package Variable::Magic;
-use 5.007003;
+use 5.008;
use strict;
use warnings;
-use Carp qw/croak/;
-
=head1 NAME
Variable::Magic - Associate user-defined magic to variables from Perl.
=head1 VERSION
-Version 0.28
+Version 0.52
=cut
our $VERSION;
BEGIN {
- $VERSION = '0.28';
+ $VERSION = '0.52';
}
=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)
+ $h{pear} = 1; # "key pear stored in helem"
+ }
=head1 DESCRIPTION
-Magic is Perl way of enhancing objects.
-This mechanism let the user add extra data to any variable and hook syntaxical operations (such as access, assignation or destruction) that can be applied to it.
-With this module, you can add your own magic to any variable without the pain of the C API.
+Magic is Perl's way of enhancing variables.
+This mechanism lets the user add extra data to any variable and hook syntactical operations (such as access, assignment or destruction) that can be applied to it.
+With this module, you can add your own magic to any variable without having to write a single line of XS.
+
+You'll realize that these magic variables look a lot like tied variables.
+It is not surprising, as tied variables are implemented as a special kind of magic, just like any 'irregular' Perl variable : scalars like C<$!>, 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.
+Magic is not copied on assignment.
+
+You attach it to variables, not values (as for blessed references).
+
+=item *
+
+Magic does not replace the original semantics.
+
+Magic callbacks usually get triggered before the original action takes place, and cannot 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 *
+
+Magic is multivalued.
+
+You can safely apply different kinds of magics to the same variable, and each of them will be invoked successively.
=item *
-It doesn't replace the original semantics : magic callbacks trigger before the original action take place, and can't prevent it to happen.
+Magic is 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 type of the variable.
=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.
+Magic is invisible at Perl level.
+
+Magical and non-magical variables cannot be distinguished with C<ref>, C<tied> or another trick.
=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.
+Magic is notably faster.
+
+Mainly because perl's way of handling magic is lighter by nature, and because there is 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
=item *
-C<get>
+I<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>
+I<set>
-This one is triggered each time the value of the variable changes (includes array/hash subscripts and slices).
+This magic is called each time the value of the variable changes.
+It is called for array subscripts and slices, but never for hashes.
=item *
-C<len>
+I<len>
+
+This magic only applies to arrays (though it used to also apply to scalars), and is triggered when the 'size' or the 'length' of the variable has to be known by Perl.
+This is typically 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 length is returned from the callback as an integer.
-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.
+Starting from perl 5.12, this magic is no longer called by the C<length> keyword, and starting from perl 5.17.4 it is also no longer called for scalars in any situation, making this magic only meaningful on arrays.
+You can use the constants L</VMG_COMPAT_SCALAR_LENGTH_NOLEN> and L</VMG_COMPAT_SCALAR_NOLEN> to see if this magic is available for scalars or not.
=item *
-C<clear>
+I<clear>
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>).
=item *
-C<free>
+I<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.
+This magic is called when a variable is destroyed as the result of going out of scope (but not when it is undefined).
+It behaves roughly like Perl object destructors (i.e. C<DESTROY> methods), except that exceptions thrown from inside a I<free> callback will always be propagated to the surrounding code.
=item *
-C<copy>
+I<copy>
-This magic only applies to tied arrays and hashes.
-It fires when you try to access or change their elements.
-It is available on your perl iff C<MGf_COPY> is true.
+This magic only applies to tied arrays and hashes, and fires when you try to access or change their elements.
=item *
-C<dup>
+I<dup>
-Invoked when the variable is cloned across threads.
-Currently not available.
+This magic is invoked when the variable is cloned across threads.
+It is currently not available.
=item *
-C<local>
+I<local>
When this magic is set on a variable, all subsequent localizations of the variable will trigger the callback.
-It is available on your perl iff C<MGf_LOCAL> is true.
+It is available on your perl if and only if C<MGf_LOCAL> is true.
=back
-The following actions only apply to hashes and are available iff C<VMG_UVAR> is true.
-They are referred to as C<uvar> magics.
+The following actions only apply to hashes and are available if and only if L</VMG_UVAR> is true.
