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#ifndef ZSERIO_SPAN_H_INC |
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#define ZSERIO_SPAN_H_INC |
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#include <array> |
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#include <cstddef> |
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#include <limits> |
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#include <iterator> |
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#include <type_traits> |
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#include <vector> |
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namespace zserio |
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{ |
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/** |
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* Constant used to differentiate between spans of dynamic and static extent. |
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*/ |
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constexpr std::size_t dynamic_extent = std::numeric_limits<std::size_t>::max(); |
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namespace detail |
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{ |
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template <typename T, std::size_t Extent> |
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struct SpanStorage |
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{ |
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SpanStorage() = default; |
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SpanStorage(T* data, std::size_t) : |
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m_data(data) |
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{} |
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T* m_data = nullptr; |
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static constexpr std::size_t m_size = Extent; |
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}; |
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template <typename T> |
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struct SpanStorage<T, dynamic_extent> |
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{ |
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SpanStorage() = default; |
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SpanStorage(T* data, std::size_t size) : |
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m_data(data), m_size(size) |
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{} |
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T* m_data = nullptr; |
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std::size_t m_size = 0; |
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}; |
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} // namespace detail |
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/** |
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* Class that holds non-owning reference (aka. "view") to continuous sequence of objects. |
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* The user of this class is responsible of making sure, that the referenced sequence is valid |
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* as long as the instance of the Span is alive. |
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* Inspired by C++20 std::span. |
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*/ |
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template <typename T, std::size_t Extent = dynamic_extent> |
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class Span |
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{ |
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public: |
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using element_type = T; |
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using value_type = typename std::remove_cv<T>::type; |
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using size_type = std::size_t; |
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using difference_type = std::ptrdiff_t; |
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using pointer = T*; |
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using const_pointer = const T*; |
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using reference = T&; |
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using iterator = pointer; |
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using const_iterator = const_pointer; |
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using reverse_iterator = std::reverse_iterator<iterator>; |
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using const_reverse_iterator = std::reverse_iterator<const_iterator>; |
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static constexpr size_type extent = Extent; |
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/** |
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* Constructor. Initializes empty Span. |
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*/ |
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template <size_type ext = Extent, |
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typename std::enable_if<(ext == 0 || ext == dynamic_extent), int>::type = 0> |
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constexpr Span() noexcept |
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{} |
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/** |
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* Constructor. Initializes Span holding a reference starting at given pointer, having |
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* given number of elements. |
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* |
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* \param first Pointer to first element in the sequence. |
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* \param count Number of elements. |
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*/ |
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constexpr Span(pointer first, size_type count) : |
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m_storage(first, count) |
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{} |
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/** |
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* Constructor. Initializes Span holding a reference starting at given pointer, ending |
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* at another pointer. |
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* |
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* \param first Pointer to first element in the sequence. |
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* \param last Pointer to one-after-last element in the sequence. |
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*/ |
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constexpr Span(pointer first, pointer last) : |
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m_storage(first, static_cast<size_t>(last - first)) |
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{} |
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/** |
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* Constructor. Initializes Span holding a reference to array. |
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* |
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* \param arr Array to which the Span will hold a reference. |
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*/ |
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template <size_type N, size_type ext = Extent, |
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typename std::enable_if<(ext == dynamic_extent || ext == N), int>::type = 0> |
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constexpr Span(element_type(&arr)[N]) noexcept : |
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m_storage(arr, N) |
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{} |
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/** |
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* Constructor. Initializes Span holding a reference to std::array. |
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* |
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* \param arr std::array to which the Span will hold a reference. |
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*/ |
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template <typename U, size_type N, size_type ext = Extent, |
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typename std::enable_if<(ext == dynamic_extent || ext == N) && |
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std::is_convertible<U(*)[], T(*)[]>::value, int>::type = 0> |
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constexpr Span(std::array<U, N>& arr) noexcept : |
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m_storage(arr.data(), arr.size()) |
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{} |
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/** |
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* Constructor. Initializes Span holding a reference to std::array. |
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* |
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* \param arr std::array to which the Span will hold a reference. |
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*/ |
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template <typename U, size_type N, size_type ext = Extent, |
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typename std::enable_if<(ext == dynamic_extent || ext == N) && |
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std::is_convertible<const U(*)[], T(*)[]>::value, int>::type = 0> |
