[Boost-users] Iterator adaptor interoperability

From: Kris Braun (kris_braun_at_[hidden])
Date: 2004-02-23 21:08:12

Hello,

I've spent the day trying to get my iterators working
after upgrading to 1.31.0. I'm almost there, but I
can't seem to get const and non-const versions to
compare with each other. I've tried about everything I
can think of, so I'll just post a minimal test that
fails in hopes that someone can see my mistake:

#include <iostream>
#include <list>
#include <boost/iterator/transform_iterator.hpp>

template< class Type >
struct do_nothing {
    typedef Type result_type;

    result_type operator( )( const Type& t )
        { return t; }
};

template< class Iterator >
class simple_iterator :
    public boost::transform_iterator< do_nothing< 
        typename Iterator::value_type >, Iterator >
{
  private:
    typedef boost::transform_iterator< do_nothing< 
        typename Iterator::value_type >, Iterator >
                            super_t;

  public:
                            simple_iterator( void )
                                { }

                            simple_iterator( Iterator
iter )
                                : super_t( iter )
                                { }

    template< class Iterator2 >
                            simple_iterator( 
                                    const
simple_iterator< Iterator2 >& iter )
                                : super_t( iter.base(
) )
                                { }
};

typedef std::list< int > ListType;
typedef simple_iterator< ListType::iterator >
iterator;
typedef simple_iterator< ListType::const_iterator >
const_iterator;

struct Foo {
    iterator begin( void )
        { return iterator( m.begin( ) ); }
    const_iterator end( void ) const
        { return const_iterator( m.end( ) ); }
    ListType m;
};

void foo( void )
{
    Foo f;
    for( iterator i = f.begin( ); i != f.end( ); ++i )
{ }
}

which on VC7.1 yield
src\util\test.cpp(53) : error C2678: binary '!=' : no
operator found which takes a left-hand operand of type
'iterator' (or there is no acceptable conversion)

Any help would be much appreciated!

Cheers,
Kris

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