[Swig-devel] octave: a smarter dims(void)

[Joris G. <Jor...@me...>]

Dear SWIG developers,

Somewhat recently, the following method was added in octrun.swg:

dim_vector dims(void) const {
  return dim_vector(1,1);
}

(member of octave_swig_type)

I would like to propose a smarter version of this method, i.e. one that checks if a custom dims function is available for the specific wrapped type and falls back to (1,1) upon failure.

In the project we are working on (CasADi), we have a matrix-like class with the following member:

std::vector<int> __dims__() const {
  std::vector<int> ret(2);
  ret[0] = $self->size1();
  ret[1] = $self->size2();
  return ret;
}

The change proposed below allows us to do proper concatenation ([]) with dimension checking of swig-objects that wrap this matrix class.
We have been using a custom patch for this some time now; it may be time to contribute this to SWIG trunk.

We would appreciate any comments on this.

Best regards,
   Joris Gillis


dim_vector dims(void) const {
      octave_swig_type *nc_this = const_cast < octave_swig_type *>(this);
      
      // Find the __dims__ method of this object
      member_value_pair *m = nc_this->find_member("__dims__", false);

      if (!m) return dim_vector(1,1);
      
      // Call the __dims__ method of this object
      octave_value_list inarg;
      inarg.append(nc_this->as_value());
      octave_value_list outarg = nc_this->member_invoke(m, inarg, 1);

      // __dims__ should return (at least) one output argument
      if (outarg.length() < 1) return dim_vector(1,1);
      
      if (!outarg(0).is_cell()) {
        const Cell & c=outarg(0).cell_value();
        int ndim = c.rows();

        dim_vector d;
        d.resize(ndim);
          
        // Fill in dim_vector 
        for (int k=0;k<ndim;k++) {
          const octave_value& obj = c(k,0);
          d.elem(k) = obj.int_value();
          
          // __dims__ should return a cell filled with integers
          if (error_state) return dim_vector(1,1);
        }
        return d;
      } else {
        return dim_vector(1,1);
      }
}