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Add back port of std::span (open-telemetry#21)
* Start filling out span backport * Fix assertion * Add a span test. * Fix constructors * Fill out span tests * Add test coverage for pointer-count construction * s/ASSERT_DEATH/EXPECT_DEATH/ * Add bracket operator test * Add test coverage for other span construction. * Add test coverage for array construction * Add test for range construction * Fix typo. * Add assignment test * Add iteration test * Add data/size functions * Add array overloads * Support implicit construction from general containers * Reformat * Fix typo * Fix typo * Fix enable_if condition
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‎api/include/opentelemetry/nostd/span.h

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#pragma once
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#include <array>
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#include <cassert>
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#include <cstddef>
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#include <exception>
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#include <iterator>
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#include <type_traits>
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#include "opentelemetry/nostd/utility.h"
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namespace opentelemetry
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{
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namespace nostd
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{
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constexpr size_t dynamic_extent = static_cast<size_t>(-1);
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template <class T, size_t Extent = dynamic_extent>
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class span;
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namespace detail
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{
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/**
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* Helper class to resolve overloaded constructors
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*/
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template <class T>
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struct is_specialized_span_convertible : std::false_type
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{};
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template <class T, size_t N>
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struct is_specialized_span_convertible<std::array<T, N>> : std::true_type
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{};
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template <class T, size_t N>
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struct is_specialized_span_convertible<T[N]> : std::true_type
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{};
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template <class T, size_t Extent>
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struct is_specialized_span_convertible<span<T, Extent>> : std::true_type
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{};
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} // namespace detail
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/**
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* Back port of std::span.
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*
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* See https://en.cppreference.com/w/cpp/container/span for interface documentation.
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*
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* Note: This provides a subset of the methods available on std::span.
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*
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* Note: The std::span API specifies error cases to have undefined behavior, so this implementation
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* chooses to terminate or assert rather than throw exceptions.
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*/
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template <class T, size_t Extent>
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class span
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{
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public:
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static constexpr size_t extent = Extent;
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// This arcane code is how we make default-construction result in an SFINAE error
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// with C++11 when Extent != 0 as specified by the std::span API.
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//
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// See https://stackoverflow.com/a/10309720/4447365
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template <bool B = Extent == 0, typename std::enable_if<B>::type * = nullptr>
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span() noexcept : data_{nullptr}
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{}
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span(T *data, size_t count) noexcept : data_{data}
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{
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if (count != Extent)
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{
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std::terminate();
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}
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}
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span(T *first, T *last) noexcept : data_{first}
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{
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if (std::distance(first, last) != Extent)
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{
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std::terminate();
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}
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}
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template <size_t N, typename std::enable_if<Extent == N>::type * = nullptr>
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span(T (&array)[N]) noexcept : data_{array}
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{}
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template <size_t N, typename std::enable_if<Extent == N>::type * = nullptr>
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span(std::array<T, N> &array) noexcept : data_{array.data()}
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{}
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template <size_t N, typename std::enable_if<Extent == N>::type * = nullptr>
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span(const std::array<T, N> &array) noexcept : data_{array.data()}
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{}
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template <
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class C,
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typename std::enable_if<!detail::is_specialized_span_convertible<C>::value &&
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std::is_convertible<typename std::remove_pointer<decltype(nostd::data(
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std::declval<C &>()))>::type (*)[],
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T (*)[]>::value &&
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std::is_convertible<decltype(nostd::size(std::declval<const C &>())),
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size_t>::value>::type * = nullptr>
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span(C &c) noexcept(noexcept(nostd::data(c), nostd::size(c))) : data_{nostd::data(c)}
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{
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if (nostd::size(c) != Extent)
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{
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std::terminate();
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}
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}
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template <
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class C,
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typename std::enable_if<!detail::is_specialized_span_convertible<C>::value &&
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std::is_convertible<typename std::remove_pointer<decltype(nostd::data(
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std::declval<const C &>()))>::type (*)[],
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T (*)[]>::value &&
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std::is_convertible<decltype(nostd::size(std::declval<const C &>())),
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size_t>::value>::type * = nullptr>
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span(const C &c) noexcept(noexcept(nostd::data(c), nostd::size(c))) : data_{nostd::data(c)}
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{
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if (nostd::size(c) != Extent)
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{
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std::terminate();
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}
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}
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template <class U,
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size_t N,
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typename std::enable_if<N == Extent &&
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std::is_convertible<U (*)[], T (*)[]>::value>::type * = nullptr>
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span(const span<U, N> &other) noexcept : data_{other.data()}
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{}
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span(const span &) noexcept = default;
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bool empty() const noexcept { return Extent == 0; }
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T *data() const noexcept { return data_; }
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size_t size() const noexcept { return Extent; }
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T &operator[](size_t index) const noexcept
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{
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assert(index < Extent);
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return data_[index];
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}
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T *begin() const noexcept { return data_; }
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T *end() const noexcept { return data_ + Extent; }
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private:
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T *data_;
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};
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template <class T>
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class span<T, dynamic_extent>
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{
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public:
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static constexpr size_t extent = dynamic_extent;
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span() noexcept : extent_{0}, data_{nullptr} {}
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span(T *data, size_t count) noexcept : extent_{count}, data_{data} {}
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span(T *first, T *last) noexcept
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: extent_{static_cast<size_t>(std::distance(first, last))}, data_{first}
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{
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assert(first <= last);
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}
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template <size_t N>
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span(T (&array)[N]) noexcept : extent_{N}, data_{array}
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{}
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template <size_t N>
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span(std::array<T, N> &array) noexcept : extent_{N}, data_{array.data()}
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{}
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template <size_t N>
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span(const std::array<T, N> &array) noexcept : extent_{N}, data_{array.data()}
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{}
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template <
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class C,
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typename std::enable_if<!detail::is_specialized_span_convertible<C>::value &&
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std::is_convertible<typename std::remove_pointer<decltype(nostd::data(
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std::declval<C &>()))>::type (*)[],
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T (*)[]>::value &&
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std::is_convertible<decltype(nostd::size(std::declval<const C &>())),
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size_t>::value>::type * = nullptr>
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span(C &c) noexcept(noexcept(nostd::data(c), nostd::size(c)))
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: extent_{nostd::size(c)}, data_{nostd::data(c)}
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{}
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template <
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class C,
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typename std::enable_if<!detail::is_specialized_span_convertible<C>::value &&
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std::is_convertible<typename std::remove_pointer<decltype(nostd::data(
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std::declval<const C &>()))>::type (*)[],
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T (*)[]>::value &&
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std::is_convertible<decltype(nostd::size(std::declval<const C &>())),
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size_t>::value>::type * = nullptr>
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span(const C &c) noexcept(noexcept(nostd::data(c), nostd::size(c)))
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: extent_{nostd::size(c)}, data_{nostd::data(c)}
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{}
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template <class U,
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size_t N,
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typename std::enable_if<std::is_convertible<U (*)[], T (*)[]>::value>::type * = nullptr>
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span(const span<U, N> &other) noexcept : extent_{other.size()}, data_{other.data()}
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{}
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span(const span &) noexcept = default;
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bool empty() const noexcept { return extent_ == 0; }
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T *data() const noexcept { return data_; }
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size_t size() const noexcept { return extent_; }
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T &operator[](size_t index) const noexcept
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{
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assert(index < extent_);
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return data_[index];
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}
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T *begin() const noexcept { return data_; }
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T *end() const noexcept { return data_ + extent_; }
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private:
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// Note: matches libstdc++'s layout for std::span
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// See
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// https://github.com/gcc-mirror/gcc/blob/a60701e05b3878000ff9fdde1aecbc472b9dec5a/libstdc%2B%2B-v3/include/std/span#L402-L403
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size_t extent_;
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T *data_;
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};
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} // namespace nostd
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} // namespace opentelemetry

