Variable::Magic - Associate user-defined magic to variables from Perl.
VERSION
- Version 0.22
+ Version 0.53
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"
+ }
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 $!, $( or $^W, the %ENV and %SIG hashes, the @ISA array, "vec()"
+ and "substr()" lvalues, threads::shared variables... They all share the
+ same underlying C API, and this module gives you direct access to it.
+
+ Still, the magic made available by this module differs from tieing and
+ overloading in several ways :
+
+ * Magic is not copied on assignment.
+
+ You attach it to variables, not values (as for blessed references).
+
+ * Magic does not replace the original semantics.
- Magic differs from tieing and overloading in several ways :
+ 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 "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 isn't copied on assignation (as for blessed references) : you
- attach it to variables, not values.
+ * Magic is multivalued.
- * It doesn't replace the original semantics : magic callbacks trigger
- before the original action take place, and can't prevent it to
- happen.
+ You can safely apply different kinds of magics to the same variable,
+ and each of them will be invoked successively.
- * It's mostly invisible at the Perl level : magical and non-magical
- variables cannot be distinguished with "ref", "reftype" or another
- trick.
+ * Magic is type-agnostic.
- * It's notably faster, since perl's way of handling magic is lighter
- by nature, and there's no need for any method resolution.
+ 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.
+
+ * Magic is invisible at Perl level.
+
+ Magical and non-magical variables cannot be distinguished with
+ "ref", "tied" or another trick.
+
+ * 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.
The operations that can be overloaded are :
- * "get"
+ * *get*
+
+ This magic is invoked when the variable is evaluated. It is never
+ called for arrays and hashes.
- This magic is invoked when the variable is evaluated (does not
- include array/hash subscripts and slices).
+ * *set*
- * "set"
+ This magic is called each time the value of the variable changes. It
+ is called for array subscripts and slices, but never for hashes.
- This one is triggered each time the value of the variable changes
- (includes array/hash subscripts and slices).
+ * *len*
- * "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 ("for", "map" or "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 ("for", "map" or "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
+ "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
+ "VMG_COMPAT_SCALAR_LENGTH_NOLEN" and "VMG_COMPAT_SCALAR_NOLEN" to
+ see if this magic is available for scalars or not.
- * "clear"
+ * *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
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"
+ * *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. "DESTROY" methods),
+ except that exceptions thrown from inside a *free* callback will
+ always be propagated to the surrounding code.
- * "copy"
+ * *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.
+ This magic only applies to tied arrays and hashes, and fires when
+ you try to access or change their elements.
- * "dup"
+ * *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.
- * "local"
+ * *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.
+ perl if and only if "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.
+ The following actions only apply to hashes and are available if and only
+ if "VMG_UVAR" is true. They are referred to as *uvar* magics.
- * "fetch"
+ * *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.
- * "store"
+ * *store*
This one is called when an element is stored into the hash.
- * "exists"
+ * *exists*
This magic fires when a key is tested for existence in the hash.
- * "delete"
+ * *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.
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).
+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 ],
+ )
+
+ 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 :
-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.
+ * "data"
- * 5.6.x
+ 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 $_[0] being a reference to this variable and @_[1 ..
+ @_-1] being all extra arguments that were passed to "cast". The
+ scalar returned from this call is then attached to the variable and
+ can be retrieved later with "getdata".
- *p14416* : 'copy' and 'dup' magic.
+ * "get", "set", "len", "clear", "free", "copy", "local", "fetch",
+ "store", "exists" and "delete"
- * 5.9.3
+ 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.
- *p25854* : 'len' magic is no longer called when pushing an element
- into a magic array.
+ When those callbacks are executed, $_[0] is a reference to the magic
+ variable and $_[1] is the associated private data (or "undef" when
+ no private data constructor is supplied with the wizard). Other
+ arguments depend on which kind of magic is involved :
- *p26569* : 'local' magic.
+ * *len*
- * 5.9.5
+ $_[2] contains the natural, non-magical length of the
+ variable (which can only be a scalar or an array as *len*
+ magic is only relevant for these types). The callback is
+ expected to return the new scalar or array length to use, or
+ "undef" to default to the normal length.
- *p31064* : Meaningful 'uvar' magic.
+ * *copy*
- *p31473* : 'clear' magic wasn't invoked when undefining an array.
- The bug is fixed as of this version.
+ $_[2] is a either an alias or a copy of the current key, and
+ $_[3] is an alias to the current element (i.e. the value).
+ Because $_[2] might be a copy, it is useless to try to
+ change it or cast magic on it.
- * 5.10.0
+ * *fetch*, *store*, *exists* and *delete*
- Since "PERL_MAGIC_uvar" is uppercased, "hv_magic_check()" triggers
- 'copy' magic on hash stores for (non-tied) hashes that also have
- 'uvar' magic.
