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Telegram/ThirdParty/range-v3/include/range/v3/view/take.hpp

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+/// \file
+// Range v3 library
+//
+//  Copyright Eric Niebler 2013-present
+//
+//  Use, modification and distribution is subject to the
+//  Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+// Project home: https://github.com/ericniebler/range-v3
+//
+
+#ifndef RANGES_V3_VIEW_TAKE_HPP
+#define RANGES_V3_VIEW_TAKE_HPP
+
+#include <type_traits>
+
+#include <range/v3/range_fwd.hpp>
+
+#include <range/v3/algorithm/min.hpp>
+#include <range/v3/functional/bind_back.hpp>
+#include <range/v3/iterator/counted_iterator.hpp>
+#include <range/v3/iterator/default_sentinel.hpp>
+#include <range/v3/range/concepts.hpp>
+#include <range/v3/range/traits.hpp>
+#include <range/v3/utility/static_const.hpp>
+#include <range/v3/view/all.hpp>
+#include <range/v3/view/view.hpp>
+
+#include <range/v3/detail/prologue.hpp>
+
+namespace ranges
+{
+    /// \addtogroup group-views
+    /// @{
+
+    template<typename Rng>
+    struct take_view : view_interface<take_view<Rng>, finite>
+    {
+    private:
+        CPP_assert(view_<Rng>);
+        Rng base_ = Rng();
+        range_difference_t<Rng> count_ = 0;
+        template<bool Const>
+        struct sentinel
+        {
+        private:
+            using Base = meta::conditional_t<Const, Rng const, Rng>;
+            using CI = counted_iterator<iterator_t<Base>>;
+            sentinel_t<Base> end_ = sentinel_t<Base>();
+
+        public:
+            sentinel() = default;
+            constexpr explicit sentinel(sentinel_t<Base> last)
+              : end_(std::move(last))
+            {}
+            template(bool Other)(
+                requires Const AND CPP_NOT(Other) AND
+                convertible_to<sentinel_t<Rng>,
+                               sentinel_t<Base>>)
+                constexpr sentinel(sentinel<Other> that)
+              : end_(std::move(that.end_))
+            {}
+            constexpr sentinel_t<Base> base() const
+            {
+                return end_;
+            }
+#ifdef RANGES_WORKAROUND_MSVC_756601
+            template<typename = void>
+#endif // RANGES_WORKAROUND_MSVC_756601
+            friend constexpr bool operator==(sentinel const & x, CI const & y)
+            {
+                return y.count() == 0 || y.base() == x.end_;
+            }
+#ifdef RANGES_WORKAROUND_MSVC_756601
+            template<typename = void>
+#endif // RANGES_WORKAROUND_MSVC_756601
+            friend constexpr bool operator==(CI const & y, sentinel const & x)
+            {
+                return y.count() == 0 || y.base() == x.end_;
+            }
+#ifdef RANGES_WORKAROUND_MSVC_756601
+            template<typename = void>
+#endif // RANGES_WORKAROUND_MSVC_756601
+            friend constexpr bool operator!=(sentinel const & x, CI const & y)
+            {
+                return y.count() != 0 && y.base() != x.end_;
+            }
+#ifdef RANGES_WORKAROUND_MSVC_756601
+            template<typename = void>
+#endif // RANGES_WORKAROUND_MSVC_756601
+            friend constexpr bool operator!=(CI const & y, sentinel const & x)
+            {
+                return y.count() != 0 && y.base() != x.end_;
+            }
+        };
+
+#if RANGES_CXX_IF_CONSTEXPR < RANGES_CXX_IF_CONSTEXPR_17
+        template<typename Take>
+        static auto begin_random_access_(Take & take, std::true_type)
+        {
+            return ranges::begin(take.base_);
+        }
+        template<typename Take>
+        static auto begin_random_access_(Take & take, std::false_type)
+        {
+            auto s = static_cast<range_difference_t<Rng>>(take.size());
+            return make_counted_iterator(ranges::begin(take.base_), s);
+        }
+        template<typename Take>
+        static auto begin_sized_(Take & take, std::true_type)
+        {
+            return begin_random_access_(
+                take, meta::bool_<random_access_range<decltype((take.base_))>>{});
+        }
+        template<typename Take>
+        static auto begin_sized_(Take & take, std::false_type)
+        {
+            return make_counted_iterator(ranges::begin(take.base_), take.count_);
+        }
+
+        template<typename Take>
+        static auto end_random_access_(Take & take, std::true_type)
+        {
+            return ranges::begin(take.base_) +
+                   static_cast<range_difference_t<Rng>>(take.size());
+        }
+        static auto end_random_access_(detail::ignore_t, std::false_type)
+        {
+            return default_sentinel;
+        }
+        template<typename Take>
+        static auto end_sized_(Take & take, std::true_type, std::false_type) // sized
+        {
+            return end_random_access_(
+                take, meta::bool_<random_access_range<decltype((take.base_))>>{});
+        }
+        static auto end_sized_(detail::ignore_t, std::false_type,
+                               std::true_type) // infinite
+        {
+            return default_sentinel;
+        }
+        static auto end_sized_(take_view & take, std::false_type, std::false_type)
+        {
+            return sentinel<false>{ranges::end(take.base_)};
+        }
+        static auto end_sized_(take_view const & take, std::false_type, std::false_type)
+        {
+            return sentinel<true>{ranges::end(take.base_)};
+        }
+#endif
+    public:
+        take_view() = default;
+
+        constexpr take_view(Rng base, range_difference_t<Rng> cnt)
+          : base_(std::move(base))
+          , count_(cnt)
+        {}
+
+        constexpr Rng base() const
+        {
