[C++-sig] V2: conversions through constructors?

[Peter Bienstman]

I changed 'add' to accept const Term&, but still the same behaviour..


#define BOOST_PYTHON_DYNAMIC_LIB
#define BOOST_PYTHON_V2

#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/implicit.hpp>
#include <boost/mpl/type_list.hpp>

struct T1 {};

struct Term {Term(T1&) {} };

struct Expression {void add(const Term&) {} };

BOOST_PYTHON_MODULE_INIT(m)
{
  using namespace boost::python;
  using boost::mpl::type_list;

  implicitly_convertible<T1,Term>();

  module m("m");
  
  m
    .add(class_<Expression>("Expression")
         .def("add", &Expression::add))
    .add(class_<T1>("T1"))
    .add(class_<Term>("Term")
         .def_init(type_list<T1&>()))
    ;
  
}

On Fri, 2002-04-05 at 18:24, David Abrahams wrote:
> 
> ----- Original Message -----
> From: "Peter Bienstman" <pbienst at MIT.EDU>
> 
> > Well, something like this doesn't seem to work:
> > >>> from m import *
> > >>> t1 = T1()
> > >>> e = Expression()
> > >>> e.add(t1)
> > Traceback (most recent call last):
> >   File "<stdin>", line 1, in ?
> > TypeError: bad argument type for built-in operation
> 
> 
> The corresponding C++ doesn't work either:
> 
>     T1 t1;
>     Expression e;
>     e.add(t1); // error
> 
> Because your arguments are non-const references, you're telling the
> library that they don't bind to temporaries. Thus, they require lvalue
> converters, and the converters generated by implicitly_convertible<> are
> always rvalue converters.
> 
> If you change your add() function to accept a Term const&, everything
> will work.
> 
> 
> -Dave