repeat_n.hpp

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// 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_REPEAT_N_HPP
#define RANGES_V3_VIEW_REPEAT_N_HPP
 
#include <utility>
 
#include <range/v3/range_fwd.hpp>
 
#include <range/v3/iterator/default_sentinel.hpp>
#include <range/v3/range/concepts.hpp>
#include <range/v3/utility/semiregular_box.hpp>
#include <range/v3/utility/static_const.hpp>
#include <range/v3/view/facade.hpp>
 
#include <range/v3/detail/prologue.hpp>
 
namespace ranges
{
 
    // Ordinarily, a view shouldn't contain its elements. This is so that copying
    // and assigning ranges is O(1), and also so that in the event of element
    // mutation, all the copies of the range see the mutation the same way. The
    // repeat_n_view *does* own its lone element, though. This is OK because:
    //  - O(N) copying is fine when N==1 as it is in this case, and
    //  - The element is immutable, so there is no potential for incorrect
    //    semantics.
    template<typename Val>
    struct repeat_n_view : view_facade<repeat_n_view<Val>, finite>
    {
    private:
        friend range_access;
        semiregular_box_t<Val> value_;
        std::ptrdiff_t n_;
 
        struct cursor
        {
        private:
            Val const * value_;
            std::ptrdiff_t n_;
 
        public:
            cursor() = default;
            cursor(Val const & value, std::ptrdiff_t n)
              : value_(std::addressof(value))
              , n_(n)
            {}
            Val const & read() const
            {
                return *value_;
            }
            constexpr bool equal(default_sentinel_t) const
            {
                return 0 == n_;
            }
            bool equal(cursor const & that) const
            {
                return n_ == that.n_;
            }
            void next()
            {
                RANGES_EXPECT(0 != n_);
                --n_;
            }
            void prev()
            {
                ++n_;
            }
            void advance(std::ptrdiff_t n)
            {
                n_ -= n;
            }
            std::ptrdiff_t distance_to(cursor const & that) const
            {
                return n_ - that.n_;
            }
        };
        cursor begin_cursor() const
        {
            return {value_, n_};
        }
 
    public:
        repeat_n_view() = default;
        constexpr repeat_n_view(Val value, std::ptrdiff_t n)
          : value_(detail::move(value))
          , n_((RANGES_EXPECT(0 <= n), n))
        {}
        constexpr std::size_t size() const
        {
            return static_cast<std::size_t>(n_);
        }
    };
 
    namespace views
    {
        struct repeat_n_fn
        {
            template(typename Val)(
                requires copy_constructible<Val>)
            repeat_n_view<Val> operator()(Val value, std::ptrdiff_t n) const
            {
                return repeat_n_view<Val>{std::move(value), n};
            }
        };

        RANGES_INLINE_VARIABLE(repeat_n_fn, repeat_n)
    } // namespace views
} // namespace ranges
 
#include <range/v3/detail/epilogue.hpp>
#include <range/v3/detail/satisfy_boost_range.hpp>
RANGES_SATISFY_BOOST_RANGE(::ranges::repeat_n_view)
 
#endif