+They are referred to as I<uvar> magics.
=over 4
=item *
-C<fetch>
+I<fetch>
-This magic happens each time an element is fetched from the hash.
+This magic is invoked each time an element is fetched from the hash.
=item *
-C<store>
+I<store>
This one is called when an element is stored into the hash.
=item *
-C<exists>
+I<exists>
This magic fires when a key is tested for existence in the hash.
=item *
-C<delete>
+I<delete>
-This last one triggers when a key is deleted in the hash, regardless of whether the key actually exists in it.
+This magic is triggered when a key is deleted in the hash, regardless of whether the key actually exists in it.
=back
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
-=head1 PERL MAGIC HISTORY
+=cut
-The places where magic is invoked have changed a bit through perl history.
-Here's a little list of the most recent ones.
+BEGIN {
+ require XSLoader;
+ XSLoader::load(__PACKAGE__, $VERSION);
+}
+
+=head2 C<wizard>
+
+ wizard(
+ data => sub { ... },
+ get => sub { my ($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 => $bool,
+ op_info => [ 0 | VMG_OP_INFO_NAME | VMG_OP_INFO_OBJECT ],
+ )
+
+This function creates a 'wizard', an opaque object that holds the magic information.
+It takes a list of keys / values as argument, whose keys can be :
=over 4
=item *
-B<5.6.x>
+C<data>
-I<p14416> : 'copy' and 'dup' magic.
+A code (or string) reference to a private data constructor.
+It is called in scalar context each time the magic is cast onto a variable, with C<$_[0]> being a reference to this variable and C<@_[1 .. @_-1]> being all extra arguments that were passed to L</cast>.
+The scalar returned from this call is then attached to the variable and can be retrieved later with L</getdata>.
=item *
-B<5.8.9>
+C<get>, C<set>, C<len>, C<clear>, C<free>, C<copy>, C<local>, C<fetch>, C<store>, C<exists> and C<delete>
-I<p28160> : Integration of I<p25854> (see below).
+Code (or string) references to the respective magic callbacks.
+You don't have to specify all of them : the magic corresponding to undefined entries will simply not be hooked.
-I<p32542> : Integration of I<p31473> (see below).
+When those callbacks are executed, C<$_[0]> is a reference to the magic variable and C<$_[1]> is the associated private data (or C<undef> when no private data constructor is supplied with the wizard).
+Other arguments depend on which kind of magic is involved :
+
+=over 8
=item *
-B<5.9.3>
+I<len>
+
+C<$_[2]> contains the natural, non-magical length of the variable (which can only be a scalar or an array as I<len> magic is only relevant for these types).
+The callback is expected to return the new scalar or array length to use, or C<undef> to default to the normal length.
-I<p25854> : 'len' magic is no longer called when pushing an element into a magic array.
+=item *
+
+I<copy>
-I<p26569> : 'local' magic.
+C<$_[2]> is a either an alias or a copy of the current key, and C<$_[3]> is an alias to the current element (i.e. the value).
+Because C<$_[2]> might be a copy, it is useless to try to change it or cast magic on it.
=item *
-B<5.9.5>
+I<fetch>, I<store>, I<exists> and I<delete>
-I<p31064> : Meaningful 'uvar' magic.
+C<$_[2]> is an alias to the current key.
+Note that C<$_[2]> may rightfully be readonly if the key comes from a bareword, and as such it is unsafe to assign to it.
+You can ask for a copy instead by passing C<< copy_key => 1 >> to L</wizard> which, at the price of a small performance hit, allows you to safely assign to C<$_[2]> in order to e.g. redirect the action to another key.
-I<p31473> : 'clear' magic wasn't invoked when undefining an array.
-The bug is fixed as of this version.
+=back
+
+Finally, if C<< op_info => $num >> is also passed to C<wizard>, then one extra element is appended to C<@_>.
+Its nature depends on the value of C<$num> :
+
+=over 8
=item *
-B<5.10.0>
+C<VMG_OP_INFO_NAME>
-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.
+C<$_[-1]> is the current op name.
