Squashed 'third_party/GSL/' content from commit 0cebbd7
Change-Id: Iffb2e32f2f45297ac6d3e82168cd9df4ac5acc2f
git-subtree-dir: third_party/GSL
git-subtree-split: 0cebbd77bfc21acbf1cc05983ad626539eeeb8e0
diff --git a/include/gsl/span b/include/gsl/span
new file mode 100644
index 0000000..2fa9cc5
--- /dev/null
+++ b/include/gsl/span
@@ -0,0 +1,766 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef GSL_SPAN_H
+#define GSL_SPAN_H
+
+#include <gsl/gsl_assert> // for Expects
+#include <gsl/gsl_byte> // for byte
+#include <gsl/gsl_util> // for narrow_cast, narrow
+
+#include <algorithm> // for lexicographical_compare
+#include <array> // for array
+#include <cstddef> // for ptrdiff_t, size_t, nullptr_t
+#include <iterator> // for reverse_iterator, distance, random_access_...
+#include <limits>
+#include <stdexcept>
+#include <type_traits> // for enable_if_t, declval, is_convertible, inte...
+#include <utility>
+
+#ifdef _MSC_VER
+#pragma warning(push)
+
+// turn off some warnings that are noisy about our Expects statements
+#pragma warning(disable : 4127) // conditional expression is constant
+#pragma warning(disable : 4702) // unreachable code
+
+// blanket turn off warnings from CppCoreCheck for now
+// so people aren't annoyed by them when running the tool.
+// more targeted suppressions will be added in a future update to the GSL
+#pragma warning(disable : 26481 26482 26483 26485 26490 26491 26492 26493 26495)
+
+#if _MSC_VER < 1910
+#pragma push_macro("constexpr")
+#define constexpr /*constexpr*/
+#define GSL_USE_STATIC_CONSTEXPR_WORKAROUND
+
+#endif // _MSC_VER < 1910
+#else // _MSC_VER
+
+// See if we have enough C++17 power to use a static constexpr data member
+// without needing an out-of-line definition
+#if !(defined(__cplusplus) && (__cplusplus >= 201703L))
+#define GSL_USE_STATIC_CONSTEXPR_WORKAROUND
+#endif // !(defined(__cplusplus) && (__cplusplus >= 201703L))
+
+#endif // _MSC_VER
+
+// GCC 7 does not like the signed unsigned missmatch (size_t ptrdiff_t)
+// While there is a conversion from signed to unsigned, it happens at
+// compiletime, so the compiler wouldn't have to warn indiscriminently, but
+// could check if the source value actually doesn't fit into the target type
+// and only warn in those cases.
+#if __GNUC__ > 6
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
+
+namespace gsl
+{
+
+// [views.constants], constants
+constexpr const std::ptrdiff_t dynamic_extent = -1;
+
+template <class ElementType, std::ptrdiff_t Extent = dynamic_extent>
+class span;
+
+// implementation details
+namespace details
+{
+ template <class T>
+ struct is_span_oracle : std::false_type
+ {
+ };
+
+ template <class ElementType, std::ptrdiff_t Extent>
+ struct is_span_oracle<gsl::span<ElementType, Extent>> : std::true_type
+ {
+ };
+
+ template <class T>
+ struct is_span : public is_span_oracle<std::remove_cv_t<T>>
+ {
+ };
+
+ template <class T>
+ struct is_std_array_oracle : std::false_type
+ {
+ };
+
+ template <class ElementType, std::size_t Extent>
+ struct is_std_array_oracle<std::array<ElementType, Extent>> : std::true_type
+ {
+ };
+
+ template <class T>
+ struct is_std_array : public is_std_array_oracle<std::remove_cv_t<T>>
+ {
+ };
+
+ template <std::ptrdiff_t From, std::ptrdiff_t To>
+ struct is_allowed_extent_conversion
+ : public std::integral_constant<bool, From == To || From == gsl::dynamic_extent ||
+ To == gsl::dynamic_extent>
+ {
+ };
+
+ template <class From, class To>
+ struct is_allowed_element_type_conversion
+ : public std::integral_constant<bool, std::is_convertible<From (*)[], To (*)[]>::value>
+ {
+ };
+
+ template <class Span, bool IsConst>
+ class span_iterator
+ {
+ using element_type_ = typename Span::element_type;
+
+ public:
+
+#ifdef _MSC_VER
+ // Tell Microsoft standard library that span_iterators are checked.
