span_impl.h

 
// Span-compatible interface for c++17 based on:
// https://github.com/tcbrindle/span
// Copyright Tristan Brindle 2018.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file ../../LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
#include "gaia/config/config.h"
 
#include <tuple>
#include <type_traits>
 
#include "gaia/core/iterator.h"
#include "gaia/core/utility.h"
 
namespace gaia {
  namespace core {
    using span_diff_type = size_t;
    using span_size_type = size_t;
  } // namespace core
 
  namespace cnt {
    template <typename T, uint32_t N>
    class sarr;
    template <typename T, uint32_t N>
    using sarray = cnt::sarr<T, N>;
  } // namespace cnt
 
  namespace core {
    inline constexpr span_size_type DynamicSpanExtent = (span_size_type)-1;
 
    template <typename T, span_size_type Extent = DynamicSpanExtent>
    class span;
 
    namespace detail {
      template <typename T, span_size_type Extent>
      struct span_storage {
        constexpr span_storage() noexcept = default;
        constexpr span_storage(const span_storage&) noexcept = default;
        constexpr span_storage(span_storage&&) noexcept = default;
        constexpr span_storage& operator=(const span_storage&) noexcept = default;
        constexpr span_storage& operator=(span_storage&&) noexcept = default;
        constexpr span_storage(T* ptr_, span_size_type /*unused*/) noexcept: beg(ptr_), end(ptr_ + Extent) {}
        ~span_storage() noexcept = default;
 
        T* beg = nullptr;
        T* end = nullptr;
        static constexpr span_size_type size = Extent;
      };
 
      template <typename T>
      struct span_storage<T, DynamicSpanExtent> {
        constexpr span_storage() noexcept = default;
        constexpr span_storage(const span_storage&) noexcept = default;
        constexpr span_storage(span_storage&&) noexcept = default;
        constexpr span_storage& operator=(const span_storage&) noexcept = default;
        constexpr span_storage& operator=(span_storage&&) noexcept = default;
        constexpr span_storage(T* ptr_, span_size_type size_) noexcept: beg(ptr_), end(ptr_ + size_) {}
        ~span_storage() noexcept = default;
 
        T* beg = nullptr;
        T* end = nullptr;
      };
 
      template <typename>
      struct is_span: std::false_type {};
 
      template <typename T, span_size_type S>
      struct is_span<span<T, S>>: std::true_type {};
 
      template <typename>
      struct is_std_array: std::false_type {};
 
      template <typename T, auto N>
      struct is_std_array<gaia::cnt::sarray<T, N>>: std::true_type {};
 
      template <typename C, typename U = raw_t<C>>
      struct is_container {
        static constexpr bool value =
            !is_span<U>::value && !is_std_array<U>::value && !std::is_array<U>::value && has_data_size<C>::value;
      };
 
      template <typename, typename, typename = void>
      struct is_container_element_kind_compatible: std::false_type {};
 
      template <typename T, typename E>
      struct is_container_element_kind_compatible<
          T, E,
          typename std::enable_if<
              !std::is_same<typename std::remove_cv<decltype(detail::data(std::declval<T>()))>::type, void>::value &&
              std::is_convertible<
                  typename std::remove_pointer_t<decltype(detail::data(std::declval<T>()))> (*)[],
                  E (*)[]>::value>::type>: std::true_type {};
    } // namespace detail
 
    template <typename T, span_size_type Extent>
    class span {
      static_assert(
          std::is_object<T>::value, "A span's T must be an object type (not a "
                                    "reference type or void)");
      static_assert(
          detail::is_complete<T>::value, "A span's T must be a complete type (not a forward "
                                         "declaration)");
      static_assert(!std::is_abstract<T>::value, "A span's T cannot be an abstract class type");
 
      using m_datatype = detail::span_storage<T, Extent>;
 
    public:
      using element_kind = T;
      using value_type = typename std::remove_cv<T>::type;
      using size_type = span_size_type;
      using difference_type = span_diff_type;
      using pointer = element_kind*;
      using const_pointer = const element_kind*;
      using reference = element_kind&;
      using const_reference = const element_kind&;
 
      using iterator = pointer;
      using const_iterator = const_pointer;
      using iterator_type = core::random_access_iterator_tag;
 
      static constexpr size_type extent = Extent;
 
    private:
      m_datatype m_data{};
 
    public:
      template <span_size_type E = Extent, typename std::enable_if<(E == DynamicSpanExtent || E <= 0), int>::type = 0>
      constexpr span() noexcept {}
 
      constexpr span(pointer ptr, size_type count): m_data(ptr, count) {
        GAIA_ASSERT(extent == DynamicSpanExtent || extent == count);
      }
 
      constexpr span(pointer begin, pointer end): m_data(begin, end - begin) {
        GAIA_ASSERT(extent == DynamicSpanExtent || ((uintptr_t)(end - begin) == (uintptr_t)extent));
      }
 
      template <
          span_size_type N, span_size_type E = Extent,
          typename std::enable_if<
              (E == DynamicSpanExtent || N == E) &&
                  detail::is_container_element_kind_compatible<element_kind (&)[N], T>::value,
              int>::type = 0>
      constexpr span(element_kind (&arr)[N]) noexcept: m_data(arr, N) {}
 
      template <
          typename Container, span_size_type E = Extent,
          typename std::enable_if<
              E == DynamicSpanExtent && detail::is_container<Container>::value &&
                  detail::is_container_element_kind_compatible<Container&, T>::value,
              int>::type = 0>
      constexpr span(Container& cont): m_data(detail::data(cont), detail::size(cont)) {}
 
      template <
          typename Container, span_size_type E = Extent,
          typename std::enable_if<
              E == DynamicSpanExtent && detail::is_container<Container>::value &&
                  detail::is_container_element_kind_compatible<const Container&, T>::value,
              int>::type = 0>
      constexpr span(const Container& cont): m_data(detail::data(cont), detail::size(cont)) {}
 
      constexpr span(const span& other) noexcept = default;
      constexpr span& operator=(const span& other) noexcept = default;
 
      template <
          typename T2, span_size_type Extent2,
          typename std::enable_if<
              (Extent == DynamicSpanExtent || Extent2 == DynamicSpanExtent || Extent == Extent2) &&
                  std::is_convertible<T2 (*)[], T (*)[]>::value,
              int>::type = 0>
      constexpr span(const span<T2, Extent2>& other) noexcept: m_data(other.data(), other.size()) {}
 
