[EMAIL PROTECTED] (Hartmut Kaiser) writes:
> 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?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Can't you solve this by passing char instead of char& as the 4th
template parameter?
> 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;
--
Dave Abrahams
Boost Consulting
www.boost-consulting.com
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