[C++-sig] abstract class and virtual function

[Quant Mind]

I'm running into some problem in exposing an abstract class with some
virtual functions with default implementations (no problem with pure
virtuals).
The problem seems quite trivial but I cannot get to the bottom of it.

struct rateWrap : public irate, public boost::python::wrapper<irate>
{
bool    isScalar() const;
double value() const;
//
bool    default_isScalar()    { return this->irate::isScalar(); }
double default_value()   { return this->irate::value(); }
};
//
inline bool rateWrap::isScalar() const
    {
      if(boost::python::override overfun = this->get_override("isScalar"))
#ifdef  _MSC_VER
        return boost::python::call<char const*>(overfun.ptr());
#else
        return overfun();
#endif  //  _MSC_VER
      return irate::isScalar();
    }
//
inline double rateWrap::value() const
    {
      if(boost::python::override overfun = this->get_override("value"))
#ifdef  _MSC_VER
        return boost::python::call<char const*>(overfun.ptr());
#else
        return overfun();
#endif  //  _MSC_VER
      return irate::realvalue();
    }

While the first function, returning bool, works fine :) the second one,
returning double, does not work!!! :(
I'm compiling with Microsoft Visual Studio 2005 which returns the following
error

'return' cannot convert from 'const char *' to 'double'

I don't know what is the problem, any advise?
Luca
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