=item *
-B<5.11.x>
+C<VMG_OP_INFO_OBJECT>
-I<p32969> : 'len' magic is no longer invoked when calling C<length> with a magical scalar.
+C<$_[-1]> is the C<B::OP> object for the current op.
-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
+
+Both result in a small performance hit, but just getting the name is lighter than getting the op object.
+
+These callbacks are executed in scalar context and are expected to return an integer, which is then passed straight to the perl magic API.
+However, only the return value of the I<len> magic callback currently holds a meaning.
=back
-=head1 CONSTANTS
+Each callback can be specified as :
+
+=over 4
+
+=item *
+
+a code reference, which will be called as a subroutine.
+
+=item *
+
+a string reference, where the string denotes which subroutine is to be called when magic is triggered.
+If the subroutine name is not fully qualified, then the current package at the time the magic is invoked will be used instead.
+
+=item *
-=head2 C<SIG_MIN>
+a reference to C<undef>, in which case a no-op magic callback is installed instead of the default one.
+This may especially be helpful for I<local> magic, where an empty callback prevents magic from being copied during localization.
-The minimum integer used as a signature for user-defined magic.
+=back
+
+Note that I<free> magic is never called during global destruction, as there is no way to ensure that the wizard object and the callback were not destroyed before the variable.
-=head2 C<SIG_MAX>
+Here is a simple usage example :
-The maximum integer used as a signature for user-defined magic.
+ # 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" },
+ );
-=head2 C<SIG_NBR>
+=cut
- SIG_NBR = SIG_MAX - SIG_MIN + 1
+sub wizard {
+ if (@_ % 2) {
+ require Carp;
+ Carp::croak('Wrong number of arguments for wizard()');
+ }
+
+ my %opts = @_;
+
+ 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;
+
+ my ($wiz, $err);
+ {
+ local $@;
+ $wiz = eval { _wizard(map $opts{$_}, @keys) };
+ $err = $@;
+ }
+ if ($err) {
+ $err =~ s/\sat\s+.*?\n//;
+ require Carp;
+ Carp::croak($err);
+ }
+
+ return $wiz;
+}
+
+=head2 C<cast>
+
+ cast [$@%&*]var, $wiz, @args
+
+This function associates C<$wiz> magic to the supplied variable, without overwriting any other kind of magic.
+It returns true on success or when C<$wiz> magic is already attached, and croaks on error.
+When C<$wiz> provides a data constructor, it is called just before magic is cast onto the variable, and it receives a reference to the target variable in C<$_[0]> and the content of C<@args> in C<@_[1 .. @args]>.
+Otherwise, C<@args> is ignored.
+
+ # Casts $wiz onto $x, passing (\$x, '1') to the data constructor.
+ my $x;
+ cast $x, $wiz, 1;
+
+The C<var> argument can be an array or hash value.
+Magic for these scalars behaves like for any other, 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 $ENV{TZ}, wizard set => sub { POSIX::tzset(); () };
+
+If you want to handle the possible deletion of the C<'TZ'> entry, you must also specify I<store> magic.
+
+=head2 C<getdata>
+
+ getdata [$@%&*]var, $wiz
+
+This accessor fetches the private data associated with the magic C<$wiz> in the variable.
+It croaks when C<$wiz> does 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 data attached to $wiz in $x, or undef if $wiz
+ # did not attach any.
+ my $data = getdata $x, $wiz;
+
+=head2 C<dispell>
+
+ dispell [$@%&*]variable, $wiz
+
+The exact opposite of L</cast> : it dissociates C<$wiz> magic from the variable.
+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.
+ die 'no such magic in $x' unless dispell $x, $wiz;
+
+=head1 CONSTANTS
=head2 C<MGf_COPY>
-Evaluates to true iff the 'copy' magic is available.
+Evaluates to true if and only if the I<copy> magic is available.
+This is the case for perl 5.7.3 and greater, which is ensured by the requirements of this module.
=head2 C<MGf_DUP>
-Evaluates to true iff the 'dup' magic is available.
+Evaluates to true if and only if the I<dup> magic is available.
+This is the case for perl 5.7.3 and greater, which is ensured by the requirements of this module.