+ using _Unchecked_type = typename Span::pointer;
+#endif
+
+ using iterator_category = std::random_access_iterator_tag;
+ using value_type = std::remove_cv_t<element_type_>;
+ using difference_type = typename Span::index_type;
+
+ using reference = std::conditional_t<IsConst, const element_type_, element_type_>&;
+ using pointer = std::add_pointer_t<reference>;
+
+ span_iterator() = default;
+
+ constexpr span_iterator(const Span* span, typename Span::index_type idx) noexcept
+ : span_(span), index_(idx)
+ {}
+
+ friend span_iterator<Span, true>;
+ template<bool B, std::enable_if_t<!B && IsConst>* = nullptr>
+ constexpr span_iterator(const span_iterator<Span, B>& other) noexcept
+ : span_iterator(other.span_, other.index_)
+ {
+ }
+
+ constexpr reference operator*() const
+ {
+ Expects(index_ != span_->size());
+ return *(span_->data() + index_);
+ }
+
+ constexpr pointer operator->() const
+ {
+ Expects(index_ != span_->size());
+ return span_->data() + index_;
+ }
+
+ constexpr span_iterator& operator++()
+ {
+ Expects(0 <= index_ && index_ != span_->size());
+ ++index_;
+ return *this;
+ }
+
+ constexpr span_iterator operator++(int)
+ {
+ auto ret = *this;
+ ++(*this);
+ return ret;
+ }
+
+ constexpr span_iterator& operator--()
+ {
+ Expects(index_ != 0 && index_ <= span_->size());
+ --index_;
+ return *this;
+ }
+
+ constexpr span_iterator operator--(int)
+ {
+ auto ret = *this;
+ --(*this);
+ return ret;
+ }
+
+ constexpr span_iterator operator+(difference_type n) const
+ {
+ auto ret = *this;
+ return ret += n;
+ }
+
+ friend constexpr span_iterator operator+(difference_type n, span_iterator const& rhs)
+ {
+ return rhs + n;
+ }
+
+ constexpr span_iterator& operator+=(difference_type n)
+ {
+ Expects((index_ + n) >= 0 && (index_ + n) <= span_->size());
+ index_ += n;
+ return *this;
+ }
+
+ constexpr span_iterator operator-(difference_type n) const
+ {
+ auto ret = *this;
+ return ret -= n;
+ }
+
+ constexpr span_iterator& operator-=(difference_type n) { return *this += -n; }
+
+ constexpr difference_type operator-(span_iterator rhs) const
+ {
+ Expects(span_ == rhs.span_);
+ return index_ - rhs.index_;
+ }
+
+ constexpr reference operator[](difference_type n) const
+ {
+ return *(*this + n);
+ }
+
+ constexpr friend bool operator==(span_iterator lhs,
+ span_iterator rhs) noexcept
+ {
+ return lhs.span_ == rhs.span_ && lhs.index_ == rhs.index_;
+ }
+
+ constexpr friend bool operator!=(span_iterator lhs,
+ span_iterator rhs) noexcept
+ {
+ return !(lhs == rhs);
+ }
+
+ constexpr friend bool operator<(span_iterator lhs,
+ span_iterator rhs) noexcept
+ {
+ return lhs.index_ < rhs.index_;
+ }
+
+ constexpr friend bool operator<=(span_iterator lhs,
+ span_iterator rhs) noexcept
+ {
+ return !(rhs < lhs);
+ }
+
+ constexpr friend bool operator>(span_iterator lhs,
+ span_iterator rhs) noexcept
+ {
+ return rhs < lhs;
+ }
+
+ constexpr friend bool operator>=(span_iterator lhs,
+ span_iterator rhs) noexcept
+ {
+ return !(rhs > lhs);
+ }
+
+#ifdef _MSC_VER
+ // MSVC++ iterator debugging support; allows STL algorithms in 15.8+
+ // to unwrap span_iterator to a pointer type after a range check in STL
+ // algorithm calls
+ friend constexpr void _Verify_range(span_iterator lhs,
+ span_iterator rhs) noexcept
+ { // test that [lhs, rhs) forms a valid range inside an STL algorithm
+ Expects(lhs.span_ == rhs.span_ // range spans have to match
+ && lhs.index_ <= rhs.index_); // range must not be transposed
+ }
+
