XS::Object::Magic(3) Opaque, extensible XS pointer backed objects using sv_magic

SYNOPSIS


package MyObject;
use XS::Object::Magic;
sub new {
my $class = shift;
# create any object representation you like
my $self = bless {}, $class;
$self->build_struct;
return $self;
}
# or using Moose
package MyObject;
use Moose;
sub BUILD {
shift->build_struct;
}
# then in XS
MODULE = MyObject PACKAGE = MyObject
void build_struct (SV *self)
PREINIT:
my_struct_t *thingy;
CODE:
thingy = create_whatever();
/* note that we dereference self first. This
* can be done using an XS typemap of course */
xs_object_magic_attach_struct(aTHX_ SvRV(self), thingy);
void foo (SV *self)
PREINIT:
my_struct_t *thingy;
INIT:
thingy = xs_object_magic_get_struct_rv(aTHX_ self);
CODE:
my_struct_foo(thingy); /* delegate to C api */
/* using typemap */
void foo (my_struct_t *thingy)
CODE:
my_struct_foo(thingy);
/* or better yet */
PREFIX = my_struct_
void
my_struct_foo (thingy)
my_struct_t *thingy;
/* don't forget a destructor */
void
DESTROY (my_struct_t *thingy)
CODE:
Safefree(thingy);
/* note that xs_object_magic_get_struct() will
* still return a pointe which is now invalid */

DESCRPTION

This way of associating structs with Perl space objects is designed to supercede Perl's builtin "T_PTROBJ" with something that is designed to be:
Extensible
The association of the pointer using "sv_magicext" can be done on any data type, so you can associate C structs with any representation type.

This means that you can add pointers to any object (hand coded, Moose or otherwise), while still having instance data in regular hashes.

Opaque
The C pointer is neither visible nor modifiable from Perl space.

This prevents accidental corruption which could lead to segfaults using "T_PTROBJ" (e.g. "$$ptr_obj = 0").

C API

void *xs_object_magic_get_struct_rv(aTHX_ SV *sv)
When called on the object reference it will check that the "sv" is a reference, dereference it and return the associated pointer using "xs_object_magic_get_struct".

Basically the same as "xs_object_magic_get_struct(aTHX_ SvRV(sv)" but croaks if no magic was found.

Note that storing a "NULL" pointer will not cause an error.

void *xs_object_magic_get_struct(aTHX_ SV *sv)
Fetches the pointer associated with "sv".

Returns "NULL" if no pointer is found. There is no way to distinguish this from having a "NULL" pointer.

MAGIC *xs_object_magic_get_mg (aTHX_ SV *sv)
Fetches the appropriate "MAGIC" entry for the struct pointer storage from "sv".

This lets you manipulate "mg-"mg_ptr> if you need to.

void xs_object_magic_attach_struct(aTHX_ SV *sv, void *ptr)
Associates "ptr" with "sv" by adding a magic entry to "sv".
SV *xs_object_magic_create(aTHX_ void *ptr, HV *stash)
Convenience function that creates a hash object blessed to "stash" and associates it with "ptr".

Can be used to easily create a constructor: 

        SV *
        new(char *class)
                CODE:
                        RETVAL = xs_object_magic_create(
                                (void *)test_new(),
                                gv_stashpv(class, 0)
                        );
                OUTPUT: RETVAL
int xs_object_magic_has_struct(aTHX_ SV *sv)
Returns 1 if the SV has XS::Object::Magic magic, 0 otherwise.
int xs_object_magic_has_struct_rv(aTHX_ SV *self)
Returns 1 if the SV references an SV that has XS::Object::Magic magic, 0 otherwise.

This lets you write a quick predicate method, like: 

    void
    my_struct_has_struct (self)
            SV *self;
            PPCODE:
                    EXTEND(SP, 1);
                    if(xs_object_magic_has_struct_rv(aTHX_ self))
                            PUSHs(&PL_sv_yes);
                    else
                            PUSHs(&PL_sv_no);

Then you can check for the existence of your struct from the Perl side: 

    if( $object->has_struct ) { ... }
int xs_object_magic_detach_struct(aTHX_ SV *sv)
Removes the XS::Object::Magic magic from the given SV. Returns 1 if something is removed, 0 otherwise.
int xs_object_magic_detach_struct_rv(aTHX_ SV *self)
Likes "xs_object_magic_detach_struct", but takes a reference to the magic-containing SV instead of the SV itself. The reference to the SV is typically $self.

Returns 0 if the SV is not a reference, otherwise returns whatever "xs_object_magic_detach_struct" returns.

TYPEMAP

The included typemap provides a "T_PTROBJ_MG" entry which only supports the "INPUT" conversion.

This typemap entry lets you declare methods that are invoked directly on the associated pointer. In your own typemap add an entry: 

        TYPEMAP
        my_pointer_t *  T_PTROBJ_MG

and then you can use "my_pointer_t" as the argument type of the invocant: 

        I32
        method (self)
                my_pointer_t *self;
                CODE:
                        ...

Note that there is no "OUTPUT" conversion. In order to return your object you need to use ST(0) or some other means of getting the invocant.

VERSION CONTROL

<http://github.com/nothingmuch/xs-object-magic>

AUTHOR

Florian Ragwitz, Yuval Kogman

COPYRIGHT & LICENSE

        Copyright (c) 2009 Florian Ragwitz, Yuval Kogman. All rights reserved
        This program is free software; you can redistribute
        it and/or modify it under the same terms as Perl itself.

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