#!/usr/bin/perl
package Node;
use strict;
use warnings;
use Inline C => <<'__EOI__';

// XXX no children for now
typedef struct Node {
    struct Node* parent;
    SV* sv;
} Node;

Node* new(const char * classname) {
    Node *self;

    // allocate and initialize struct
    Newx(self, 1, Node);
    self->parent = NULL;

    // create perl object and ref
    SV* perlref = newSViv((IV)self);
    SV* obj_ref = newRV_noinc(perlref);
    sv_bless(obj_ref, gv_stashpv(classname, TRUE));
    SvREADONLY_on(perlref);
    
    // store pointer to object in struct
    self->sv = obj_ref;
    return self;
}

// should NOT alter refcount
Node* set_parent(Node* self, Node* parent) {
    self->parent = parent;
    return self;
}

Node* get_parent(Node* self) {
    return self->parent;
}

// XXX get/set children deferred

void destroy_node(Node* self) {
    Safefree(self);
}

__EOI__

sub DESTROY {
    my $self = shift;
    warn "destroying $self";
    $self->destroy_node;
}

package main;
use Devel::Peek;
$|++;
my $node = Node->new;
my $parent = Node->new;

print "NODE: ";
Dump($node);
print "---\n";

print "PARENT: "; 
Dump($parent);
print "---\n";

$node->set_parent($parent);

print "FROM FIELD: ";
print Dump($node->get_parent);
print "---\n";
[download]

Here is my typemap:

TYPEMAP
Node *         NODE

INPUT
NODE
    $var = ($type)SvIV(SvRV($arg));

OUTPUT
NODE
    $arg = $var->sv;
[download]

When I run this, the following output is produced:

NODE: SV = IV(0x7fcc7b8041b8) at 0x7fcc7b8041c8
  REFCNT = 1
  FLAGS = (PADMY,ROK)
  RV = 0x7fcc79803e98
  SV = PVMG(0x7fcc790023b0) at 0x7fcc79803e98
    REFCNT = 1
    FLAGS = (OBJECT,IOK,READONLY,pIOK)
    IV = 140516178002128
    NV = 0
    PV = 0
    STASH = 0x7fcc7a004e70      "Node"
---
PARENT: SV = IV(0x7fcc7a008838) at 0x7fcc7a008848
  REFCNT = 1
  FLAGS = (PADMY,ROK)
  RV = 0x7fcc79803ce8
  SV = PVMG(0x7fcc79002770) at 0x7fcc79803ce8
    REFCNT = 1
    FLAGS = (OBJECT,IOK,READONLY,pIOK)
    IV = 140516178002208
    NV = 0
    PV = 0
    STASH = 0x7fcc7a004e70      "Node"
---
FROM FIELD: SV = UNKNOWN(0xff) (0x7fcc7a004630) at 0x7fcc79803fd0
  REFCNT = 0
  FLAGS = (TEMP)
Attempt to free unreferenced scalar: SV 0x7fcc79803fd0, Perl interpret
+er: 0x7fcc79800000 at ref.pl line 72.
---
destroying Node=SCALAR(0x7ff391803ce8) at ref.pl line 51.
destroying Node=SCALAR(0x7ff391803e98) at ref.pl line 51.
[download]

My conclusions are as follows:

1. Object instantiation works more or less as I hoped. The typemap conversion gives me back the blessed "obj_ref" from the constructor, which in turn has the reference count from "perlref", which is created from casting the pointer to Node* as an IV integer value. (Correct?).
2. Method invocation works as hoped. The getters and setters are found, the invocant is converted with the macros SvIV(SvRV()) to get the reference, then its integer value, which we then cast as Node* pointer. (Correct?).
3. The additional method argument to set_parent is also converted correctly, using the same typemapping as the invocant.
4. However, getting our parent back results in perl not knowing what to do with the parent Node*. Some sort of unknown, moribund thing comes back. This thing throws up the "Attempt to free unreferenced scalar..." warning. This part I really don't understand and I could use some help/explanation.
5. Otherwise, the intended destructor for nodes is called as intended. It doesn't give any warnings, but whether that means I've done enough to clean up after myself, I don't know. Any advice would be greatly appreciated.. I imagine that once children come in the mix I would increment their refcount in the setter, and decrement this in the destructor - which might trigger their destruction recursively.

Apologies for the long "first" post. I used to be user "rvosa" but forgot my password and lost my email address. Thanks!