Variable::Magic - Associate user-defined magic to variables from Perl.
VERSION
- Version 0.31
+ Version 0.34
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", because the 'banana' key doesn't exist in %h
+ $h{pear} = 1; # "key pear stored in helem"
+ }
DESCRIPTION
Magic is Perl way of enhancing objects. This mechanism lets the user add
variables. It's 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, thread::shared variables... They all share the
+ 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
* It doesn't replace the original semantics.
- Magic callbacks trigger before the original action take place, and
- can't prevent it to happen. This 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 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.
* It's type-agnostic.
* "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.
+ the variable goes out of scope, but not when it is undefined.
* "copy"
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).
+ 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"
set => sub { print STDERR "set to ${$_[0]}\n" },
free => sub { print STDERR "${$_[0]} was deleted\n" }
+ Note that "free" callbacks are *never* called during global destruction,
+ as there's no way to ensure that the wizard and the "free" callback
+ weren't destroyed before the variable.
+
"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
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
+ magic is already present, and croaks on error or when no magic
+ corresponds to the given signature (in case a $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.
+ constructor in @_[1 .. @_-1]. 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.
+ # Casts $wiz onto $x, and pass '1' to the data constructor.
my $x;
- die 'error' unless cast $x, $wiz;
+ cast $x, $wiz, 1;
The "var" argument can be an array or hash value. Magic for those
behaves like for any other scalar, except that it is dispelled when the
If you want to overcome the possible deletion of the 'TZ' entry, you
have no choice but to rely on "store" uvar magic.
+ "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, $wiz;
+ }
+
+ When %h goes out of scope, this will print something among the lines of
+ :
+
+ free HASH at depth 0
+ free HASH at depth 1
+ free SCALAR at depth 2
+ free ARRAY at depth 1
+ free SCALAR at depth 3
+ free SCALAR at depth 3
+
+ Of course, this example does nothing with the values that are added
+ after the "cast".
+
"getdata"
getdata [$@%&*]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.
+ (or the signature $sig) in the variable. It croaks when $wiz or $sig do
+ not represent a current valid magic object attached to the variable, and
+ returns "undef" when the wizard has no data constructor or when the data
+ is actually "undef".
- # Get the attached data.
- my $data = getdata $x, $wiz or die 'no such magic or magic has no data';
+ # Get the attached data, or undef if the wizard does not attach any.
+ my $data = getdata $x, $wiz;
"dispell"
dispell [$@%&*]variable, [$wiz|$sig]
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).
+ argument. This function returns true on success, 0 when no magic
+ represented by $wiz or $sig could be found in the variable, and croaks
+ if the supplied wizard or signature is invalid.
- # Dispell now. If $wiz isn't a signature, undef can't be returned.
- die 'no such magic or error' unless dispell $x, $wiz;
+ # Dispell now.
+ die 'no such magic in $x' unless dispell $x, $wiz;
CONSTANTS
"SIG_MIN"
projects / perl / modules / Variable-Magic.git / blobdiff