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constexpr Span(const std::array<U, N>& arr) noexcept : |
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m_storage(arr.data(), arr.size()) |
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{} |
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/** |
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* Constructor. Initializes Span holding a reference to std::vector. |
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* |
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* \param vec std::vector to which the Span will hold a reference. |
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*/ |
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template <typename U, typename ALLOC, size_type ext = Extent, |
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typename std::enable_if<(ext == dynamic_extent) && |
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std::is_convertible<U(*)[], T(*)[]>::value, int>::type = 0> |
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constexpr Span(std::vector<U, ALLOC>& vec) : |
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m_storage(vec.data(), vec.size()) |
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{} |
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/** |
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* Constructor. Initializes Span holding a reference to std::vector. |
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* |
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* \param vec std::vector to which the Span will hold a reference. |
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*/ |
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template <typename U, typename ALLOC, size_type ext = Extent, |
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typename std::enable_if<(ext == dynamic_extent) && |
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std::is_convertible<const U(*)[], T(*)[]>::value, int>::type = 0> |
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constexpr Span(const std::vector<U, ALLOC>& vec) : |
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m_storage(vec.data(), vec.size()) |
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{} |
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/** |
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* Constructor. Convert between spans of different types. |
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* |
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* \param s Input span. |
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*/ |
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template <typename U, size_type N, |
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typename std::enable_if<(Extent == N || Extent == dynamic_extent) && |
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std::is_convertible<U(*)[], T(*)[]>::value, int>::type = 0> |
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constexpr Span(const Span<U, N>& s) noexcept : |
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m_storage(s.data(), s.size()) |
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{} |
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/** |
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* Method generated by default. |
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* \{ |
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*/ |
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~Span() = default; |
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Span(const Span& other) noexcept = default; |
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Span& operator=(const Span& other) noexcept = default; |
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Span(Span&& other) noexcept = default; |
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Span& operator=(Span&& other) noexcept = default; |
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/** |
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* \} |
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*/ |
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/** |
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* Begin iteration. |
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* |
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* \return Iterator to the beginning of the sequence. |
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*/ |
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constexpr iterator begin() const noexcept |
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{ |
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return data(); |
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} |
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/** |
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* End iteration. |
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* |
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* \return Iterator one-past-last element of the sequence. |
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*/ |
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constexpr iterator end() const noexcept |
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{ |
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return data() + size(); |
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} |
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/** |
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* Begin reverse iteration. |
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* |
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* \return Reverse iterator to the last element. |
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*/ |
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constexpr reverse_iterator rbegin() const noexcept |
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{ |
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return reverse_iterator(end()); |
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} |
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/** |
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* End reverse iteration. |
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* |
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* \return Reverse iterator one-before-first element of the sequence. |
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*/ |
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constexpr reverse_iterator rend() const noexcept |
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{ |
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return reverse_iterator(begin()); |
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} |
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/** |
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* Get reference to the first element of the sequence. The sequence shall not be empty. |
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* |
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* \return Reference to the first element of the sequence |
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*/ |
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constexpr reference front() const |
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{ |
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return data()[0]; |
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} |
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/** |
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* Get reference to the last element of the sequence. The sequence shall not be empty. |
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* |
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* \return Reference to the last element of the sequence |
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*/ |
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constexpr reference back() const |
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{ |
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return data()[size() - 1]; |
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} |
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/** |
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* Access the element on given index. |
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* |
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* \param idx Index of element to be accessed. Must be less than size(). |
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* \return Element on given index. |
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*/ |
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constexpr reference operator[](size_type idx) const |
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{ |
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return data()[idx]; |
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} |
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/** |
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* Get pointer to the sequence beginning. |
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* |
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* \return Pointer to the sequence beginning |
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*/ |
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constexpr pointer data() const noexcept |
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{ |
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return m_storage.m_data; |
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} |
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/** |
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* Get number of elements in the sequence. |
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* |
