X-Git-Url: http://git.vpit.fr/?a=blobdiff_plain;f=lib%2FVariable%2FMagic.pm;h=7c866494233c59ffdd7729ad8f6a124d396282ef;hb=2ccccc5e7ea3f299777e0b67db864a1ea60688a6;hp=179605ed1be97874555348dbf3ae6da488e2a818;hpb=c9093dd650fe5e0229e16db9a60f521ec4046552;p=perl%2Fmodules%2FVariable-Magic.git
diff --git a/lib/Variable/Magic.pm b/lib/Variable/Magic.pm
index 179605e..7c86649 100644
--- a/lib/Variable/Magic.pm
+++ b/lib/Variable/Magic.pm
@@ -5,59 +5,103 @@ 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 0.57
=cut
our $VERSION;
BEGIN {
- $VERSION = '0.28';
+ $VERSION = '0.57';
}
=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;
+
+ { # 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 and C lvalues, L 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, where you have to provide fallbacks methods for all actions by usually inheriting from the correct C 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[, C or another trick.
+Magic is invisible at Perl level.
+
+Magical and non-magical variables cannot be distinguished with C][, C 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
@@ -67,414 +111,620 @@ The operations that can be overloaded are :
=item *
-C
+I
-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
+I
-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
+I
+
+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, C] creates them when no signature is supplied.
+True for perls that call I magic for operations on globs.
- # Generate a signature
- my $sig = gensig;
+=head2 C
-=head2 C
+The perl patchlevel this module was built with, or C<0> for non-debugging perls.
- getsig $wiz
+=head2 C
-This accessor returns the magic signature of this wizard.
+True if and only if this module could have been built with thread-safety features enabled.
- # Get $wiz signature
- my $sig = getsig $wiz;
+=head2 C
-=head2 C
+True if and only if this module could have been built with fork-safety features enabled.
+This is always true except on Windows where it is false for perl 5.10.0 and below.
- cast [$@%&*]var, [$wiz|$sig], ...
+=head2 C
-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 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 callback of the wizard is safely ignored.
+Value to pass with C to get the current op name in the magic callbacks.
+
+=head2 C
+
+Value to pass with C to get a C 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;
+
+ 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";
+ }
+ $$data;
+ }
+ }
+
+ {
+ BEGIN { *ud = \&Magical::UserData::ud }
+
+ my $cb;
+ $cb = sub { print 'Hello, ', ud(&$cb), "!\n" };
+
+ ud(&$cb) = 'world';
+ $cb->(); # Hello, world!
+ }
+
+=head2 Recursively cast magic on datastructures
+
+C can be called from any magical callback, and in particular from C.
+This allows you to recursively cast magic on datastructures :
+
+ my $wiz;
+ $wiz = wizard data => sub {
+ my ($var, $depth) = @_;
+ $depth ||= 0;
+ my $r = ref $var;
+ if ($r eq 'ARRAY') {
+ &cast((ref() ? $_ : \$_), $wiz, $depth + 1) for @$var;
+ } elsif ($r eq 'HASH') {
+ &cast((ref() ? $_ : \$_), $wiz, $depth + 1) for values %$var;
+ }
+ return $depth;
+ },
+ free => sub {
+ my ($var, $depth) = @_;
+ my $r = ref $var;
+ print "free $r at depth $depth\n";
+ ();
+ };
+
+ {
+ my %h = (
+ a => [ 1, 2 ],
+ b => { c => 3 }
+ );
+ cast %h, $wiz;
+ }
+
+When C<%h> goes out of scope, this prints something among the lines of :
+
+ free HASH at depth 0
+ free HASH at depth 1
+ free SCALAR at depth 2
+ free ARRAY at depth 1
+ free SCALAR at depth 3
+ free SCALAR at depth 3
+
+Of course, this example does nothing with the values that are added after the C.
+
+=head2 Delayed magic actions
+
+Starting with Variable::Magic 0.58, the return value of the magic callbacks can be used to delay the action until after the original action takes place :
+
+ my $delayed;
+ my $delayed_aux = wizard(
+ data => sub { $_[1] },
+ free => sub {
+ my ($target) = $_[1];
+ my $target_data = &getdata($target, $delayed);
+ local $target_data->{guard} = 1;
+ if (ref $target eq 'SCALAR') {
+ my $orig = $$target;
+ $$target = $target_data->{mangler}->($orig);
+ }
+ return;
+ },
+ );
+ $delayed = wizard(
+ data => sub {
+ return +{ guard => 0, mangler => $_[1] };
+ },
+ set => sub {
+ return if $_[1]->{guard};
+ my $token;
+ cast $token, $delayed_aux, $_[0];
+ return \$token;
+ },
+ );
+ my $x = 1;
+ cast $x, $delayed => sub { $_[0] * 2 };
+ $x = 2;
+ # $x is now 4
+ # But note that the delayed action only takes place at the end of the
+ # current statement :
+ my @y = ($x = 5, $x);
+ # $x is now 10, but @y is (5, 5)
- # Casts $wiz onto $x. If $wiz isn't a signature, undef can't be returned.