+ $_[2] is an alias to the current key. Note that $_[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 "copy_key => 1" to "wizard" which, at the
+ price of a small performance hit, allows you to safely
+ assign to $_[2] in order to e.g. redirect the action to
+ another key.
- * 5.11.x
+ Finally, if "op_info => $num" is also passed to "wizard", then one
+ extra element is appended to @_. Its nature depends on the value of
+ $num :
- *p32969* : 'len' magic is no longer invoked when calling "length"
- with a magical scalar.
+ * "VMG_OP_INFO_NAME"
-CONSTANTS
- "SIG_MIN"
- The minimum integer used as a signature for user-defined magic.
+ $_[-1] is the current op name.
+
+ * "VMG_OP_INFO_OBJECT"
+
+ $_[-1] is the "B::OP" object for the current op.
+
+ 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 *len* magic callback
+ currently holds a meaning.
+
+ 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* 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.
+
+ Here is 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" },
+ );
+
+ "cast"
+ cast [$@%&*]var, $wiz, @args
+
+ This function associates $wiz magic to the supplied variable, without
+ overwriting any other kind of magic. It returns true on success or when
+ $wiz magic is already attached, and croaks on error. When $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 $_[0]
+ and the content of @args in @_[1 .. @args]. Otherwise, @args is ignored.
+
+ # Casts $wiz onto $x, passing (\$x, '1') to the data constructor.
+ my $x;
+ cast $x, $wiz, 1;
+
+ The "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
+ "POSIX::tzset" each time the 'TZ' environment variable is changed in
+ %ENV, you can use :
- "SIG_MAX"
- The maximum integer used as a signature for user-defined magic.
+ use POSIX;
+ cast $ENV{TZ}, wizard set => sub { POSIX::tzset(); () };
- "SIG_NBR"
- SIG_NBR = SIG_MAX - SIG_MIN + 1
+ If you want to handle the possible deletion of the 'TZ' entry, you must
+ also specify *store* magic.
+ "getdata"
+ getdata [$@%&*]var, $wiz
+
+ This accessor fetches the private data associated with the magic $wiz in
+ the variable. It croaks when $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, $wiz;
+
+ "dispell"
+ dispell [$@%&*]variable, $wiz
+
+ The exact opposite of "cast" : it dissociates $wiz magic from the
+ variable. This function returns true on success, 0 when no magic
+ represented by $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;
+
+CONSTANTS
"MGf_COPY"
- Evaluates to true iff the 'copy' magic is available.
+ Evaluates to true if and only if the *copy* magic is available. This is
+ the case for perl 5.7.3 and greater, which is ensured by the
+ requirements of this module.
"MGf_DUP"
- Evaluates to true iff the 'dup' magic is available.
+ Evaluates to true if and only if the *dup* magic is available. This is
+ the case for perl 5.7.3 and greater, which is ensured by the
+ requirements of this module.
"MGf_LOCAL"
- Evaluates to true iff the 'local' magic is available.
+ Evaluates to true if and only if the *local* magic is available. This is
+ the case for perl 5.9.3 and greater.
"VMG_UVAR"
- When this constant is true, you can use the "fetch,store,exists,delete"
- callbacks on hashes.
+ When this constant is true, you can use the *fetch*, *store*, *exists*
+ and *delete* magics 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_SCALAR_NOLEN"
+ True for perls that don't call *len* magic on scalars. Implies
+ "VMG_COMPAT_SCALAR_LENGTH_NOLEN".
"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 *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.
+
+ "VMG_COMPAT_ARRAY_PUSH_NOLEN_VOID"
+ True for perls that don't call *len* magic when you push in void context
+ an element in a magical array.
+
+ "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.
"VMG_COMPAT_ARRAY_UNDEF_CLEAR"
- True for perls that call 'clear' magic when undefining magical arrays.
+ 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* 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
perls.
"VMG_THREADSAFE"
- True iff this module could have been built with thread-safety features
- enabled.
-
-FUNCTIONS
- "wizard"
- 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 :
+ True if and only if this module could have been built with thread-safety
+ features enabled.
+
+ "VMG_FORKSAFE"
+ 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.
+
+ "VMG_OP_INFO_NAME"
+ Value to pass with "op_info" to get the current op name in the magic
+ callbacks.
+
+ "VMG_OP_INFO_OBJECT"
+ Value to pass with "op_info" to get a "B::OP" object representing the
+ current op in the magic callbacks.
+
+COOKBOOK
+ 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<wizard cast getdata>;
+
+ 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!
+ }
+
+ Recursively cast magic on datastructures
+ "cast" can be called from any magical callback, and in particular from
+ "data". 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 %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 "cast".
