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124 lines
3.2 KiB
C++
124 lines
3.2 KiB
C++
/// \file
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// Range v3 library
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//
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// Copyright Eric Niebler 2013-present
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//
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// Use, modification and distribution is subject to the
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// Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// Project home: https://github.com/ericniebler/range-v3
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//
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#ifndef RANGES_V3_VIEW_REPEAT_HPP
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#define RANGES_V3_VIEW_REPEAT_HPP
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#include <utility>
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#include <range/v3/range_fwd.hpp>
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#include <range/v3/iterator/unreachable_sentinel.hpp>
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#include <range/v3/range/concepts.hpp>
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#include <range/v3/utility/semiregular_box.hpp>
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#include <range/v3/utility/static_const.hpp>
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#include <range/v3/view/facade.hpp>
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#include <range/v3/detail/prologue.hpp>
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namespace ranges
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{
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/// \addtogroup group-views
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/// @{
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// Ordinarily, a view shouldn't contain its elements. This is so that copying
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// and assigning ranges is O(1), and also so that in the event of element
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// mutation, all the copies of the range see the mutation the same way. The
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// repeat_view *does* own its lone element, though. This is OK because:
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// - O(N) copying is fine when N==1 as it is in this case, and
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// - The element is immutable, so there is no potential for incorrect
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// semantics.
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template<typename Val>
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struct repeat_view : view_facade<repeat_view<Val>, infinite>
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{
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private:
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semiregular_box_t<Val> value_;
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friend range_access;
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struct cursor
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{
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private:
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Val const * value_;
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std::ptrdiff_t n_ = 0;
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public:
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cursor() = default;
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explicit cursor(Val const & value)
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: value_(std::addressof(value))
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{}
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Val const & read() const noexcept
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{
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return *value_;
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}
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bool equal(cursor const & that) const
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{
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return n_ == that.n_;
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}
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void next()
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{
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++n_;
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}
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void prev()
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{
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--n_;
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}
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void advance(std::ptrdiff_t d)
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{
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n_ += d;
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}
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std::ptrdiff_t distance_to(cursor const & that) const
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{
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return that.n_ - n_;
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}
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};
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cursor begin_cursor() const
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{
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return cursor{value_};
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}
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unreachable_sentinel_t end_cursor() const
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{
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return unreachable;
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}
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public:
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repeat_view() = default;
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constexpr explicit repeat_view(Val value)
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: value_(detail::move(value))
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{}
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};
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namespace views
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{
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struct repeat_fn
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{
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template(typename Val)(
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requires copy_constructible<Val>)
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repeat_view<Val> operator()(Val value) const
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{
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return repeat_view<Val>{std::move(value)};
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}
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};
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/// \relates repeat_fn
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/// \ingroup group-views
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RANGES_INLINE_VARIABLE(repeat_fn, repeat)
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} // namespace views
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/// @}
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} // namespace ranges
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#include <range/v3/detail/epilogue.hpp>
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#include <range/v3/detail/satisfy_boost_range.hpp>
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RANGES_SATISFY_BOOST_RANGE(::ranges::repeat_view)
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#endif
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