+ constexpr void _Verify_offset(const difference_type n) const noexcept
+ { // test that the iterator *this + n is a valid range in an STL
+ // algorithm call
+ Expects((index_ + n) >= 0 && (index_ + n) <= span_->size());
+ }
+
+ constexpr pointer _Unwrapped() const noexcept
+ { // after seeking *this to a high water mark, or using one of the
+ // _Verify_xxx functions above, unwrap this span_iterator to a raw
+ // pointer
+ return span_->data() + index_;
+ }
+
+ // Tell the STL that span_iterator should not be unwrapped if it can't
+ // validate in advance, even in release / optimized builds:
+#if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
+ static constexpr const bool _Unwrap_when_unverified = false;
+#else
+ static constexpr bool _Unwrap_when_unverified = false;
+#endif
+ constexpr void _Seek_to(const pointer p) noexcept
+ { // adjust the position of *this to previously verified location p
+ // after _Unwrapped
+ index_ = p - span_->data();
+ }
+#endif
+
+ protected:
+ const Span* span_ = nullptr;
+ std::ptrdiff_t index_ = 0;
+ };
+
+ template <std::ptrdiff_t Ext>
+ class extent_type
+ {
+ public:
+ using index_type = std::ptrdiff_t;
+
+ static_assert(Ext >= 0, "A fixed-size span must be >= 0 in size.");
+
+ constexpr extent_type() noexcept {}
+
+ template <index_type Other>
+ constexpr extent_type(extent_type<Other> ext)
+ {
+ static_assert(Other == Ext || Other == dynamic_extent,
+ "Mismatch between fixed-size extent and size of initializing data.");
+ Expects(ext.size() == Ext);
+ }
+
+ constexpr extent_type(index_type size) { Expects(size == Ext); }
+
+ constexpr index_type size() const noexcept { return Ext; }
+ };
+
+ template <>
+ class extent_type<dynamic_extent>
+ {
+ public:
+ using index_type = std::ptrdiff_t;
+
+ template <index_type Other>
+ explicit constexpr extent_type(extent_type<Other> ext) : size_(ext.size())
+ {
+ }
+
+ explicit constexpr extent_type(index_type size) : size_(size) { Expects(size >= 0); }
+
+ constexpr index_type size() const noexcept { return size_; }
+
+ private:
+ index_type size_;
+ };
+
+ template <class ElementType, std::ptrdiff_t Extent, std::ptrdiff_t Offset, std::ptrdiff_t Count>
+ struct calculate_subspan_type
+ {
+ using type = span<ElementType, Count != dynamic_extent ? Count : (Extent != dynamic_extent ? Extent - Offset : Extent)>;
+ };
+} // namespace details
+
+// [span], class template span
+template <class ElementType, std::ptrdiff_t Extent>
+class span
+{
+public:
+ // constants and types
+ using element_type = ElementType;
+ using value_type = std::remove_cv_t<ElementType>;
+ using index_type = std::ptrdiff_t;
+ using pointer = element_type*;
+ using reference = element_type&;
+
+ using iterator = details::span_iterator<span<ElementType, Extent>, false>;
+ using const_iterator = details::span_iterator<span<ElementType, Extent>, true>;
+ using reverse_iterator = std::reverse_iterator<iterator>;
+ using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+
+ using size_type = index_type;
+
+#if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
+ static constexpr const index_type extent { Extent };
+#else
+ static constexpr index_type extent { Extent };
+#endif
+
+ // [span.cons], span constructors, copy, assignment, and destructor
+ template <bool Dependent = false,
+ // "Dependent" is needed to make "std::enable_if_t<Dependent || Extent <= 0>" SFINAE,
+ // since "std::enable_if_t<Extent <= 0>" is ill-formed when Extent is greater than 0.
