libcruft-util/iterator/unequal.hpp

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/*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Copyright 2010-2018 Danny Robson <danny@nerdcruft.net>
*/
#pragma once
namespace cruft::iterator {
///////////////////////////////////////////////////////////////////////////
/// an iterator that can be infinitely incremented but never assigned.
///
/// useful for iterator ranges where the begin iterator is an output
/// iterator and hence never reaches an end point (and where we don't want
/// to engineer the client code to account for this).
template <
typename ValueT,
typename CategoryT,
typename DistanceT,
typename PointerT,
typename ReferenceT
>
struct unequal_iterator {
using value_type = ValueT;
using iterator_category = CategoryT;
using difference_type = DistanceT;
using pointer = PointerT;
using reference = ReferenceT;
unequal_iterator& operator++ ( ) { return *this; }
unequal_iterator operator++ (int) { return *this; }
};
//-------------------------------------------------------------------------
template <typename ContainerT>
auto
make_unequal_iterator (const ContainerT&)
{
using t = typename std::iterator_traits<typename ContainerT::iterator>;
return unequal_iterator<
typename t::value_type,
typename t::iterator_category,
typename t::difference_type,
typename t::pointer,
typename t::reference
> {};
};
//-------------------------------------------------------------------------
template <
typename OtherT,
typename ValueT,
typename CategoryT,
typename DistanceT,
typename PointerT,
typename ReferenceT>
constexpr bool
operator== (
const unequal_iterator<ValueT,CategoryT,DistanceT,PointerT,ReferenceT>&,
const OtherT&
) {
return false;
}
//-------------------------------------------------------------------------
template <
typename OtherT,
typename ValueT,
typename CategoryT,
typename DistanceT,
typename PointerT,
typename ReferenceT>
constexpr bool
operator== (
const OtherT&,
const unequal_iterator<ValueT,CategoryT,DistanceT,PointerT,ReferenceT>&
) {
return false;
}
}