Variable::Magic - Associate user-defined magic to variables from Perl.
VERSION
- Version 0.39
+ Version 0.49
SYNOPSIS
- use Variable::Magic qw/wizard cast VMG_OP_INFO_NAME/;
+ 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 $wiz = wizard(
+ set => sub { print "now set to ${$_[0]}!\n" },
+ free => sub { print "destroyed!\n" },
+ );
my $a = 1;
cast $a, $wiz;
} # "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 $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
+ print $h{banana}, "\n"; # "0" (there is no 'banana' key in %h)
$h{pear} = 1; # "key pear stored in helem"
}
DESCRIPTION
- Magic is Perl way of enhancing objects. This mechanism lets the user add
- extra data to any variable and hook syntaxical operations (such as
+ Magic is Perl's way of enhancing variables. This mechanism lets the user
+ add extra data to any variable and hook syntactical operations (such as
access, assignment or destruction) that can be applied to it. With this
module, you can add your own magic to any variable without having to
write a single line of XS.
* It doesn't replace the original semantics.
- Magic callbacks usually trigger before the original action take
- place, and can't prevent it to happen. This also makes catching
- individual events easier than with "tie", where you have to provide
- fallbacks methods for all actions by usually inheriting from the
- correct "Tie::Std*" class and overriding individual methods in your
- own class.
+ Magic callbacks usually get triggered before the original action
+ takes place, and can't prevent it from happening. This also makes
+ catching individual events easier than with "tie", where you have to
+ provide fallbacks methods for all actions by usually inheriting from
+ the correct "Tie::Std*" class and overriding individual methods in
+ your own class.
* It's type-agnostic.
You can refer to the tests to have more insight of where the different
magics are invoked.
- To prevent any clash between different magics defined with this module,
- an unique numerical signature is attached to each kind of magic (i.e.
- each set of callbacks for magic operations). At the C level, magic
- tokens owned by magic created by this module have their "mg->mg_private"
- field set to 0x3891 or 0x3892, so please don't use these magic (sic)
- numbers in other extensions.
-
FUNCTIONS
"wizard"
- wizard data => sub { ... },
- get => sub { my ($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 => $bool,
- op_info => [ 0 | VMG_OP_INFO_NAME | VMG_OP_INFO_OBJECT ]
+ wizard(
+ data => sub { ... },
+ get => sub { my ($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
straight to the perl magic API. However, only the return value of
the "len" callback currently holds a meaning.
- 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.
+ Each callback can be specified as :
+
+ * a code reference, which will be called as a subroutine.
+
+ * 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.
+
+ * a reference to "undef", in which case a no-op magic callback is
+ installed instead of the default one. This may especially be helpful
+ for 'local' magic, where an empty callback prevents magic from being
+ copied during localization.
Note that "free" callbacks are *never* called during global destruction,
as there's no way to ensure that the wizard and the "free" callback
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" },
+ );
"cast"
cast [$@%&*]var, $wiz, ...
"VMG_UVAR"
When this constant is true, you can use the "fetch,store,exists,delete"
- callbacks on hashes.
+ 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.
+
+ "VMG_COMPAT_SCALAR_LENGTH_NOLEN"
+ True for perls that don't call 'len' magic when taking the "length" of a
+ magical scalar.
"VMG_COMPAT_ARRAY_PUSH_NOLEN"
True for perls that don't call 'len' magic when you push an element in a
"VMG_COMPAT_ARRAY_UNDEF_CLEAR"
True for perls that call 'clear' magic when undefining magical arrays.
- "VMG_COMPAT_SCALAR_LENGTH_NOLEN"
- True for perls that don't call 'len' magic when taking the "length" of a
- magical scalar.
+ "VMG_COMPAT_HASH_DELETE_NOUVAR_VOID"
+ True for perls that don't call 'delete' uvar magic when you delete an
+ element from a hash in void context.
+
+ "VMG_COMPAT_GLOB_GET"
+ True for perls that call 'get' magic for operations on globs.
"VMG_PERL_PATCHLEVEL"
The perl patchlevel this module was built with, or 0 for non-debugging
COOKBOOK
Associate an object to any perl variable
- This can be useful for passing user data through limited APIs.
+ 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/;
+ use Variable::Magic qw<wizard cast getdata>;
my $wiz = wizard data => sub { \$_[1] };
my ($var) = @_;
my $data = &getdata($var, $wiz);
unless (defined $data) {
- &cast($var, $wiz);
- $data = &getdata($var, $wiz);
- die "Couldn't cast UserData magic onto the variable" unless defined $data;
+ $data = \(my $slot);
+ &cast($var, $wiz, $slot)
+ or die "Couldn't cast UserData magic onto the variable";
}
$$data;
}
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 perl 5.10.0
+ (see "VMG_UVAR")
+
DEPENDENCIES
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.
+
Carp (standard since perl 5), XSLoader (standard since perl 5.006).
Copy tests need Tie::Array (standard since perl 5.005) and Tie::Hash
<http://www.profvince.com/perl/cover/Variable-Magic>.
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