dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Mar 05, 2009 at 09:49:58AM +0100, Ola Skavhaug wrote:
> On Thu, Mar 5, 2009 at 9:46 AM, Anders Logg <logg@xxxxxxxxx> wrote:
> > On Thu, Mar 05, 2009 at 09:36:05AM +0100, Ola Skavhaug wrote:
> >> As some might have seen from the buildbot's failures last night, we're
> >> currently implementing a nested stack based xml parser that enables
> >> the reuse of the different parsers (we call them XMLHandlers) when
> >> reading and writing data to xml files. We want to use the handlers for
> >> both input and output, and we run into problems at construction time.
> >> For instance, when writing a std::vector<uint, int> x to file, we get
> >> a const reference, and need to cast away the constness in order to
> >> construct the XMLArray object:
> >>
> >>
> >> void NewXMLFile::operator<<(const std::vector<int>& x)
> >> {
> >>   XMLArray xml_array(const_cast<std::vector<int>&>(x), *this);
> >>   xml_array.write(filename);
> >> }
> >>
> >> Does anyone object to this const_cast?
> >
> > Is this because the handlers are used both for reading and writing?
> >
> > One option would be to split it into two files, one for reading and
> > one for writing but that is inconvenient. How about instead having two
> > objects as arguments to the constructor:
> >
> >  XMLFoo(Foo* input_foo, const Foo* output_foo, NewXMLFile& parser);
> >
> > Then we need to dolfin_assert() the pointers and use the correct one
> > for input and output.
> 
> Sure, this could be done, but we'll swamp the object with pointers.
> For example, the XMLMap already has 6 non-const pointers. Your
> suggestion will double this :)
> 
> Ola

ok, how about making the input object(s) non-const and only use them
for input.

For output, we instead have static members that take const objects:

  class XMLMesh
  {
  public:


    ...

    static write(const Mesh& mesh, stream_or_whatever, uint indentation_level=0);

  };

Then XMLFile just calls XMLMesh::write(), which may in turn call
XMLMeshData::write() etc.

-- 
Anders

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