Variable::Magic - Associate user-defined magic to variables from Perl.
VERSION
- Version 0.01
+ Version 0.13
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!"
"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 reset is a
- result of the undefine (e.g. for an array).
+ 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 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 apply 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
+ *p25854* : 'len' magic is no longer called when pushing an element into
+ a magic array.
+ *p26569* : 'local' magic.
+
+ 5.9.5
+ *p31064* : Meaningful 'uvar' magic.
+ *p31473* : 'clear' magic wasn't invoked when undefining an array. The
+ bug is fixed as of this version.
+
+ 5.10.0
+ Since "PERL_MAGIC_uvar" is uppercased, "hv_magic_check()" triggers
+ 'copy' magic on hash stores for (non-tied) hashes that also have 'uvar'
+ magic.
+
CONSTANTS
"SIG_MIN"
The minimum integer used as a signature for user-defined magic.
"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.
+
+ "VMG_COMPAT_ARRAY_PUSH_NOLEN"
+ True for perls that don't call 'len' magic when you push an element in a
+ magical array.
+
+ "VMG_COMPAT_ARRAY_UNDEF_CLEAR"
+ True for perls that call 'clear' magic when undefining magical arrays.
+
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, $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) = @_; ... }
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. $_[2] is the current key in "copy",
+ "fetch", "store", "exists" and "delete" callbacks, although for
+ "copy" it may just be a copy of the actual key so it's useless to
+ (for example) cast magic on it. "copy" magic also receives the
+ current element (i.e. the value) in $_[3].
# 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. If the variable isn't a hash, any "uvar" callback of the
+ wizard is safely ignored.
+
+ # 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
+ (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.
- 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.
+ # 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'.
+
+CAVEATS
+ If you store a magic object in the private data slot, the magic won't be
+ accessible by "getdata" since it's not copied by assignation. The only
+ way to address this would be to return a reference.
+
+ If you define a wizard with a "free" callback and cast it on itself,
+ this destructor won't be called because the wizard will be destroyed
+ first.
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>"
+ Vincent Pit, "<perl at profvince.com>", <http://www.profvince.com>.
+
+ You can contact me by mail or on #perl @ FreeNode (vincent or
+ Prof_Vince).
BUGS
Please report any bugs or feature requests to "bug-variable-magic at
perldoc Variable::Magic
+ Tests code coverage report is available at
+ <http://www.profvince.com/perl/cover/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