[C++-sig] lvalue converter (and other) questions

[Ralf W. Grosse-Kunstleve]

--- David Abrahams <dave at boost-consulting.com> wrote:
> > the moment (btw: the C++ language /really/ needs template typedefs):
> 
> (btw: it's pretty hard to see why from your example)

Isn't

flex<ElementType>

a lot nicer than repeating

versa<ElementType, flex_grid<> >

all the time? With:

template <typename ElementType>
typedef versa<ElementType, flex_grid<> > flex;

> If shared<E> is already exposed via class_<>, it's already done.
> In which case, consider:

Note what this struct in the referenced code is doing:

  template <typename ElementType>
  struct shared_to_flex
  {
    static PyObject* convert(shared_plain<ElementType> const& a)
    {
      using namespace boost::python;
      versa<ElementType, flex_grid<> > result(a, flex_grid<>(a.size()));
      return incref(object(result).ptr());
    }
  };

It constructs a flex<E> from a shared<E> and then uses object() to wrap it up
for Python.
Can I have a class_<shared<E> > at the same time? How could bpl.so decide what
pops up the the Python layer? I want the flex<E>. flex<E> has a large number of
associated member/regular functions that I do not wish to bind another time for
shared<E>. Look at this file to see the damage:

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/cctbx/scitbx/include/scitbx/array_family/boost_python/flex_wrapper.h?rev=1.5&content-type=text/vnd.viewcvs-markup

Note that the entire file is one large template (well, one small and one
large). In addition there is the pickle suite (file names flex_pickle_*.h in
the same directory). Currently I use this to define eight Python types (bool,
std::size_t, int, long, float, double, std::complex<double>, std::string).
Sizes of the resulting flex.so/.pyd modules:

vc70, 800k
tru64 cxx, -O2, 12M unstripped, 11M stripped
linux gcc 3.0.4, -g, 80M unstripped, 6M stripped

And that is just the beginning. I still have a bunch of custom types to wrap.
While vc70 is very tame, I will have to buy an extra harddisk for my Linux
compilations if I duplicate everything for shared<E> and flex<E>. In addition,
at the Python level there is no point at all in having the two types. One is
better.

Thanks,
Ralf


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