Variable::Magic - Associate user-defined magic to variables from Perl.
VERSION
- Version 0.02
+ Version 0.08
SYNOPSIS
use Variable::Magic qw/wizard cast dispell/;
- my $wiz = wizard set => sub { print STDERR "now set to $_[0]!\n" };
+ my $wiz = wizard set => sub { print STDERR "now set to ${$_[0]}!\n" };
my $a = 1;
cast $a, $wiz;
$a = 2; # "now set to 2!"
prevent it to work before perl 5.9.5 - see the history).
"free"
- This last 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 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.
+
+ "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 "MGf_COPY" is true.
+
+ "dup"
+ Invoked when the variable is cloned across threads. Currently not
+ available.
+
+ "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 "MGf_LOCAL" is true.
+
+ The following actions only applies to hashes and are available iff
+ "VMG_UVAR" is true. They are referred to as "uvar" magics.
+
+ "fetch"
+ This magic happens each time an element is fetched from the hash.
+
+ "store"
+ This one is called when an element is stored into the hash.
+
+ "exists"
+ This magic fires when a key is tested for existence in the hash.
+
+ "delete"
+ This last one triggers when a key is deleted in the hash, regardless
+ of whether the key actually exists in it.
+
+ 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).
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.
+
+ 5.6.x
+ *p14416* : 'copy' and 'dup' magic.
+
5.9.3
'len' magic is no longer called when pushing an element into a magic
array.
+ *p26569* : 'local' magic.
5.9.5
- 'clear' magic wasn't invoked when undefining an array. The bug is fixed
- as of this version.
+ *p31064* : Meaningful 'uvar' magic.
+ *p31473* : 'clear' magic wasn't invoked when undefining an array. The
+ bug is fixed as of this version.
CONSTANTS
"SIG_MIN"
"SIG_NBR"
SIG_NBR = SIG_MAX - SIG_MIN + 1
+ "MGf_COPY"
+ Evaluates to true iff the 'copy' magic is available.
+
+ "MGf_DUP"
+ Evaluates to true iff the 'dup' magic is available.
+
+ "MGf_LOCAL"
+ Evaluates to true iff the 'local' magic is available.
+
+ "VMG_UVAR"
+ When this constant is true, you can use the "fetch,store,exists,delete"
+ callbacks on hashes.
+
FUNCTIONS
"wizard"
- wizard sig => .., data => ..., get => .., set => .., len => .., clear => .., free => ..
+ 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, $elt) = @_; ... },
+ local => sub { my ($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) = @_; ... }
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 :
- 'sig'
+ "sig"
The numerical signature. If not specified or undefined, a random
- signature is generated.
-
- 'data'
- A code reference to a private data constructor. It will be called
- each time this magic is cast on a variable, and the scalar returned
- will be used as private data storage for it.
-
- 'get', 'set', 'len', 'clear' and 'free'
+ signature is generated. If the signature matches an already defined
+ magic, then the existant magic object is returned.
+
+ "data"
+ 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. $_[0] is a reference to the
+ magic object and @_[1 .. @_-1] are all extra arguments that were
+ passed to "cast".
+
+ "get", "set", "len", "clear", "free", "copy", "local", "fetch", "store",
+ "exists" and "delete"
Code references to corresponding magic callbacks. You don't have to
specify all of them : the magic associated with undefined entries
- simply won't be hooked. When the magic variable is an array or a
- hash, $_[0] is a reference to it, but directly references it
- otherwise. $_[1] is the private data (or "undef" when no private
- data constructor was supplied). In the special case of "len" magic
- and when the variable is an array, $_[2] contains its normal length.
+ simply won't be hooked. In those callbacks, $_[0] is always a
+ reference to the magic object and $_[1] is always the private data
+ (or "undef" when no private data constructor was supplied). In the
+ special case of "len" magic and when the variable is an array, $_[2]
+ contains its normal length. "copy" magic receives the current
+ element (i.e. the value) in $_[2]. $_[2] is also the current key in
+ "fetch", "store", "exists" and "delete" callbacks.
