[C++-sig] exposing pointers using boost

[Furkan Kuru]

My team-mate offered a shorter way
adding Node* while exposing the class Node:

class_<Node, Node*>("Node")
              .def_readwrite("value", &Node::value)
              .def_readwrite("next", &Node::next)
              .def_readwrite("prev", &Node::prev);

On 9/4/07, Roman Yakovenko <roman.yakovenko at gmail.com> wrote:
> On 9/4/07, Furkan Kuru <furkankuru at gmail.com> wrote:
> > Hello,
> >
> > Is there a way to expose structs containing pointers of their types?
>
> There is another problem here
>
> > Let's say, I have a very simple doubly-linked list.
> >
> > struct Node {
> >         Node* next;
> >         Node* prev;
> >         int value;
> > };
> >
> > I expose it like this:
> >
> > class_<Node>("Node")
> >         .def_readwrite("value", &Node::value)
> >         .def_readwrite("next", &Node::next)
> >         .def_readwrite("prev", &Node::prev);
> >
> > When I try to access the next and prev attributes of a Node instance in
> python,
> > I get this error:
> >
> > TypeError: No to_python (by-value) converter found for C++ type: struct
> Node *
>
>
> If you would have access to Py++, it would generate the right code for you.
>
> Here is cut and paste of the relevant code from the unittests:
>
>
> struct tree_node_t{
>     ...
>     tree_node_t *left;
>     ...
> };
>
> struct tree_node_t_wrapper : tree_node_t, bp::wrapper< tree_node_t > {
>    ...
>
>     static tree_node_t * get_right(tree_node_t const & inst ){
>         return inst.right;
>     }
>
>     static void set_right( tree_node_t & inst, tree_node_t * new_value ){
>         inst.right = new_value;
>     }
>
> };
>
>
>    { //::tree_node_t
>         typedef bp::class_< tree_node_t_wrapper > tree_node_t_exposer_t;
>         tree_node_t_exposer_t tree_node_t_exposer = tree_node_t_exposer_t(
> "tree_node_t", "documentation", bp::init< bp::optional<
> member_variables::pointers::tree_node_t const * > >((
> bp::arg("parent")=bp::object() ), "documentation") );
>         bp::scope tree_node_t_scope( tree_node_t_exposer );
>         tree_node_t_exposer.add_property( "right"
>                     , bp::make_function( (::tree_node_t * (*)( ::tree_node_t
> const & ))(&tree_node_t_wrapper::get_right),
> bp::return_internal_reference< >() )
>                     , bp::make_function( (void (*)( ::tree_node_t
> &,::tree_node_t * ))(&tree_node_t_wrapper::set_right),
> bp::with_custodian_and_ward_postcall< 1, 2 >() ));
>     }
>
> Pay attention to used call policies. They are very important.
>
> HTH
>
> --
> Roman Yakovenko
> C++ Python language binding
> http://www.language-binding.net/
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>


-- 
Furkan Kuru