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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
#pragma once
// Try to use either `std::span` or `gsl::span`
#if defined(OPENTELEMETRY_STL_VERSION)
# if OPENTELEMETRY_STL_VERSION >= 2020
# include <array>
# include <cstddef>
# include <iterator>
# include <type_traits>
/**
* @brief Clang 14.0.0 with libc++ do not support implicitly construct a span
* for a range. We just use our fallback version.
*
*/
# if !defined(OPENTELEMETRY_OPTION_USE_STD_SPAN) && defined(_LIBCPP_VERSION)
# if _LIBCPP_VERSION <= 14000
# define OPENTELEMETRY_OPTION_USE_STD_SPAN 0
# endif
# endif
# ifndef OPENTELEMETRY_OPTION_USE_STD_SPAN
# define OPENTELEMETRY_OPTION_USE_STD_SPAN 1
# endif
# if OPENTELEMETRY_OPTION_USE_STD_SPAN
# include "opentelemetry/std/span.h"
# endif
# endif /* OPENTELEMETRY_STL_VERSION >= 2020 */
#endif /* OPENTELEMETRY_STL_VERSION */
// Fallback to `nostd::span` if necessary
#if !defined(OPENTELEMETRY_HAVE_SPAN)
# include <array>
# include <cassert>
# include <cstddef>
# include <exception>
# include <iterator>
# include <type_traits>
# include "opentelemetry/nostd/utility.h"
# include "opentelemetry/version.h"
OPENTELEMETRY_BEGIN_NAMESPACE
namespace nostd
{
constexpr size_t dynamic_extent = static_cast<size_t>(-1);
template <class T, size_t Extent = dynamic_extent>
class span;
namespace detail
{
/**
* Helper class to resolve overloaded constructors
*/
template <class T>
struct is_specialized_span_convertible : std::false_type
{};
template <class T, size_t N>
struct is_specialized_span_convertible<std::array<T, N>> : std::true_type
{};
template <class T, size_t N>
struct is_specialized_span_convertible<T[N]> : std::true_type
{};
template <class T, size_t Extent>
struct is_specialized_span_convertible<span<T, Extent>> : std::true_type
{};
} // namespace detail
/**
* Back port of std::span.
*
*
* Note: This provides a subset of the methods available on std::span.
*
* Note: The std::span API specifies error cases to have undefined behavior, so this implementation
* chooses to terminate or assert rather than throw exceptions.
*/
template <class T, size_t Extent>
class span
{
public:
static constexpr size_t extent = Extent;
// This arcane code is how we make default-construction result in an SFINAE error
// with C++11 when Extent != 0 as specified by the std::span API.
//
template <bool B = Extent == 0, typename std::enable_if<B>::type * = nullptr>
span() noexcept : data_{nullptr}
{}
span(T *data, size_t count) noexcept : data_{data}
{
if (count != Extent)
{
std::terminate();
}
}
span(T *first, T *last) noexcept : data_{first}
{
if (std::distance(first, last) != Extent)
{
std::terminate();
}
}
template <size_t N, typename std::enable_if<Extent == N>::type * = nullptr>
span(T (&array)[N]) noexcept : data_{array}
{}
template <size_t N, typename std::enable_if<Extent == N>::type * = nullptr>
span(std::array<T, N> &array) noexcept : data_{array.data()}
{}
template <size_t N, typename std::enable_if<Extent == N>::type * = nullptr>
span(const std::array<T, N> &array) noexcept : data_{array.data()}
{}
template <
class C,
typename std::enable_if<!detail::is_specialized_span_convertible<C>::value &&
std::is_convertible<typename std::remove_pointer<decltype(nostd::data(
std::declval<C &>()))>::type (*)[],
T (*)[]>::value &&
std::is_convertible<decltype(nostd::size(std::declval<const C &>())),
size_t>::value>::type * = nullptr>
span(C &c) noexcept(noexcept(nostd::data(c), nostd::size(c))) : data_{nostd::data(c)}
