ceph/src/jaegertracing/opentelemetry-cpp/api/include/opentelemetry/std/span.h

   1 // Copyright The OpenTelemetry Authors
   2 // SPDX-License-Identifier: Apache-2.0
   3
   4 #pragma once
   5
   6 #include "opentelemetry/version.h"
   7
   8 // Standard library implementation requires at least C++17 compiler.
   9 // Older C++14 compilers may provide support for __has_include as a
  10 // conforming extension.
  11 #if defined __has_include
  12 #  if __has_include(<version>)  // Check for __cpp_{feature}
  13 #    include <version>
  14 #    if defined(__cpp_lib_span) && __cplusplus > 201703L
  15 #      define HAVE_SPAN
  16 #    endif
  17 #  endif
  18 #  if !defined(HAVE_SPAN)
  19 #    // Check for Visual Studio span
  20 #    if defined(_MSVC_LANG) && _HAS_CXX20
  21 #      define HAVE_SPAN
  22 #    endif
  23 #    // Check for other compiler span implementation
  24 #    if !defined(_MSVC_LANG) && __has_include(<span>) && __cplusplus > 201703L
  25 // This works as long as compiler standard is set to C++20
  26 #      define HAVE_SPAN
  27 #    endif
  28 #  endif
  29 #  if !__has_include(<gsl/gsl>)
  30 #    undef HAVE_GSL
  31 #  endif
  32 #endif
  33
  34 #if !defined(HAVE_SPAN)
  35 #  if defined(HAVE_GSL)
  36 #    include <type_traits>
  37 // Guidelines Support Library provides an implementation of std::span
  38 #    include <gsl/gsl>
  39 OPENTELEMETRY_BEGIN_NAMESPACE
  40 namespace nostd
  41 {
  42 using gsl::dynamic_extent;
  43 template <class ElementType, std::size_t Extent = gsl::dynamic_extent>
  44 using span = gsl::span<ElementType, Extent>;
  45 }  // namespace nostd
  46 OPENTELEMETRY_END_NAMESPACE
  47 #    define HAVE_SPAN
  48 #  else
  49 // No `gsl::span`, no `std::span`, fallback to `nostd::span`
  50 #  endif
  51
  52 #else  // HAVE_SPAN
  53 // Using std::span (https://wg21.link/P0122R7) from Standard Library available in C++20 :
  54 // - GCC libstdc++ 10+
  55 // - Clang libc++ 7
  56 // - MSVC Standard Library 19.26*
  57 // - Apple Clang 10.0.0*
  58 #  include <limits>
  59 #  include <span>
  60 OPENTELEMETRY_BEGIN_NAMESPACE
  61 namespace nostd
  62 {
  63 constexpr std::size_t dynamic_extent = (std::numeric_limits<std::size_t>::max());
  64
  65 template <class ElementType, std::size_t Extent = nostd::dynamic_extent>
  66 using span = std::span<ElementType, Extent>;
  67 }  // namespace nostd
  68 OPENTELEMETRY_END_NAMESPACE
  69 #endif  // of HAVE_SPAN