+ class = std::enable_if_t<(Dependent || Extent <= 0)>>
+ constexpr span() noexcept : storage_(nullptr, details::extent_type<0>())
+ {
+ }
+
+ constexpr span(pointer ptr, index_type count) : storage_(ptr, count) {}
+
+ constexpr span(pointer firstElem, pointer lastElem)
+ : storage_(firstElem, std::distance(firstElem, lastElem))
+ {
+ }
+
+ template <std::size_t N>
+ constexpr span(element_type (&arr)[N]) noexcept
+ : storage_(KnownNotNull{&arr[0]}, details::extent_type<N>())
+ {
+ }
+
+ template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+ constexpr span(std::array<ArrayElementType, N>& arr) noexcept
+ : storage_(&arr[0], details::extent_type<N>())
+ {
+ }
+
+ template <std::size_t N>
+ constexpr span(const std::array<std::remove_const_t<element_type>, N>& arr) noexcept
+ : storage_(&arr[0], details::extent_type<N>())
+ {
+ }
+
+ // NB: the SFINAE here uses .data() as a incomplete/imperfect proxy for the requirement
+ // on Container to be a contiguous sequence container.
+ template <class Container,
+ class = std::enable_if_t<
+ !details::is_span<Container>::value && !details::is_std_array<Container>::value &&
+ std::is_convertible<typename Container::pointer, pointer>::value &&
+ std::is_convertible<typename Container::pointer,
+ decltype(std::declval<Container>().data())>::value>>
+ constexpr span(Container& cont) : span(cont.data(), narrow<index_type>(cont.size()))
+ {
+ }
+
+ template <class Container,
+ class = std::enable_if_t<
+ std::is_const<element_type>::value && !details::is_span<Container>::value &&
+ std::is_convertible<typename Container::pointer, pointer>::value &&
+ std::is_convertible<typename Container::pointer,
+ decltype(std::declval<Container>().data())>::value>>
+ constexpr span(const Container& cont) : span(cont.data(), narrow<index_type>(cont.size()))
+ {
+ }
+
+ constexpr span(const span& other) noexcept = default;
+
+ template <
+ class OtherElementType, std::ptrdiff_t OtherExtent,
+ class = std::enable_if_t<
+ details::is_allowed_extent_conversion<OtherExtent, Extent>::value &&
+ details::is_allowed_element_type_conversion<OtherElementType, element_type>::value>>
+ constexpr span(const span<OtherElementType, OtherExtent>& other)
+ : storage_(other.data(), details::extent_type<OtherExtent>(other.size()))
+ {
+ }
+
+ ~span() noexcept = default;
+ constexpr span& operator=(const span& other) noexcept = default;
+
+ // [span.sub], span subviews
+ template <std::ptrdiff_t Count>
+ constexpr span<element_type, Count> first() const
+ {
+ Expects(Count >= 0 && Count <= size());
+ return {data(), Count};
+ }
+
+ template <std::ptrdiff_t Count>
+ constexpr span<element_type, Count> last() const
+ {
+ Expects(Count >= 0 && size() - Count >= 0);
+ return {data() + (size() - Count), Count};
+ }
+
+ template <std::ptrdiff_t Offset, std::ptrdiff_t Count = dynamic_extent>
+ constexpr auto subspan() const -> typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type
+ {
+ Expects((Offset >= 0 && size() - Offset >= 0) &&
+ (Count == dynamic_extent || (Count >= 0 && Offset + Count <= size())));
+
+ return {data() + Offset, Count == dynamic_extent ? size() - Offset : Count};
+ }
+
+ constexpr span<element_type, dynamic_extent> first(index_type count) const
+ {
+ Expects(count >= 0 && count <= size());
+ return {data(), count};
+ }
+
+ constexpr span<element_type, dynamic_extent> last(index_type count) const
+ {
+ return make_subspan(size() - count, dynamic_extent, subspan_selector<Extent>{});
+ }
+
+ constexpr span<element_type, dynamic_extent> subspan(index_type offset,
+ index_type count = dynamic_extent) const
+ {
+ return make_subspan(offset, count, subspan_selector<Extent>{});
+ }
+
+
+ // [span.obs], span observers
+ constexpr index_type size() const noexcept { return storage_.size(); }
+ constexpr index_type size_bytes() const noexcept
+ {
