recursively cast magic on datastructures
+
+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>.
+
=head1 PERL MAGIC HISTORY
The places where magic is invoked have changed a bit through perl history.
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>.
+I<g9cdcb38b> : 'len' magic is called again when pushing into a magical array in non-void context.
+
=back
=head1 EXPORT
-The functions L</wizard>, L</gensig>, L</getsig>, L</cast>, L</getdata> and L</dispell> are only exported on request.
+The functions L</wizard>, 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
-use base qw/Exporter/;
+use base qw<Exporter>;
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 VMG_COMPAT_SCALAR_LENGTH_NOLEN/,
- qw/VMG_PERL_PATCHLEVEL/,
- qw/VMG_THREADSAFE/,
- qw/VMG_OP_INFO_NAME VMG_OP_INFO_OBJECT/
- ]
+ 'funcs' => [ qw<wizard cast getdata dispell> ],
+ 'consts' => [ qw<
+ MGf_COPY MGf_DUP MGf_LOCAL VMG_UVAR
+ VMG_COMPAT_ARRAY_PUSH_NOLEN VMG_COMPAT_ARRAY_PUSH_NOLEN_VOID
+ VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID
+ VMG_COMPAT_ARRAY_UNDEF_CLEAR
+ VMG_COMPAT_SCALAR_LENGTH_NOLEN
+ VMG_COMPAT_GLOB_GET
+ VMG_PERL_PATCHLEVEL
+ VMG_THREADSAFE VMG_FORKSAFE
+ VMG_OP_INFO_NAME VMG_OP_INFO_OBJECT
+ > ],
);
our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
$EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
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.
+In order to define magic on hash members, you need at least L<perl> 5.10.0 (see L</VMG_UVAR>)
+
=head1 DEPENDENCIES
L<perl> 5.8.
+A C compiler.
+This module may happen to build with a C++ compiler as well, but don't rely on it, as no guarantee is made in this regard.
+
L<Carp> (standard since perl 5), L<XSLoader> (standard since perl 5.006).
Copy tests need L<Tie::Array> (standard since perl 5.005) and L<Tie::Hash> (since 5.002).
=head1 COPYRIGHT & LICENSE
-Copyright 2007-2009 Vincent Pit, all rights reserved.
+Copyright 2007,2008,2009,2010,2011 Vincent Pit, all rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
projects / perl / modules / Variable-Magic.git / blobdiff