[Boost-users] Using iterator_facade from base class with sub classes

From: Daniel Lidström (daniel.lidstrom_at_[hidden])
Date: 2005-10-28 05:10:22

Hello!

I have implemented the iterator_facade for a base class called DataObject.
So now I am
able to write things like this:

   boost::shared_ptr<PxyFileData> file(...);

   const DataObject& points = file->GetPoints();
   int num_points = std::distance(points.begin(), points.end()); //! random
access iterator

A DataObject acts like a tree structure. Each DataObject holds a vector of
pointers to
children, which are also DataObjects.

Now to my problem: A PxyPoint is a sub class to DataObject, and
PxyFileData::GetPoints()
returns a DataObject where all the children are PxyPoint's. Now I would like
to call a
member function, PxyPoint::PutSpCode(const char*), on each of the children,
like this:

void put_sp_code(DataObject&, const char*);

void test()
{
   shared_ptr<PxyFileData> file(...);

   DataObject& points = file->GetPoints();
   put_sp_code(points, "spcode");
}

void put_sp_code(DataObject& points, const char* code)
{
   std::for_each(points.begin(), points.end(),
      std::bind2nd(std::mem_fun(&PxyPoint::PutSpCode), code));
}

This does not compile (VC 7.1):

c:\Program Files\Microsoft Visual Studio .NET
2003\Vc7\include\algorithm(21): error C2664: 'binder2nd<_Fn2>::result_type
binder2nd<_Fn2>::operator ()(binder2nd<_Fn2>::argument_type & ) const':
cannot convert parameter 1 from 'DataObject' to
'binder2nd<_Fn2>::argument_type & '
    with
    [
        _Fn2=mem_fun1_t<void,TPunkt,const char *>
    ]
    and
    [
        _Fn2=mem_fun1_t<void,TPunkt,const char *>
    ]
    A reference that is not to 'const' cannot be bound to a non-lvalue
    c:\projects\GEOW\V12\Test\GeoTest\Model Test\ModelTest.cpp(48): see
reference to function template instantiation '_Fn1
for_each<iter,binder2nd<_Fn2> >(_InIt,_InIt,_Fn1)' being compiled
    with
    [
        _Fn1=binder2nd<mem_fun1_t<void,TPunkt,const char *> >,
        _Fn2=mem_fun1_t<void,TPunkt,const char *>,
        _InIt=iter
    ]

(error message formatted with STLTask)

Is this possible with our design? I would like to be able to do this without
having to create
a PxyPointList, that derives from DataObject and only stores PxyPoint's (my
guess is that something
like that would work with this code). 

Thanks in advance!

Regards,
Daniel