=head2 C<MGf_LOCAL>
-Evaluates to true iff the 'local' magic is available.
+Evaluates to true if and only if the I<local> magic is available.
+This is the case for perl 5.9.3 and greater.
=head2 C<VMG_UVAR>
-When this constant is true, you can use the C<fetch,store,exists,delete> callbacks on hashes.
+When this constant is true, you can use the I<fetch>, I<store>, I<exists> and I<delete> magics on hashes.
+Initial L</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_SCALAR_LENGTH_NOLEN>
+
+True for perls that don't call I<len> magic when taking the C<length> of a magical scalar.
+
+=head2 C<VMG_COMPAT_SCALAR_NOLEN>
+
+True for perls that don't call I<len> magic on scalars.
+Implies L</VMG_COMPAT_SCALAR_LENGTH_NOLEN>.
=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.
+True for perls that don't call I<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 I<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 you unshift in void context an element in a magical array.
+True for perls that don't call I<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.
+True for perls that call I<clear> magic when undefining magical arrays.
-=head2 C<VMG_COMPAT_SCALAR_LENGTH_NOLEN>
+=head2 C<VMG_COMPAT_HASH_DELETE_NOUVAR_VOID>
+
+True for perls that don't call I<delete> magic when you delete an element from a hash in void context.
+
+=head2 C<VMG_COMPAT_GLOB_GET>
-True for perls that don't call 'len' magic when taking the C<length> of a magical scalar.
+True for perls that call I<get> magic for operations on globs.
=head2 C<VMG_PERL_PATCHLEVEL>
=head2 C<VMG_THREADSAFE>
-True iff this module could have been built with thread-safety features enabled.
+True if and only if this module could have been built with thread-safety features enabled.
-=head1 FUNCTIONS
+=head2 C<VMG_FORKSAFE>
-=cut
+True if and only if this module could have been built with fork-safety features enabled.
+This is always true except on Windows where it is false for perl 5.10.0 and below.
-BEGIN {
- require XSLoader;
- XSLoader::load(__PACKAGE__, $VERSION);
-}
+=head2 C<VMG_OP_INFO_NAME>
-=head2 C<wizard>
+Value to pass with C<op_info> to get the current op name in the magic callbacks.
- wizard sig => ...,
- data => sub { ... },
- get => sub { my ($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 => $bool
-
-This function creates a 'wizard', an opaque type that holds the magic information.
-It takes a list of keys / values as argument, whose keys can be :
+=head2 C<VMG_OP_INFO_OBJECT>
-=over 4
+Value to pass with C<op_info> to get a C<B::OP> object representing the current op in the magic callbacks.
-=item *
+=head1 COOKBOOK
-C<sig>
+=head2 Associate an object to any perl variable
-The numerical signature.
-If not specified or undefined, a random signature is generated.
-If the signature matches an already defined magic, then the existant magic object is returned.
+This technique can be useful for passing user data through limited APIs.
+It is similar to using inside-out objects, but without the drawback of having to implement a complex destructor.
-=item *
+ {
+ package Magical::UserData;
-C<data>
+ use Variable::Magic qw<wizard cast getdata>;
-A code reference to a private data constructor.
-It is called each time this magic is cast on a variable, and the scalar returned is used as private data storage for it.
-C<$_[0]> is a reference to the magic object and C<@_[1 .. @_-1]> are all extra arguments that were passed to L</cast>.
+ my $wiz = wizard data => sub { \$_[1] };
-=item *
+ 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;
+ }
+ }
-C<get>, C<set>, C<len>, C<clear>, C<free>, C<copy>, C<local>, C<fetch>, C<store>, C<exists> and C<delete>
+ {
+ BEGIN { *ud = \&Magical::UserData::ud }
-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).
-Other arguments are specific to the magic hooked :
+ my $cb;
+ $cb = sub { print 'Hello, ', ud(&$cb), "!\n" };
-=over 8
+ ud(&$cb) = 'world';
+ $cb->(); # Hello, world!
+ }
-=item *
+=head2 Recursively cast magic on datastructures
-C<len>
+C<cast> can be called from any magical callback, and in particular from C<data>.
