[boost] input_iterator_facade (was: Re: [iterator facade] Why is dereference const?)

From: Gennadiy Rozental (gennadiy.rozental_at_[hidden])
Date: 2004-05-23 05:44:47

Hi,

Here is the input_iterator_facade template (similar in nature to Vladimir's
eof_iterator ) I am using in Boost.Test development:

namespace detail {

template<typename T>
struct value_type_ident
{
    typedef T value_type;
};

template<typename T>
struct ref_type_ident
{
    typedef T reference;
};

} // namespace detail

template<
typename ImplPolicy,
typename Derived = mpl::void_,
typename ValueType = mpl::void_,
typename Reference = mpl::void_>
class input_iterator_facade
: public iterator_facade<
    typename
mpl::if_<mpl::is_void_<Derived>,input_iterator_facade<ImplPolicy>,Derived>::
type,
    typename
mpl::if_<mpl::is_void_<ValueType>,ImplPolicy,detail::value_type_ident<ValueT
ype> >::type::value_type,
    forward_traversal_tag,
    typename
mpl::if_<mpl::is_void_<Reference>,ImplPolicy,detail::ref_type_ident<Referenc
e> >::type::reference>
{
public:
    // Constructor
    explicit            input_iterator_facade( ImplPolicy const& p =
ImplPolicy() )
    : m_policy( p )
    {
        m_valid = m_policy.initialize();

        increment();
    }

    //!! copy constructor/assignment  - should we make rhs invalid after
copy??
    //!! do we need reset method?

protected: // provide access to the derived
    // Data members
    ImplPolicy          m_policy;

private:
    friend class iterator_core_access;

    // iterator facade interface implementation
    void                increment()
    {
        if( m_valid )
            m_valid = m_policy.get();
    }
    bool                equal( input_iterator_facade const& rhs ) const
    {
         return !m_valid && !rhs.m_valid || m_valid && rhs.m_valid &&
m_policy.equal( rhs.m_policy );
    }
    reference           dereference() const
    {
          return m_policy.dereference( m_valid );
    }

    // Data members
    bool                m_valid;
};

See full versions with extra comments here:

http://tinyurl.com/2x69z

There is one specific iterator implemented that used this template located
in the same directory (more coming).
I actually combine new CRTP and old policy technique here, for later allows
me to implement more functionality in common code. Is there interest in
adding this to the family of iterator helpers?

Or could I move it in boost namespace for convenience?

Gennadiy.