‎api/include/opentelemetry/nostd/utility.h

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#pragma once
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#include <cstddef>
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#include <initializer_list>
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namespace opentelemetry
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{
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namespace nostd
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{
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/**
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* Back port of std::data
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*
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* See https://en.cppreference.com/w/cpp/iterator/data
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*/
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template <class C>
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auto data(C &c) noexcept(noexcept(c.data())) -> decltype(c.data())
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{
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return c.data();
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}
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template <class C>
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auto data(const C &c) noexcept(noexcept(c.data())) -> decltype(c.data())
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{
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return c.data();
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}
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template <class T, size_t N>
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T *data(T (&array)[N]) noexcept
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{
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return array;
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}
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template <class E>
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const E *data(std::initializer_list<E> list) noexcept
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{
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return list.begin();
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}
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/**
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* Back port of std::size
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*
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* See https://en.cppreference.com/w/cpp/iterator/size
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*/
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template <class C>
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auto size(const C &c) noexcept(noexcept(c.size())) -> decltype(c.size())
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{
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return c.size();
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}
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template <class T, size_t N>
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size_t size(T (&array)[N]) noexcept
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{
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return N;
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}
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} // namespace nostd
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} // namespace opentelemetry

‎api/test/nostd/BUILD

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"@com_google_googletest//:gtest_main",
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],
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)
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cc_test(
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name = "utility_test",
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srcs = [
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"utility_test.cc",
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],
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deps = [
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"//api",
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"@com_google_googletest//:gtest_main",
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],
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)
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cc_test(
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name = "span_test",
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srcs = [
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"span_test.cc",
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],
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deps = [
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"//api",
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"@com_google_googletest//:gtest_main",
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],
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)

‎api/test/nostd/CMakeLists.txt

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${CMAKE_THREAD_LIBS_INIT} opentelemetry_api)
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gtest_add_tests(TARGET string_view_test TEST_PREFIX nostd. TEST_LIST
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string_view_test)
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add_executable(utility_test utility_test.cc)
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target_link_libraries(utility_test ${GTEST_BOTH_LIBRARIES}
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${CMAKE_THREAD_LIBS_INIT} opentelemetry_api)
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gtest_add_tests(TARGET utility_test TEST_PREFIX nostd. TEST_LIST utility_test)
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add_executable(span_test span_test.cc)
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target_link_libraries(span_test ${GTEST_BOTH_LIBRARIES}
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${CMAKE_THREAD_LIBS_INIT} opentelemetry_api)
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gtest_add_tests(TARGET span_test TEST_PREFIX nostd. TEST_LIST span_test)

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