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86 lines
2.1 KiB
C++
86 lines
2.1 KiB
C++
/// \file
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// Range v3 library
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//
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// Copyright Eric Niebler 2014-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_EMPTY_HPP
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#define RANGES_V3_VIEW_EMPTY_HPP
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#include <range/v3/range_fwd.hpp>
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#include <range/v3/view/interface.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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template<typename T>
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struct empty_view : view_interface<empty_view<T>, (cardinality)0>
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{
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static_assert(std::is_object<T>::value,
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"The template parameter to empty_view must be an object type.");
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empty_view() = default;
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static constexpr T * begin() noexcept
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{
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return nullptr;
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}
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static constexpr T * end() noexcept
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{
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return nullptr;
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}
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static constexpr std::size_t size() noexcept
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{
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return 0u;
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}
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static constexpr T * data() noexcept
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{
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return nullptr;
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}
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RANGES_DEPRECATED(
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"Replace views::empty<T>() with views::empty<T>. "
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"It is now a variable template.")
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empty_view operator()() const
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{
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return *this;
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}
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};
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template<typename T>
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RANGES_INLINE_VAR constexpr bool enable_borrowed_range<empty_view<T>> = true;
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namespace views
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{
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template<typename T>
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RANGES_INLINE_VAR constexpr empty_view<T> empty{};
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}
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namespace cpp20
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{
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namespace views
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{
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using ranges::views::empty;
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}
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template(typename T)(
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requires std::is_object<T>::value) //
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using empty_view = ranges::empty_view<T>;
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} // namespace cpp20
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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::empty_view)
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#endif
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