- my $x;
- die 'error' unless cast $x, $wiz;
+=head1 PERL MAGIC HISTORY
-=head2 C
+The places where magic is invoked have changed a bit through perl history.
+Here is a little list of the most recent ones.
- getdata [$@%&*]var, [$wiz|$sig]
+=over 4
-This accessor fetches the private data associated with the magic C<$wiz> (or the signature C<$sig>) in the variable.
-C 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, $wiz or die 'no such magic or magic has no data';
+B<5.6.x>
-=head2 C
+I : I and I magic.
- dispell [$@%&*]variable, [$wiz|$sig]
+=item *
-The exact opposite of L : 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<$wiz> could be found in the variable, and C when no magic corresponds to the given signature (in case C<$sig> was supplied).
+B<5.8.9>
+
+I : Integration of I (see below).
+
+I : Integration of I (see below).
+
+=item *
+
+B<5.9.3>
+
+I : I magic is no longer called when pushing an element into a magic array.
+
+I : I magic.
+
+=item *
+
+B<5.9.5>
- # Dispell now. If $wiz isn't a signature, undef can't be returned.
- die 'no such magic or error' unless dispell $x, $wiz;
+I : Meaningful I magic.
+
+I : I magic was not invoked when undefining an array.
+The bug is fixed as of this version.
+
+=item *
+
+B<5.10.0>
+
+Since C is uppercased, C triggers I magic on hash stores for (non-tied) hashes that also have I magic.
+
+=item *
+
+B<5.11.x>
+
+I : I magic is no longer invoked when calling C with a magical scalar.
+
+I : I magic is no longer called when pushing / unshifting an element into a magical array in void context.
+The C part was already covered by I.
+
+I : I magic is called again when pushing into a magical array in non-void context.
+
+=back
=head1 EXPORT
-The functions L, L, L, L, L and L are only exported on request.
+The functions L, L, L and L are only exported on request.
All of them are exported by the tags C<':funcs'> and C<':all'>.
-The constants L, L, L, L, L, L and L are also only exported on request.
-They are all exported by the tags C<':consts'> and C<':all'>.
+All the constants are also only exported on request, either individually or by the tags C<':consts'> and C<':all'>.
=cut
-use base qw/Exporter/;
+use base qw;
our @EXPORT = ();
our %EXPORT_TAGS = (
- 'funcs' => [ qw/wizard gensig getsig cast getdata dispell/ ],
- 'consts' => [ qw/SIG_MIN SIG_MAX SIG_NBR MGf_COPY MGf_DUP MGf_LOCAL VMG_UVAR/,
- qw/VMG_COMPAT_ARRAY_PUSH_NOLEN VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID VMG_COMPAT_ARRAY_UNDEF_CLEAR/,
- qw/VMG_COMPAT_SCALAR_LENGTH_NOLEN/,
- qw/VMG_PERL_PATCHLEVEL/,
- qw/VMG_THREADSAFE/ ]
+ 'funcs' => [ qw ],
+ 'consts' => [ qw<
+ MGf_COPY MGf_DUP MGf_LOCAL VMG_UVAR
+ VMG_COMPAT_SCALAR_LENGTH_NOLEN
+ VMG_COMPAT_SCALAR_NOLEN
+ VMG_COMPAT_ARRAY_PUSH_NOLEN VMG_COMPAT_ARRAY_PUSH_NOLEN_VOID
+ VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID
+ VMG_COMPAT_ARRAY_UNDEF_CLEAR
+ VMG_COMPAT_HASH_DELETE_NOUVAR_VOID
+ VMG_COMPAT_CODE_COPY_CLONE
+ VMG_COMPAT_GLOB_GET
+ VMG_PERL_PATCHLEVEL
+ VMG_THREADSAFE VMG_FORKSAFE
+ VMG_OP_INFO_NAME VMG_OP_INFO_OBJECT
+ > ],
);
our @EXPORT_OK = map { @$_ } 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 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).
+
+If you want to store a magic object in the private data slot, you will not be able to recover the magic with L, since magic is not copied by assignment.
+You can work around this gotcha by storing a reference to the magic object instead.
-If you define a wizard with a C callback and cast it on itself, this destructor won't be called because the wizard will be destroyed first.
+If you define a wizard with I magic and cast it on itself, it results in a memory cycle, so this destructor will not be called when the wizard is freed.
=head1 DEPENDENCIES
L 5.8.
-L (standard since perl 5), L (standard since perl 5.006).
-
-Copy tests need L (standard since perl 5.005) and L (since 5.002).
-
-Some uvar tests need L (standard since perl 5.009004).
-
-Glob tests need L (standard since perl 5.002).
+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.
-Threads tests need L and L.
+L (core since perl 5), L (since 5.6.0).
=head1 SEE ALSO
@@ -490,7 +740,8 @@ You can contact me by mail or on C (vincent).
=head1 BUGS
-Please report any bugs or feature requests to C, or through the web interface at L. 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, or through the web interface at L.
+I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
=head1 SUPPORT
@@ -502,7 +753,7 @@ Tests code coverage report is available at L