dolfin team mailing list archive

[Ola Skavhaug <skavhaug@xxxxxxxxx>]

On Thu, Mar 5, 2009 at 9:55 AM, Anders Logg <logg@xxxxxxxxx> wrote:
> - Show quoted text -
> 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.
>

I like this idea. Thanks.



> --
> Anders
>
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-- 
Ola Skavhaug