+This allows you to recursively cast magic on datastructures :
-When the variable is an array, C<$_[2]> contains the normal length.
-The callback is also expected to return the new scalar or array length.
+ 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";
+ ();
+ };
-=item *
+ {
+ my %h = (
+ a => [ 1, 2 ],
+ b => { c => 3 }
+ );
+ cast %h, $wiz;
+ }
-C<copy>
+When C<%h> goes out of scope, this prints something among the lines of :
-C<$_[2]> is a either a copy or an alias of the current key, which means that it is useless to try to change or cast magic on it.
-C<$_[3]> is an alias to the current element (i.e. the value).
+ free HASH at depth 0
+ free HASH at depth 1
+ free SCALAR at depth 2
+ free ARRAY at depth 1
+ free SCALAR at depth 3
+ free SCALAR at depth 3
-=item *
+Of course, this example does nothing with the values that are added after the C<cast>.
-C<fetch>, C<store>, C<exists> and C<delete>
+=head1 PERL MAGIC HISTORY
-C<$_[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.
-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.
+The places where magic is invoked have changed a bit through perl history.
+Here is a little list of the most recent ones.
-=back
+=over 4
-All the callbacks are expected to return an integer, which is passed straight to the perl magic API.
-However, only the return value of the C<len> callback currently holds a meaning.
+=item *
-=back
+B<5.6.x>
- # 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" }
+I<p14416> : I<copy> and I<dup> magic.
-=cut
+=item *
-sub wizard {
- croak 'Wrong number of arguments for wizard()' if @_ % 2;
- my %opts = @_;
- my @keys = qw/sig data 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;
- }
- return $ret;
-}
+B<5.8.9>
-=head2 C<gensig>
+I<p28160> : Integration of I<p25854> (see below).
-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.
+I<p32542> : Integration of I<p31473> (see below).
- # Generate a signature
- my $sig = gensig;
+=item *
-=head2 C<getsig>
+B<5.9.3>
- getsig $wiz
+I<p25854> : I<len> magic is no longer called when pushing an element into a magic array.
-This accessor returns the magic signature of this wizard.
+I<p26569> : I<local> magic.
- # Get $wiz signature
- my $sig = getsig $wiz;
+=item *
-=head2 C<cast>
+B<5.9.5>
- cast [$@%&*]var, [$wiz|$sig], ...
+I<p31064> : Meaningful I<uvar> magic.
-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.
-If the variable isn't a hash, any C<uvar> callback of the wizard is safely ignored.
+I<p31473> : I<clear> magic was not invoked when undefining an array.
+The bug is fixed as of this version.
- # Casts $wiz onto $x. If $wiz isn't a signature, undef can't be returned.
- my $x;
- die 'error' unless cast $x, $wiz;
+=item *
-=head2 C<getdata>
+B<5.10.0>
- getdata [$@%&*]var, [$wiz|$sig]
+Since C<PERL_MAGIC_uvar> is uppercased, C<hv_magic_check()> triggers I<copy> magic on hash stores for (non-tied) hashes that also have I<uvar> magic.
-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.
+=item *
- # Get the attached data.
- my $data = getdata $x, $wiz or die 'no such magic or magic has no data';
+B<5.11.x>
-=head2 C<dispell>
+I<p32969> : I<len> magic is no longer invoked when calling C<length> with a magical scalar.
- dispell [$@%&*]variable, [$wiz|$sig]
+I<p34908> : I<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>.
-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).
+I<g9cdcb38b> : I<len> magic is called again when pushing into a magical array in non-void context.
- # Dispell now. If $wiz isn't a signature, undef can't be returned.
- die 'no such magic or error' unless dispell $x, $wiz;
+=back
=head1 EXPORT
-The functions L</wizard>, L</gensig>, L</getsig>, L</cast>, L</getdata> and L</dispell> are only exported on request.
+The functions L</wizard>, L</cast>, L</getdata> and L</dispell> are only exported on request.
All of them are exported by the tags C<':funcs'> and C<':all'>.
