X-Git-Url: http://git.vpit.fr/?a=blobdiff_plain;f=README;h=ac81e42c52bcf6d095d254e9dcbd72d4238ba4e6;hb=e7d06d42b01cc371aabcd4cee7ef786059ed7a1b;hp=7e89615a996e668ab39c2fa058d18332108a96c8;hpb=91932481de315250b46c30c8251490ed822ed40d;p=perl%2Fmodules%2FVariable-Magic.git diff --git a/README b/README index 7e89615..ac81e42 100644 --- a/README +++ b/README @@ -2,43 +2,99 @@ NAME Variable::Magic - Associate user-defined magic to variables from Perl. VERSION - Version 0.20 + Version 0.46 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; + + { # 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 let the user add - extra data to any variable and overload 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'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, 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 : + + * It isn't copied on assignment. + + You attach it to variables, not values (as for blessed references). + + * It doesn't replace the original semantics. + + 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. + + 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 the type of the variable. + + * It's mostly invisible at the Perl level. + + Magical and non-magical variables cannot be distinguished with + "ref", "tied" or another trick. + + * It's notably faster. + + Mainly because perl's way of handling magic is lighter by nature, + and because there's 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" - This magic is invoked when the variable is evaluated (does not - include array/hash subscripts and slices). + This magic is invoked when the variable is evaluated. It is never + called for arrays and hashes. * "set" - This one is triggered each time the value of the variable changes - (includes array/hash subscripts and slices). + This one is triggered each time the value of the variable changes. + It is called for array subscripts and slices, but never for hashes. * "len" 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 + also on array assignment and loops ("for", "map" or "grep"). The callback has then to return the length as an integer. * "clear" @@ -52,8 +108,7 @@ DESCRIPTION * "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" @@ -97,51 +152,150 @@ DESCRIPTION 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. -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. +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 ] - * 5.6.x + 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 : - *p14416* : 'copy' and 'dup' magic. + * "data" - * 5.9.3 + A code (or string) 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". - *p25854* : 'len' magic is no longer called when pushing an element - into a magic array. + * "get", "set", "len", "clear", "free", "copy", "local", "fetch", + "store", "exists" and "delete" - *p26569* : 'local' magic. + Code (or string) references to the 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). - * 5.9.5 + Moreover, when you pass "op_info => $num" to "wizard", the last + element of @_ will be the current op name if "$num == + VMG_OP_INFO_NAME" and a "B::OP" object representing the current op + if "$num == VMG_OP_INFO_OBJECT". Both have a performance hit, but + just getting the name is lighter than getting the op object. - *p31064* : Meaningful 'uvar' magic. + Other arguments are specific to the magic hooked : - *p31473* : 'clear' magic wasn't invoked when undefining an array. - The bug is fixed as of this version. + * "len" - * 5.10.0 + When the variable is an array or a scalar, $_[2] contains + the non-magical length. The callback can return the new + scalar or array length to use, or "undef" to default to the + normal length. - Since "PERL_MAGIC_uvar" is uppercased, "hv_magic_check()" triggers - 'copy' magic on hash stores for (non-tied) hashes that also have - 'uvar' magic. + * "copy" - * 5.11.x + $_[2] is a either a copy or an alias of the current key, + which means that it is useless to try to change or cast + magic on it. $_[3] is an alias to the current element (i.e. + the value). - *p32969* : 'len' magic is no longer invoked when calling "length" - with a magical scalar. + * "fetch", "store", "exists" and "delete" -CONSTANTS - "SIG_MIN" - The minimum integer used as a signature for user-defined magic. + $_[2] is an alias to the current key. Nothing prevents you + from changing it, but be aware that there lurk dangerous + side effects. For example, it may rightfully be readonly if + the key was a bareword. You can get a copy instead by + passing "copy_key => 1" to "wizard", which allows you to + safely assign to $_[2] in order to e.g. redirect the action + to another key. This however has a little performance + drawback because of the copy. + + All the callbacks are expected to return an integer, which is passed + 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. + + 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. + + 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" } + + "cast" + cast [$@%&*]var, $wiz, ... + + 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 croaks on error. All extra arguments + specified after $wiz are passed to the private data constructor in @_[1 + .. @_-1]. If the variable isn't a hash, any "uvar" callback of the + wizard is safely ignored. + + # Casts $wiz onto $x, and pass '1' to the data constructor. + my $x; + 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 + 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 $ENV{TZ}, wizard set => sub { POSIX::tzset(); () }; - "SIG_NBR" - SIG_NBR = SIG_MAX - SIG_MIN + 1 + If you want to overcome the possible deletion of the 'TZ' entry, you + have no choice but to rely on "store" uvar magic. + "getdata" + getdata [$@%&*]var, $wiz + + This accessor fetches the private data associated with the magic $wiz in + the variable. It croaks when $wiz do 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 attached data, or undef if the wizard does 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, $wiz; + +CONSTANTS "MGf_COPY" Evaluates to true iff the 'copy' magic is available. @@ -153,11 +307,21 @@ CONSTANTS "VMG_UVAR" When this constant is true, you can use the "fetch,store,exists,delete" - callbacks on hashes. + callbacks on hashes. Initial VMG_UVAR capability was introduced in perl + 5.9.5, with a fully functional implementation shipped with perl 5.10.0. "VMG_COMPAT_ARRAY_PUSH_NOLEN" True for perls that don't call 'len' magic when you push an element in a - magical array. + magical array. Starting from perl 5.11.0, this only refers to pushes in + non-void context and hence is false. + + "VMG_COMPAT_ARRAY_PUSH_NOLEN_VOID" + True for perls that don't call 'len' magic when you push in void context + an element in a magical array. + + "VMG_COMPAT_ARRAY_UNSHIFT_NOLEN_VOID" + True for perls that don't call 'len' magic when you unshift in void + context an element in a magical array. "VMG_COMPAT_ARRAY_UNDEF_CLEAR" True for perls that call 'clear' magic when undefining magical arrays. @@ -166,6 +330,9 @@ CONSTANTS True for perls that don't call 'len' magic when taking the "length" of a magical scalar. + "VMG_COMPAT_GLOB_GET" + True for perls that call 'get' magic for operations on globs. + "VMG_PERL_PATCHLEVEL" The perl patchlevel this module was built with, or 0 for non-debugging perls. @@ -174,135 +341,169 @@ CONSTANTS True iff this module could have been built with thread-safety features enabled. -FUNCTIONS - "wizard" - wizard sig => ..., - data => sub { ... }, - get => sub { my ($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) = @_; ... } + "VMG_FORKSAFE" + True iff this module could have been built with fork-safety features + enabled. This will always be true except on Windows where it's 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; + + 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 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". - 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" - - 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. - - * "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". +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. - * "get", "set", "len", "clear", "free", "copy", "local", "fetch", - "store", "exists" and "delete" + * 5.6.x - 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]. + *p14416* : 'copy' and 'dup' magic. - # 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" } + * 5.8.9 - "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. + *p28160* : Integration of *p25854* (see below). - # Generate a signature - my $sig = gensig; + *p32542* : Integration of *p31473* (see below). - "getsig" - getsig $wiz + * 5.9.3 - This accessor returns the magic signature of this wizard. + *p25854* : 'len' magic is no longer called when pushing an element + into a magic array. - # Get $wiz signature - my $sig = getsig $wiz; + *p26569* : 'local' magic. - "cast" - cast [$@%&*]var, [$wiz|$sig], ... + * 5.9.5 - 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. + *p31064* : Meaningful 'uvar' magic. - # Casts $wiz onto $x. If $wiz isn't a signature, undef can't be returned. - my $x; - die 'error' unless cast $x, $wiz; + *p31473* : 'clear' magic wasn't invoked when undefining an array. + The bug is fixed as of this version. - "getdata" - getdata [$@%&*]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 + accessible by "getdata" since it's not copied by assignment. 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. + In order to define magic on hash members, you need at least perl 5.10.0 + (see "VMG_UVAR") + DEPENDENCIES - perl 5.7.3. + 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). @@ -324,8 +525,7 @@ SEE ALSO AUTHOR Vincent Pit, "", . - 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 @@ -343,7 +543,7 @@ SUPPORT . COPYRIGHT & LICENSE - Copyright 2007-2008 Vincent Pit, all rights reserved. + Copyright 2007,2008,2009,2010,2011 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.