+            return base_;
+        }
+
+        CPP_auto_member
+        constexpr auto CPP_fun(begin)()(
+            requires(!simple_view<Rng>()))
+        {
+#if RANGES_CXX_IF_CONSTEXPR >= RANGES_CXX_IF_CONSTEXPR_17
+            if constexpr(sized_range<Rng>)
+                if constexpr(random_access_range<Rng>)
+                    return ranges::begin(base_);
+                else
+                {
+                    // cannot always delegate to size() member on GCC with ConceptsTS
+#if defined(__cpp_concepts) && __cpp_concepts <= 201507
+                    auto s = ranges::min(
+                        static_cast<range_difference_t<Rng>>(count_),
+                        static_cast<range_difference_t<Rng>>(ranges::size(base_)));
+#else
+                    auto s = static_cast<range_difference_t<Rng>>(size());
+#endif
+                    return make_counted_iterator(ranges::begin(base_), s);
+                }
+            else
+                return make_counted_iterator(ranges::begin(base_), count_);
+#else
+            return begin_sized_(*this, meta::bool_<sized_range<Rng>>{});
+#endif
+        }
+
+        CPP_auto_member
+        constexpr auto CPP_fun(begin)()(const //
+            requires range<Rng const>)
+        {
+#if RANGES_CXX_IF_CONSTEXPR >= RANGES_CXX_IF_CONSTEXPR_17
+            if constexpr(sized_range<Rng const>)
+                if constexpr(random_access_range<Rng const>)
+                    return ranges::begin(base_);
+                else
+                {
+                    auto s = static_cast<range_difference_t<Rng>>(size());
+                    return make_counted_iterator(ranges::begin(base_), s);
+                }
+            else
+                return make_counted_iterator(ranges::begin(base_), count_);
+#else
+            return begin_sized_(*this, meta::bool_<sized_range<Rng const>>{});
+#endif
+        }
+
+        CPP_auto_member
+        constexpr auto CPP_fun(end)()(
+            requires(!simple_view<Rng>()))
+        {
+#if RANGES_CXX_IF_CONSTEXPR >= RANGES_CXX_IF_CONSTEXPR_17
+            if constexpr(sized_range<Rng>)
+                if constexpr(random_access_range<Rng>)
+                    return ranges::begin(base_) +
+                           static_cast<range_difference_t<Rng>>(size());
+                else
+                    return default_sentinel;
+            // Not to spec: Infinite ranges:
+            else if constexpr(is_infinite<Rng>::value)
+                return default_sentinel;
+            else
+                return sentinel<false>{ranges::end(base_)};
+#else
+            return end_sized_(*this, meta::bool_<sized_range<Rng>>{}, is_infinite<Rng>{});
+#endif
+        }
+
+        CPP_auto_member
+        constexpr auto CPP_fun(end)()(const //
+            requires range<Rng const>)
+        {
+#if RANGES_CXX_IF_CONSTEXPR >= RANGES_CXX_IF_CONSTEXPR_17
+            if constexpr(sized_range<Rng const>)
+                if constexpr(random_access_range<Rng const>)
+                    return ranges::begin(base_) +
+                           static_cast<range_difference_t<Rng>>(size());
+                else
+                    return default_sentinel;
+            // Not to spec: Infinite ranges:
+            else if constexpr(is_infinite<Rng const>::value)
+                return default_sentinel;
+            else
+                return sentinel<true>{ranges::end(base_)};
+#else
+            return end_sized_(
+                *this, meta::bool_<sized_range<Rng const>>{}, is_infinite<Rng const>{});
+#endif
+        }
+
+        CPP_auto_member
+        constexpr auto CPP_fun(size)()(
+            requires sized_range<Rng>)
+        {
+            auto n = ranges::size(base_);
+            return ranges::min(n, static_cast<decltype(n)>(count_));
+        }
+        CPP_auto_member
+        constexpr auto CPP_fun(size)()(const //
+            requires sized_range<Rng const>)
+        {
+            auto n = ranges::size(base_);
+            return ranges::min(n, static_cast<decltype(n)>(count_));
+        }
+    };
+
+    template<typename Rng>
+    RANGES_INLINE_VAR constexpr bool enable_borrowed_range<take_view<Rng>> = //
+        enable_borrowed_range<Rng>;
+
+#if RANGES_CXX_DEDUCTION_GUIDES >= RANGES_CXX_DEDUCTION_GUIDES_17
+    template<typename Rng>
+    take_view(Rng &&, range_difference_t<Rng>)
+        -> take_view<views::all_t<Rng>>;
+#endif
+
+    namespace views
+    {
+        struct take_base_fn
+        {
+            template(typename Rng)(
+                requires viewable_range<Rng>)
+            take_view<all_t<Rng>> operator()(Rng && rng, range_difference_t<Rng> n) const
+            {
+                return {all(static_cast<Rng &&>(rng)), n};
+            }
+        };
+
+        struct take_fn : take_base_fn
+        {
+            using take_base_fn::operator();
+
+            template(typename Int)(
+                requires detail::integer_like_<Int>)
+            constexpr auto operator()(Int n) const
+            {
+                return make_view_closure(bind_back(take_base_fn{}, n));
+            }
+        };
+
+        /// \relates take_fn
+        RANGES_INLINE_VARIABLE(take_fn, take)
+    } // namespace views
+
+    namespace cpp20
+    {
+        namespace views
+        {
+            using ranges::views::take;
+        }
+        template(typename Rng)(
+            requires view_<Rng>)
+        using take_view = ranges::take_view<Rng>;
+    } // namespace cpp20
+    /// @}
+} // namespace ranges
+
+#include <range/v3/detail/epilogue.hpp>
+#include <range/v3/detail/satisfy_boost_range.hpp>
+RANGES_SATISFY_BOOST_RANGE(::ranges::take_view)
+
+#endif