-The constants L</SIG_MIN>, L</SIG_MAX>, L</SIG_NBR>, L</MGf_COPY>, L</MGf_DUP>, L</MGf_LOCAL> and L</VMG_UVAR> are also only exported on request.
-They are all exported by the tags C<':consts'> and C<':all'>.
+All the constants are also only exported on request, either individually or by the tags C<':consts'> and C<':all'>.
=cut
-use base qw/Exporter/;
+use base qw<Exporter>;
our @EXPORT = ();
our %EXPORT_TAGS = (
- 'funcs' => [ qw/wizard gensig getsig cast getdata dispell/ ],
- 'consts' => [ qw/SIG_MIN SIG_MAX SIG_NBR MGf_COPY MGf_DUP MGf_LOCAL VMG_UVAR/,
- qw/VMG_COMPAT_ARRAY_PUSH_NOLEN VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID VMG_COMPAT_ARRAY_UNDEF_CLEAR/,
- qw/VMG_COMPAT_SCALAR_LENGTH_NOLEN/,
- qw/VMG_PERL_PATCHLEVEL/,
- qw/VMG_THREADSAFE/ ]
+ 'funcs' => [ qw<wizard cast getdata dispell> ],
+ 'consts' => [ qw<
+ MGf_COPY MGf_DUP MGf_LOCAL VMG_UVAR
+ VMG_COMPAT_SCALAR_LENGTH_NOLEN
+ VMG_COMPAT_SCALAR_NOLEN
+ VMG_COMPAT_ARRAY_PUSH_NOLEN VMG_COMPAT_ARRAY_PUSH_NOLEN_VOID
+ VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID
+ VMG_COMPAT_ARRAY_UNDEF_CLEAR
+ VMG_COMPAT_HASH_DELETE_NOUVAR_VOID
+ VMG_COMPAT_GLOB_GET
+ VMG_PERL_PATCHLEVEL
+ VMG_THREADSAFE VMG_FORKSAFE
+ VMG_OP_INFO_NAME VMG_OP_INFO_OBJECT
+ > ],
);
our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
$EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
=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.
-The only way to address this would be to return a reference.
+In order to hook hash operations with magic, you need at least perl 5.10.0 (see L</VMG_UVAR>).
-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.
+If you want to store a magic object in the private data slot, you will not be able to recover the magic with L</getdata>, since magic is not copied by assignment.
+You can work around this gotcha by storing a reference to the magic object instead.
-=head1 DEPENDENCIES
+If you define a wizard with I<free> magic and cast it on itself, it results in a memory cycle, so this destructor will not be called when the wizard is freed.
-L<perl> 5.7.3.
-
-L<Carp> (standard since perl 5), L<XSLoader> (standard since perl 5.006).
+=head1 DEPENDENCIES
-Copy tests need L<Tie::Array> (standard since perl 5.005) and L<Tie::Hash> (since 5.002).
+L<perl> 5.8.
-Some uvar tests need L<Hash::Util::FieldHash> (standard since perl 5.009004).
+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.
-Glob tests need L<Symbol> (standard since perl 5.002).
+L<Carp> (core since perl 5), L<XSLoader> (since 5.6.0).
-Threads tests need L<threads> and L<threads::shared>.
+Copy tests need L<Tie::Array> (core since perl 5.005) and L<Tie::Hash> (since 5.002).
+Some uvar tests need L<Hash::Util::FieldHash> (since 5.9.4).
+Glob tests need L<Symbol> (since 5.002).
+Threads tests need L<threads> and L<threads::shared> (both since 5.7.3).
=head1 SEE ALSO
=head1 BUGS
-Please report any bugs or feature requests to C<bug-variable-magic at rt.cpan.org>, or through the web interface at L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Variable-Magic>. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
+Please report any bugs or feature requests to C<bug-variable-magic at rt.cpan.org>, or through the web interface at L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Variable-Magic>.
+I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
=head1 SUPPORT
=head1 COPYRIGHT & LICENSE
-Copyright 2007-2009 Vincent Pit, all rights reserved.
+Copyright 2007,2008,2009,2010,2011,2012 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