/*
* This file is part of the DXX-Rebirth project <http://www.dxx-rebirth.com/>.
* It is copyright by its individual contributors, as recorded in the
* project's Git history. See COPYING.txt at the top level for license
* terms and a link to the Git history.
*/
#pragma once
#include <iterator>
#include <tuple>
#include <type_traits>
#include "dxxsconf.h"
#include "ephemeral_range.h"
#include <utility>
namespace d_zip {
namespace detail {
template <typename... T>
void discard_arguments(T &&...)
{
}
template <std::size_t... N, typename... range_iterator_type>
void increment_iterator(std::tuple<range_iterator_type...> &iterator, std::index_sequence<N...>)
{
/* Order of evaluation is irrelevant, so pass the results to a
* discarding function. This permits the compiler to evaluate the
* expression elements in any order.
*/
discard_arguments(++(std::get<N>(iterator))...);
}
template <std::size_t... N, typename... range_iterator_type>
auto dereference_iterator(const std::tuple<range_iterator_type...> &iterator, std::index_sequence<N...>)
{
/* std::make_tuple is not appropriate here, because the result of
* dereferencing the iterator may be a reference, and the resulting
* tuple should store the reference, not the underlying object.
* Calling std::make_tuple would decay such references into the
* underlying type.
*
* std::tie is not appropriate here, because it captures all
* arguments as `T &`, so it fails to compile if the result of
* dereferencing the iterator is not a reference.
*/
return std::tuple<
decltype(*(std::get<N>(iterator)))...
>(*(std::get<N>(iterator))...);
}
}
}
/* This iterator terminates when the first zipped range terminates. The
* caller is responsible for ensuring that use of the zip_iterator does
* not increment past the end of any zipped range. This can be done by
* ensuring that the first zipped range is not longer than any other
* zipped range, or by ensuring that external logic stops the traversal
* before the zip_iterator increments past the end.
*
* There is no initialization time check that the below loop would be
* safe, since a check external to the zip_iterator could stop before
* undefined behaviour occurs.
for (auto i = zip_range.begin(), e = zip_range.end(); i != e; ++i)
{
if (condition())
break;
}
*/
template <typename... range_iterator_type>
class zip_iterator : std::tuple<range_iterator_type...>
{
using base_type = std::tuple<range_iterator_type...>;
protected:
/* Prior to C++17, range-based for insisted on the same type for
* `begin` and `end`, so method `end_internal` must return a full iterator,
* even though most of it is a waste. To save some work, values that are
* used for ignored fields are default-constructed (if possible)
* instead of copy-constructed from the begin iterator.
*/
template <std::size_t I, typename T>
static typename std::enable_if<std::is_default_constructible<T>::value, T>::type end_construct_ignored_element()
{
return T();
}
template <std::size_t I, typename T>
typename std::enable_if<!std::is_default_constructible<T>::value, T>::type end_construct_ignored_element() const
{
return std::get<I>(*this);
}
template <typename E0, std::size_t... N>
zip_iterator end_internal(const E0 &e0, std::index_sequence<0, N...>) const
{
return zip_iterator(e0, this->template end_construct_ignored_element<N, typename std::tuple_element<N, base_type>::type>()...);
}
using index_type = std::make_index_sequence<sizeof...(range_iterator_type)>;
public:
using base_type::base_type;
auto operator*() const
{
return d_zip::detail::dereference_iterator(*this, index_type());
}
zip_iterator &operator++()
{
d_zip::detail::increment_iterator(*this, index_type());
return *this;
}
bool operator!=(const zip_iterator &i) const
{
return std::get<0>(*this) != std::get<0>(i);
}
bool operator==(const zip_iterator &i) const
{
return !(*this != i);
}
};
template <typename range0_iterator_type, typename... rangeN_iterator_type>
class zip : zip_iterator<range0_iterator_type, rangeN_iterator_type...>
{
range0_iterator_type m_end;
public:
using range_owns_iterated_storage = std::false_type;
using iterator = zip_iterator<range0_iterator_type, rangeN_iterator_type...>;
template <typename range0, typename... rangeN>
zip(range0 &&r0, rangeN &&... rN) :
iterator(std::begin(r0), std::begin(rN)...), m_end(std::end(r0))
{
static_assert((!any_ephemeral_range<range0 &&, rangeN &&...>::value), "cannot zip storage of ephemeral ranges");
}
__attribute_warn_unused_result
iterator begin() const { return *this; }
__attribute_warn_unused_result
iterator end() const
{
return this->end_internal(m_end, typename iterator::index_type());
}
};
template <typename range0, typename... rangeN>
zip(range0 &&r0, rangeN &&... rN) -> zip<decltype(std::begin(r0)), decltype(std::begin(rN))...>;