- * "sig"
-
- 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.
+PERL MAGIC HISTORY
+ The places where magic is invoked have changed a bit through perl
+ history. Here is a little list of the most recent ones.
- * "data"
+ * 5.6.x
- 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".
+ *p14416* : *copy* and *dup* magic.
- * "get", "set", "len", "clear", "free", "copy", "local", "fetch",
- "store", "exists" and "delete"
+ * 5.8.9
- 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. 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].
+ *p28160* : Integration of *p25854* (see below).
- # 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" }
+ *p32542* : Integration of *p31473* (see below).
- "gensig"
- With this tool, you can manually generate random magic signature between
- SIG_MIN and SIG_MAX inclusive. That's the way "wizard" creates them when
- no signature is supplied.
+ * 5.9.3
- # Generate a signature
- my $sig = gensig;
+ *p25854* : *len* magic is no longer called when pushing an element
+ into a magic array.
- "getsig"
- getsig $wiz
+ *p26569* : *local* magic.
- This accessor returns the magic signature of this wizard.
+ * 5.9.5
- # Get $wiz signature
- my $sig = getsig $wiz;
+ *p31064* : Meaningful *uvar* magic.
- "cast"
- cast [$@%&*]var, [$wiz|$sig], ...
-
- This function associates $wiz magic to the variable supplied, without
- 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, $wiz;
+ *p31473* : *clear* magic was not invoked when undefining an array.
+ The bug is fixed as of this version.
- "getdata"
- getdata [$@%&*]var, [$wiz|$sig]
+ * 5.10.0
- 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.
+ Since "PERL_MAGIC_uvar" is uppercased, "hv_magic_check()" triggers
+ *copy* magic on hash stores for (non-tied) hashes that also have
+ *uvar* magic.
- # Get the attached data.
- my $data = getdata $x, $wiz or die 'no such magic or magic has no data';
+ * 5.11.x
- "dispell"
- dispell [$@%&*]variable, [$wiz|$sig]
+ *p32969* : *len* magic is no longer invoked when calling "length"
+ with a magical scalar.
- The exact opposite of "cast" : it dissociates $wiz magic from the
- 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).
+ *p34908* : *len* magic is no longer called when pushing / unshifting
+ an element into a magical array in void context. The "push" part was
+ already covered by *p25854*.
- # Dispell now. If $wiz isn't a signature, undef can't be returned.
- die 'no such magic or error' unless dispell $x, $wiz;
+ *g9cdcb38b* : *len* magic is called again when pushing into a
+ magical array in non-void context.
EXPORT
- The functions "wizard", "gensig", "getsig", "cast", "getdata" and
- "dispell" are only exported on request. All of them are exported by the
- tags ':funcs' and ':all'.
+ The functions "wizard", "cast", "getdata" and "dispell" are only
+ exported on request. All of them are exported by the tags ':funcs' 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'.
+ All the constants are also only exported on request, either individually
+ or 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.
+ In order to hook hash operations with magic, you need at least perl
+ 5.10.0 (see "VMG_UVAR").
- 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.
+ If you want to store a magic object in the private data slot, you will
+ not be able to recover the magic with "getdata", since magic is not
+ copied by assignment. You can work around this gotcha by storing a
+ reference to the magic object instead.
-DEPENDENCIES
- perl 5.7.3.
-
- Carp (standard since perl 5), XSLoader (standard since perl 5.006).
+ If you define a wizard with *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.
- Copy tests need Tie::Array (standard since perl 5.005) and Tie::Hash
- (since 5.002).
+DEPENDENCIES
+ perl 5.8.
- Some uvar tests need 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 Symbol (standard since perl 5.002).
+ Carp (core since perl 5), XSLoader (since 5.6.0).
- Threads tests need threads and threads::shared.
+ Copy tests need Tie::Array (core since perl 5.005) and Tie::Hash (since
+ 5.002). Some uvar tests need Hash::Util::FieldHash (since 5.9.4). Glob
+ tests need Symbol (since 5.002). Threads tests need threads and
+ threads::shared (both since 5.7.3).
SEE ALSO
perlguts and perlapi for internal information about magic.
AUTHOR
Vincent Pit, "<perl at profvince.com>", <http://www.profvince.com>.
- You can contact me by mail or on #perl @ FreeNode (vincent or
- Prof_Vince).
+ You can contact me by mail or on "irc.perl.org" (vincent).
BUGS
Please report any bugs or feature requests to "bug-variable-magic at
<http://www.profvince.com/perl/cover/Variable-Magic>.
COPYRIGHT & LICENSE
- Copyright 2007-2008 Vincent Pit, all rights reserved.
+ Copyright 2007,2008,2009,2010,2011,2012,2013 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