# 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" }
"gensig"
With this tool, you can manually generate random magic signature between
my $sig = getsig $wiz;
"cast"
- cast [$@%&*]var, $wiz
+ cast [$@%&*]var, [$wiz|$sig], ...
This function associates $wiz magic to the variable supplied, without
- overwriting any other kind of magic. It returns true on success or when
- $wiz magic is already present, and false on error.
-
- # Casts $wiz to $x
+ overwriting any other kind of magic. You can also supply the numeric
+ signature $sig instead of $wiz. It returns true on success or when $wiz
+ magic is already present, 0 on error, and "undef" when no magic
+ corresponds to the given signature (in case $sig was supplied). All
+ extra arguments specified after $wiz are passed to the private data
+ constructor.
+
+ # Casts $wiz onto $x. If $wiz isn't a signature, undef can't be returned.
my $x;
die 'error' unless cast $x, $wiz;
"getdata"
- getdata [$@%&*]var, $wiz
+ getdata [$@%&*]var, [$wiz|$sig]
- This accessor fetches the private data associated with the magic $wiz in
- the variable. "undef" is returned when no such magic or data is found.
+ This accessor fetches the private data associated with the magic $wiz
+ (or the signature $sig) in the variable. "undef" is returned when no
+ such magic or data is found, or when $sig does not represent a current
+ valid magic object.
+
+ # Get the attached data.
+ my $data = getdata $x, $wiz or die 'no such magic or magic has no data';
"dispell"
- dispell [$@%&*]variable, $wiz
- dispell [$@%&*]variable, $sig
+ dispell [$@%&*]variable, [$wiz|$sig]
The exact opposite of "cast" : it dissociates $wiz magic from the
- variable. You can also pass the magic signature as the second argument.
- True is returned on success, and false on error or when no magic
- represented by $wiz could be found in the variable.
+ variable. You can also pass the magic signature $sig as the second
+ argument. True is returned on success, 0 on error or when no magic
+ represented by $wiz could be found in the variable, and "undef" when no
+ magic corresponds to the given signature (in case $sig was supplied).
- # Dispell now
+ # Dispell now. If $wiz isn't a signature, undef can't be returned.
die 'no such magic or error' unless dispell $x, $wiz;
EXPORT
"dispell" are only exported on request. All of them are exported by the
tags ':funcs' and ':all'.
- The constants "SIG_MIN", "SIG_MAX" and "SIG_NBR" are also only exported
- on request. They are all exported by the tags ':consts' and ':all'.
+ The constants "SIG_MIN", "SIG_MAX", "SIG_NBR", "MGf_COPY", "MGf_DUP",
+ "MGf_LOCAL" and "VMG_UVAR" are also only exported on request. They are
+ all exported by the tags ':consts' and ':all'.
DEPENDENCIES
+ perl 5.7.3.
+
Carp (standard since perl 5), XSLoader (standard since perl 5.006).
- Tests use Symbol (standard since perl 5.002).
+ Copy tests need Tie::Array (standard since perl 5.005) and Tie::Hash
+ (since 5.002).
+
+ Some uvar tests need Hash::Util::FieldHash (standard since perl
+ 5.009004).
+
+ Glob tests need Symbol (standard since perl 5.002).
SEE ALSO
perlguts and perlapi for internal information about magic.
+ perltie and overload for other ways of enhancing objects.
+
AUTHOR
Vincent Pit, "<perl at profvince.com>"
+ You can contact me by mail or on #perl @ FreeNode (Prof_Vince).
+
BUGS
Please report any bugs or feature requests to "bug-variable-magic at
rt.cpan.org", or through the web interface at
perldoc Variable::Magic
COPYRIGHT & LICENSE
- Copyright 2007 Vincent Pit, all rights reserved.
+ Copyright 2007-2008 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