+ return size() * narrow_cast<index_type>(sizeof(element_type));
+ }
+ constexpr bool empty() const noexcept { return size() == 0; }
+
+ // [span.elem], span element access
+ constexpr reference operator[](index_type idx) const
+ {
+ Expects(idx >= 0 && idx < storage_.size());
+ return data()[idx];
+ }
+
+ constexpr reference at(index_type idx) const { return this->operator[](idx); }
+ constexpr reference operator()(index_type idx) const { return this->operator[](idx); }
+ constexpr pointer data() const noexcept { return storage_.data(); }
+
+ // [span.iter], span iterator support
+ constexpr iterator begin() const noexcept { return {this, 0}; }
+ constexpr iterator end() const noexcept { return {this, size()}; }
+
+ constexpr const_iterator cbegin() const noexcept { return {this, 0}; }
+ constexpr const_iterator cend() const noexcept { return {this, size()}; }
+
+ constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
+ constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
+
+ constexpr const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator{cend()}; }
+ constexpr const_reverse_iterator crend() const noexcept { return const_reverse_iterator{cbegin()}; }
+
+#ifdef _MSC_VER
+ // Tell MSVC how to unwrap spans in range-based-for
+ constexpr pointer _Unchecked_begin() const noexcept { return data(); }
+ constexpr pointer _Unchecked_end() const noexcept { return data() + size(); }
+#endif // _MSC_VER
+
+private:
+
+ // Needed to remove unnecessary null check in subspans
+ struct KnownNotNull
+ {
+ pointer p;
+ };
+
+ // this implementation detail class lets us take advantage of the
+ // empty base class optimization to pay for only storage of a single
+ // pointer in the case of fixed-size spans
+ template <class ExtentType>
+ class storage_type : public ExtentType
+ {
+ public:
+ // KnownNotNull parameter is needed to remove unnecessary null check
+ // in subspans and constructors from arrays
+ template <class OtherExtentType>
+ constexpr storage_type(KnownNotNull data, OtherExtentType ext) : ExtentType(ext), data_(data.p)
+ {
+ Expects(ExtentType::size() >= 0);
+ }
+
+
+ template <class OtherExtentType>
+ constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data)
+ {
+ Expects(ExtentType::size() >= 0);
+ Expects(data || ExtentType::size() == 0);
+ }
+
+ constexpr pointer data() const noexcept { return data_; }
+
+ private:
+ pointer data_;
+ };
+
+ storage_type<details::extent_type<Extent>> storage_;
+
+ // The rest is needed to remove unnecessary null check
+ // in subspans and constructors from arrays
+ constexpr span(KnownNotNull ptr, index_type count) : storage_(ptr, count) {}
+
+ template <std::ptrdiff_t CallerExtent>
+ class subspan_selector {};
+
+ template <std::ptrdiff_t CallerExtent>
+ span<element_type, dynamic_extent> make_subspan(index_type offset,
+ index_type count,
+ subspan_selector<CallerExtent>) const
+ {
+ span<element_type, dynamic_extent> tmp(*this);
+ return tmp.subspan(offset, count);
+ }
+
+ span<element_type, dynamic_extent> make_subspan(index_type offset,
+ index_type count,
+ subspan_selector<dynamic_extent>) const
+ {
+ Expects(offset >= 0 && size() - offset >= 0);
+ if (count == dynamic_extent)
+ {
+ return { KnownNotNull{ data() + offset }, size() - offset };
+ }
+
+ Expects(count >= 0 && size() - offset >= count);
+ return { KnownNotNull{ data() + offset }, count };
+ }
+};
+
+#if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr const typename span<ElementType, Extent>::index_type span<ElementType, Extent>::extent;
+#endif
+
+
+// [span.comparison], span comparison operators
+template <class ElementType, std::ptrdiff_t FirstExtent, std::ptrdiff_t SecondExtent>
+constexpr bool operator==(span<ElementType, FirstExtent> l,
+ span<ElementType, SecondExtent> r)
+{
+ return std::equal(l.begin(), l.end(), r.begin(), r.end());