{
if (nostd::size(c) != Extent)
{
std::terminate();
}
}
template <
class C,
typename std::enable_if<!detail::is_specialized_span_convertible<C>::value &&
std::is_convertible<typename std::remove_pointer<decltype(nostd::data(
std::declval<const C &>()))>::type (*)[],
T (*)[]>::value &&
std::is_convertible<decltype(nostd::size(std::declval<const C &>())),
size_t>::value>::type * = nullptr>
span(const C &c) noexcept(noexcept(nostd::data(c), nostd::size(c))) : data_{nostd::data(c)}
{
if (nostd::size(c) != Extent)
{
std::terminate();
}
}
template <class U,
size_t N,
typename std::enable_if<N == Extent &&
std::is_convertible<U (*)[], T (*)[]>::value>::type * = nullptr>
span(const span<U, N> &other) noexcept : data_{other.data()}
{}
span(const span &) noexcept = default;
span &operator=(const span &) noexcept = default;
bool empty() const noexcept { return Extent == 0; }
T *data() const noexcept { return data_; }
size_t size() const noexcept { return Extent; }
T &operator[](size_t index) const noexcept
{
assert(index < Extent);
return data_[index];
}
T *begin() const noexcept { return data_; }
T *end() const noexcept { return data_ + Extent; }
private:
T *data_;
};
template <class T>
class span<T, dynamic_extent>
{
public:
static constexpr size_t extent = dynamic_extent;
span() noexcept : extent_{0}, data_{nullptr} {}
span(T *data, size_t count) noexcept : extent_{count}, data_{data} {}
span(T *first, T *last) noexcept
: extent_{static_cast<size_t>(std::distance(first, last))}, data_{first}
{
assert(first <= last);
}
template <size_t N>
span(T (&array)[N]) noexcept : extent_{N}, data_{array}
{}
template <size_t N>
span(std::array<T, N> &array) noexcept : extent_{N}, data_{array.data()}
{}
template <size_t N>
span(const std::array<T, N> &array) noexcept : extent_{N}, data_{array.data()}
{}
template <
class C,
typename std::enable_if<!detail::is_specialized_span_convertible<C>::value &&
std::is_convertible<typename std::remove_pointer<decltype(nostd::data(
std::declval<C &>()))>::type (*)[],
T (*)[]>::value &&
std::is_convertible<decltype(nostd::size(std::declval<const C &>())),
size_t>::value>::type * = nullptr>
span(C &c) noexcept(noexcept(nostd::data(c), nostd::size(c)))
: extent_{nostd::size(c)}, data_{nostd::data(c)}
{}
template <
class C,
typename std::enable_if<!detail::is_specialized_span_convertible<C>::value &&
std::is_convertible<typename std::remove_pointer<decltype(nostd::data(
std::declval<const C &>()))>::type (*)[],
T (*)[]>::value &&
std::is_convertible<decltype(nostd::size(std::declval<const C &>())),
size_t>::value>::type * = nullptr>
span(const C &c) noexcept(noexcept(nostd::data(c), nostd::size(c)))
: extent_{nostd::size(c)}, data_{nostd::data(c)}
{}
template <class U,
size_t N,
typename std::enable_if<std::is_convertible<U (*)[], T (*)[]>::value>::type * = nullptr>
span(const span<U, N> &other) noexcept : extent_{other.size()}, data_{other.data()}
{}
span(const span &) noexcept = default;
span &operator=(const span &) noexcept = default;
bool empty() const noexcept { return extent_ == 0; }
T *data() const noexcept { return data_; }
size_t size() const noexcept { return extent_; }
T &operator[](size_t index) const noexcept
{
assert(index < extent_);
return data_[index];
}
T *begin() const noexcept { return data_; }
T *end() const noexcept { return data_ + extent_; }
private:
size_t extent_;
T *data_;
};
} // namespace nostd
OPENTELEMETRY_END_NAMESPACE
#endif