      ~span() noexcept = default;
 
      GAIA_NODISCARD constexpr pointer data() const noexcept {
        return m_data.beg;
      }
 
      GAIA_NODISCARD constexpr size_type size() const noexcept {
        return size_type(m_data.end - m_data.beg);
      }
 
      GAIA_NODISCARD constexpr bool empty() const noexcept {
        return m_data.beg == m_data.end;
      }
 
      GAIA_NODISCARD constexpr reference operator[](size_type index) const {
        GAIA_ASSERT((uintptr_t)m_data.beg + index < (uintptr_t)m_data.end);
        return *(m_data.beg + index);
      }
 
      GAIA_NODISCARD constexpr iterator begin() noexcept {
        return {m_data.beg};
      }
 
      GAIA_NODISCARD constexpr iterator begin() const noexcept {
        return {m_data.beg};
      }
 
      GAIA_NODISCARD constexpr const_iterator cbegin() const noexcept {
        return {m_data.beg};
      }
 
      GAIA_NODISCARD constexpr iterator end() noexcept {
        return {m_data.end};
      }
 
      GAIA_NODISCARD constexpr const_iterator end() const noexcept {
        return {m_data.end};
      }
 
      GAIA_NODISCARD constexpr const_iterator cend() const noexcept {
        return {m_data.end};
      }
 
      template <span_size_type Count>
      GAIA_NODISCARD constexpr span<element_kind, Count> first() const {
        GAIA_ASSERT(Count <= size());
        return {m_data.beg, Count};
      }
 
      GAIA_NODISCARD constexpr span<element_kind, DynamicSpanExtent> first(size_type count) const {
        GAIA_ASSERT(count <= size());
        return {m_data.beg, count};
      }
 
      template <span_size_type Count>
      GAIA_NODISCARD constexpr span<element_kind, Count> last() const {
        GAIA_ASSERT(Count <= size());
        return {m_data.beg + (size() - Count), Count};
      }
 
      GAIA_NODISCARD constexpr span<element_kind, DynamicSpanExtent> last(size_type count) const {
        GAIA_ASSERT(count <= size());
        return {m_data.beg + (size() - count), count};
      }
 
      GAIA_NODISCARD constexpr reference front() const {
        GAIA_ASSERT(!empty());
        return *m_data.beg;
      }
 
      GAIA_NODISCARD constexpr reference back() const {
        GAIA_ASSERT(!empty());
        return *(m_data.beg + (size() - 1));
      }
 
      template <span_size_type Offset, span_size_type Count = DynamicSpanExtent>
      using subspan_return_t = span<
          T, Count != DynamicSpanExtent ? Count : (Extent != DynamicSpanExtent ? Extent - Offset : DynamicSpanExtent)>;
 
      template <span_size_type Offset, span_size_type Count = DynamicSpanExtent>
      GAIA_NODISCARD constexpr subspan_return_t<Offset, Count> subspan() const {
        GAIA_ASSERT(Offset <= size() && (Count == DynamicSpanExtent || Offset + Count <= size()));
        return {m_data.beg + Offset, Count != DynamicSpanExtent ? Count : size() - Offset};
      }
 
      GAIA_NODISCARD constexpr span<element_kind, DynamicSpanExtent>
      subspan(size_type offset, size_type count = DynamicSpanExtent) const {
        GAIA_ASSERT(offset <= size() && (count == DynamicSpanExtent || offset + count <= size()));
        return {m_data.beg + offset, count != DynamicSpanExtent ? count : size() - offset};
      }
    };
 
    template <typename T, size_t N>
    span(T (&)[N]) -> span<T, N>;
 
    template <typename T, size_t N>
    span(gaia::cnt::sarray<T, N>&) -> span<T, N>;
 
    template <typename T, size_t N>
    span(const gaia::cnt::sarray<T, N>&) -> span<const T, N>;
 
    template <typename Container>
    span(Container&) -> span<typename std::remove_reference<decltype(*detail::data(std::declval<Container&>()))>::type>;
 
    template <typename Container>
    span(const Container&) -> span<const typename Container::value_type>;
 
    template <span_size_type N, typename E, span_size_type S>
    constexpr auto get(span<E, S> s) -> decltype(s[N]) {
      return s[N];
    }
  } // namespace core
} // namespace gaia
 
namespace std {
  template <typename T, size_t Extent>
  struct tuple_size<gaia::core::span<T, Extent>>: public integral_constant<size_t, Extent> {};
 
  template <typename T>
  struct tuple_size<gaia::core::span<T, gaia::core::DynamicSpanExtent>>; // not defined
 
  template <size_t I, typename T, size_t Extent>
  struct tuple_element<I, gaia::core::span<T, Extent>> {
    static_assert(Extent != gaia::core::DynamicSpanExtent && I < Extent, "");
    using type = T;
  };
} // end namespace std