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator!=(span<ElementType, Extent> l,
+ span<ElementType, Extent> r)
+{
+ return !(l == r);
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator<(span<ElementType, Extent> l,
+ span<ElementType, Extent> r)
+{
+ return std::lexicographical_compare(l.begin(), l.end(), r.begin(), r.end());
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator<=(span<ElementType, Extent> l,
+ span<ElementType, Extent> r)
+{
+ return !(l > r);
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator>(span<ElementType, Extent> l,
+ span<ElementType, Extent> r)
+{
+ return r < l;
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator>=(span<ElementType, Extent> l,
+ span<ElementType, Extent> r)
+{
+ return !(l < r);
+}
+
+namespace details
+{
+ // if we only supported compilers with good constexpr support then
+ // this pair of classes could collapse down to a constexpr function
+
+ // we should use a narrow_cast<> to go to std::size_t, but older compilers may not see it as
+ // constexpr
+ // and so will fail compilation of the template
+ template <class ElementType, std::ptrdiff_t Extent>
+ struct calculate_byte_size
+ : std::integral_constant<std::ptrdiff_t,
+ static_cast<std::ptrdiff_t>(sizeof(ElementType) *
+ static_cast<std::size_t>(Extent))>
+ {
+ };
+
+ template <class ElementType>
+ struct calculate_byte_size<ElementType, dynamic_extent>
+ : std::integral_constant<std::ptrdiff_t, dynamic_extent>
+ {
+ };
+}
+
+// [span.objectrep], views of object representation
+template <class ElementType, std::ptrdiff_t Extent>
+span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_bytes(span<ElementType, Extent> s) noexcept
+{
+ return {reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
+}
+
+template <class ElementType, std::ptrdiff_t Extent,
+ class = std::enable_if_t<!std::is_const<ElementType>::value>>
+span<byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_writeable_bytes(span<ElementType, Extent> s) noexcept
+{
+ return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
+}
+
+//
+// make_span() - Utility functions for creating spans
+//
+template <class ElementType>
+constexpr span<ElementType> make_span(ElementType* ptr, typename span<ElementType>::index_type count)
+{
+ return span<ElementType>(ptr, count);
+}
+
+template <class ElementType>
+constexpr span<ElementType> make_span(ElementType* firstElem, ElementType* lastElem)
+{
+ return span<ElementType>(firstElem, lastElem);
+}
+
+template <class ElementType, std::size_t N>
+constexpr span<ElementType, N> make_span(ElementType (&arr)[N]) noexcept
+{
+ return span<ElementType, N>(arr);
+}
+
+template <class Container>
+constexpr span<typename Container::value_type> make_span(Container& cont)
+{
+ return span<typename Container::value_type>(cont);
+}
+
+template <class Container>
+constexpr span<const typename Container::value_type> make_span(const Container& cont)
+{
+ return span<const typename Container::value_type>(cont);
+}
+
+template <class Ptr>
+constexpr span<typename Ptr::element_type> make_span(Ptr& cont, std::ptrdiff_t count)
+{
+ return span<typename Ptr::element_type>(cont, count);
+}
+
+template <class Ptr>
+constexpr span<typename Ptr::element_type> make_span(Ptr& cont)
+{
+ return span<typename Ptr::element_type>(cont);
+}
+
+// Specialization of gsl::at for span
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr ElementType& at(span<ElementType, Extent> s, index i)
+{
+ // No bounds checking here because it is done in span::operator[] called below
+ return s[i];
+}
+
+} // namespace gsl
+
+#ifdef _MSC_VER
+#if _MSC_VER < 1910
+#undef constexpr
+#pragma pop_macro("constexpr")
+
+#endif // _MSC_VER < 1910
+
+#pragma warning(pop)
+#endif // _MSC_VER
+
+#if __GNUC__ > 6
+#pragma GCC diagnostic pop
+#endif // __GNUC__ > 6
+
+#endif // GSL_SPAN_H