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* \return Number of elements in the sequence. |
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*/ |
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constexpr size_type size() const noexcept |
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{ |
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return m_storage.m_size; |
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} |
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/** |
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* Get size of sequence in bytes. |
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* |
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* \return Size of sequence in bytes. |
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*/ |
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constexpr size_type size_bytes() const noexcept |
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{ |
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return size() * sizeof(element_type); |
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} |
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/** |
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* Check if the sequence is empty. |
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* |
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* \return True if the sequence is empty, false otherwise. |
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*/ |
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constexpr bool empty() const noexcept |
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{ |
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return size() == 0; |
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} |
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/** |
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* Get subspan of given number of elements from the sequence start. |
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* |
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* \return Subspan of given number of elements from the sequence start. |
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*/ |
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template <size_type Count> |
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constexpr Span<element_type, Count> first() const |
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{ |
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static_assert(Count <= Extent, "Requested number of characters out of range."); |
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return Span<element_type, Count>(data(), Count); |
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} |
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/** |
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* Get subspan of given number of elements from the sequence start. |
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* |
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* \param Count Requested number of elements in the subspan. Shall not be bigger than size(). |
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* \return Subspan of given number of elements from the sequence start. |
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*/ |
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constexpr Span<element_type, dynamic_extent> first(size_type Count) const |
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{ |
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return Span<element_type, dynamic_extent>(data(), Count); |
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} |
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/** |
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* Get subspan of given number of elements from the sequence end. |
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* |
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* \return Subspan of given number of elements from the sequence end. |
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*/ |
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template <size_type Count> |
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constexpr Span<element_type, Count> last() const |
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{ |
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static_assert(Count <= Extent, "Requested number of characters out of range."); |
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return Span<element_type, Count>(data() + (size() - Count), Count); |
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} |
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/** |
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* Get subspan of given number of elements from the sequence end. |
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* |
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* \param Count Requested number of elements in the subspan. Shall not be bigger than size(). |
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* \return Subspan of given number of elements from the sequence end. |
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*/ |
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constexpr Span<element_type, dynamic_extent> last(size_type Count) const |
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{ |
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return Span<element_type, dynamic_extent>(data() + (size() - Count), Count); |
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} |
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template <size_type Offset, size_type Count> |
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using SubspanReturnType = |
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Span<T, Count != dynamic_extent ? Count : (Extent != dynamic_extent ? Extent - Offset |
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: dynamic_extent)>; |
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/** |
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* Get subspan of given number of elements beginning at given index. |
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* |
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* \return Subspan of given number of elements beginning at given index. |
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*/ |
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/** \{ */ |
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template <size_type Offset, size_type Count = dynamic_extent, |
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typename std::enable_if<Count == dynamic_extent, int>::type = 0> |
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constexpr SubspanReturnType<Offset, Count> subspan() const |
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{ |
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static_assert((Extent == dynamic_extent) || (Offset <= Extent), |
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"Requested number of characters out of range."); |
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return SubspanReturnType<Offset, Count>(data() + Offset, size() - Offset); |
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} |
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template <size_type Offset, size_type Count, |
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typename std::enable_if<Count != dynamic_extent, int>::type = 0> |
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constexpr SubspanReturnType<Offset, Count> subspan() const |
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{ |
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static_assert((Extent == dynamic_extent) || (Offset <= Extent && Offset + Count <= Extent), |
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"Requested number of characters out of range."); |
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return SubspanReturnType<Offset, Count>(data() + Offset, Count); |
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} |
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/** \} */ |
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/** |
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* Get subspan of given number of elements beginning at given index. |
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* |
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* \param Offset Index in the original sequence, where the new subspan should start |
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* \param Count Requested number of elements in the subspan. |
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* \return Subspan of given number of elements beginning at given index. |
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*/ |
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constexpr Span<element_type, dynamic_extent> subspan(size_type Offset, |
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size_type Count = dynamic_extent) const |
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{ |
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return Span<element_type, dynamic_extent>(data() + Offset, |
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✓✓✓✓
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Count == dynamic_extent ? size() - Offset : Count ); |
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} |
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private: |
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detail::SpanStorage<T, Extent> m_storage; |
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}; |
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} // namespace zserio |
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#endif // ZSERIO_SPAN_H_INC |