span.hh

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#ifndef WASMTIME_SPAN_HH
#define WASMTIME_SPAN_HH
 
#ifdef __has_include
#if __has_include(<span>)
#include <span>
#endif
#endif
 
#ifndef __cpp_lib_span
#include <cstddef>
#include <limits>
#include <type_traits>
#endif
 
namespace wasmtime {
 
#ifdef __cpp_lib_span
 
template <typename T, std::size_t Extent = std::dynamic_extent>
using Span = std::span<T, Extent>;
 
#else
 
inline constexpr size_t dynamic_extent =
    std::numeric_limits<std::size_t>::max();
 
template <typename T, std::size_t Extent = dynamic_extent> class Span;
 
template <typename T> struct IsSpan : std::false_type {};
 
template <typename T, std::size_t Extent>
struct IsSpan<Span<T, Extent>> : std::true_type {};
 
template <typename T, std::size_t Extent> class Span {
  static_assert(Extent == dynamic_extent,
                "The current implementation supports dynamic-extent span only");
 
public:
  using iterator = T *;
 
  Span(T *t, std::size_t n) : ptr_{t}, size_{n} {}
 
  template <typename C,
            std::enable_if_t<
                !IsSpan<C>::value &&
                    std::is_pointer_v<decltype(std::declval<C &>().data())> &&
                    std::is_convertible_v<
                        std::remove_pointer_t<
                            decltype(std::declval<C &>().data())> (*)[],
                        T (*)[]> &&
                    std::is_convertible_v<decltype(std::declval<C>().size()),
                                          std::size_t>,
                int> = 0>
  Span(C &range) : ptr_{range.data()}, size_{range.size()} {}
 
  T &operator[](ptrdiff_t idx) const {
    return ptr_[idx]; // NOLINT
  }
 
  T *data() const { return ptr_; }
 
  std::size_t size() const { return size_; }
 
  iterator begin() const { return ptr_; }
 
  iterator end() const {
    return ptr_ + size_; // NOLINT
  }
 
  std::size_t size_bytes() const { return sizeof(T) * size_; }
 
private:
  T *ptr_;
  std::size_t size_;
};
 
#endif
 
} // namespace wasmtime
 
#endif // WASMTIME_SPAN_HH