David Abrahams wrote:
> >> I have a problem while using the iterator_adaptor templates
> >> in conjunction with a istreambuf_iterator<char> (an
> >> input_iterator type). The problem shows up, because the
> >> istreambuf_iterator<char>::operator*()
> >> implementation of the STL I'm using returns a value_type
> >> (char), but the dereference policy member expects to return
> >> it a reference.
> >>
> >> It seems, that there should be a similar return type deduction for
> >> the
> >> iterator_adaptor<>::operator*() function as already
> >> implemented for the
> >> iterator_adaptor<>::operator->() function.
> >
> > Regards Hartmut
>
> Which template are you having problems with? Can you post
> some code which reproduces the problem? Did you try
> explicitly specifying the iterator's reference type?
I've attached a minimal (braindead) sample, which reproduces the problem
(it does not compile).
The input_iterator used as the Base iterator of the adaptor returns a
value_type from its operator*(), but the iterator_adaptor template
expects a reference here. Surely I could solve it by adding a member of
type value_type to my policy class, using it as a buffer and the
reference to it may be returned, but isn't it better to resolve it in
the adaptor? Even more because a congruent problem, which happens often
with the operator->() is already solved through a proxy class. I believe
that the operator*() problem may be solved in a similar fashion.
Regards Hartmut
#include <iterator>
#include <boost/iterator_adaptors.hpp>
using namespace boost;
struct dummy_input_iterator
{
typedef std::input_iterator_tag iterator_category;
typedef char value_type;
typedef size_t difference_type;
typedef char * pointer;
typedef char & reference;
value_type operator*() const { return 42; }
dummy_input_iterator & operator++() { return *this; }
dummy_input_iterator operator++(int) { return *this; }
};
typedef iterator_adaptor<
dummy_input_iterator, default_iterator_policies,
char, char &, char *
> adapted_dummy_iterator;
void main()
{
adapted_dummy_iterator it, end;
char c;
while (it != end) {
c = *it;
++it;
}
}
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