utils/ranges/empty.hpp

0001 // This file is part of the ACTS project.
0002 //
0003 // Copyright (C) 2016 CERN for the benefit of the ACTS project
0004 //
0005 // This Source Code Form is subject to the terms of the Mozilla Public
0006 // License, v. 2.0. If a copy of the MPL was not distributed with this
0007 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
0008
0009 #pragma once
0010
0011 // Project include(s)
0012 #include "detray/definitions/detail/qualifiers.hpp"
0013 #include "detray/utils/ranges/ranges.hpp"
0014
0015 namespace detray::ranges {
0016
0017 /// @brief Implements an empty view of a given type.
0018 ///
0019 /// @see https://en.cppreference.com/w/cpp/ranges/empty_view
0020 ///
0021 /// @tparam value_t type of the empty view.
0022 template <typename value_t>
0023 class empty_view : public detray::ranges::view_interface<empty_view<value_t>> {
0024  public:
0025   /// Iterator category: bidirectional
0026   using iterator_t = value_t*;
0027
0028   /// @returns @c nullptr
0029   DETRAY_HOST_DEVICE
0030   static constexpr value_t* begin() noexcept { return nullptr; }
0031
0032   /// @returns @c nullptr
0033   DETRAY_HOST_DEVICE
0034   static constexpr value_t* end() noexcept { return nullptr; }
0035
0036   /// @returns @c nullptr
0037   DETRAY_HOST_DEVICE
0038   static constexpr value_t* data() noexcept { return nullptr; }
0039
0040   /// @returns zero
0041   DETRAY_HOST_DEVICE
0042   static constexpr std::size_t size() noexcept { return 0; }
0043
0044   /// @returns @c true
0045   DETRAY_HOST_DEVICE
0046   static constexpr bool empty() noexcept { return true; }
0047
0048   /// No value contained in view
0049   /// @{
0050   DETRAY_HOST_DEVICE
0051   constexpr value_t front() const noexcept = delete;
0052
0053   DETRAY_HOST_DEVICE
0054   constexpr value_t back() const noexcept = delete;
0055
0056   DETRAY_HOST_DEVICE
0057   constexpr value_t operator[](const dindex) const noexcept = delete;
0058   /// @}
0059 };
0060
0061 namespace views {
0062
0063 template <typename value_t>
0064 using empty = empty_view<value_t>;
0065
0066 }  // namespace views
0067
0068 template <class T>
0069 inline constexpr bool enable_borrowed_range<detray::ranges::empty_view<T>> =
0070     true;
0071
0072 }  // namespace detray::ranges