Cleanup include structure, constexpr and noexcept compiler workarounds.
* Nest "gsl" directory inside a new "include" directory.
* Cleanup the _MSC_VER conditionals a bit; use constexpr on VS2017+.
* Don't #define noexcept on non-Microsoft implementations.
* Workaround VS2017 bug in multi_span. (Also implement == and != for static_bounds_dynamic_range_t because I'm an EoP semantic soundness snob.)
Fixes #441.
diff --git a/include/gsl/span b/include/gsl/span
new file mode 100644
index 0000000..79169f9
--- /dev/null
+++ b/include/gsl/span
@@ -0,0 +1,701 @@
+
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#pragma once
+
+#ifndef GSL_SPAN_H
+#define GSL_SPAN_H
+
+#include <gsl/gsl_assert>
+#include <gsl/gsl_byte>
+#include <gsl/gsl_util>
+#include <array>
+#include <iterator>
+#include <limits>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
+#include <memory>
+
+#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
+
+ // 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*/
+
+ // VS 2013 workarounds
+ #if _MSC_VER <= 1800
+ #define GSL_MSVC_HAS_VARIADIC_CTOR_BUG
+ #define GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+ #define GSL_MSVC_NO_CPP14_STD_EQUAL
+
+ // noexcept is not understood
+ #pragma push_macro("noexcept")
+ #define noexcept /*noexcept*/
+
+ #pragma push_macro("alignof")
+ #define alignof __alignof
+
+ // turn off some misguided warnings
+ #pragma warning(disable : 4351) // warns about newly introduced aggregate initializer behavior
+ #pragma warning(disable : 4512) // warns that assignment op could not be generated
+ #endif // _MSC_VER <= 1800
+ #endif // _MSC_VER < 1910
+#endif // _MSC_VER
+
+#ifdef GSL_THROW_ON_CONTRACT_VIOLATION
+ #define GSL_NOEXCEPT /*noexcept*/
+#else
+ #define GSL_NOEXCEPT noexcept
+#endif // GSL_THROW_ON_CONTRACT_VIOLATION
+
+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, 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:
+ using iterator_category = std::random_access_iterator_tag;
+ using value_type = std::remove_const_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>;
+
+ constexpr span_iterator() GSL_NOEXCEPT : span_iterator(nullptr, 0) {}
+
+ constexpr span_iterator(const Span* span, typename Span::index_type index)
+ : span_(span), index_(index)
+ {
+ Expects(span == nullptr || (index_ >= 0 && index <= span_->length()));
+ }
+
+ friend class span_iterator<Span, true>;
+ constexpr span_iterator(const span_iterator<Span, false>& other) GSL_NOEXCEPT
+ : span_iterator(other.span_, other.index_)
+ {
+ }
+
+ constexpr span_iterator<Span, IsConst>& operator=(const span_iterator<Span, IsConst>&) GSL_NOEXCEPT = default;
+
+ constexpr reference operator*() const
+ {
+ Expects(span_);
+ return (*span_)[index_];
+ }
+
+ constexpr pointer operator->() const
+ {
+ Expects(span_);
+ return &((*span_)[index_]);
+ }
+
+ constexpr span_iterator& operator++()
+ {
+ Expects(span_ && index_ >= 0 && index_ < span_->length());
+ ++index_;
+ return *this;
+ }
+
+ constexpr span_iterator operator++(int) GSL_NOEXCEPT
+ {
+ auto ret = *this;
+ ++(*this);
+ return ret;
+ }
+
+ constexpr span_iterator& operator--()
+ {
+ Expects(span_ && index_ > 0 && index_ <= span_->length());
+ --index_;
+ return *this;
+ }
+
+ constexpr span_iterator operator--(int) GSL_NOEXCEPT
+ {
+ auto ret = *this;
+ --(*this);
+ return ret;
+ }
+
+ constexpr span_iterator operator+(difference_type n) const GSL_NOEXCEPT
+ {
+ auto ret = *this;
+ return ret += n;
+ }
+
+ constexpr span_iterator& operator+=(difference_type n)
+ {
+ Expects(span_ && (index_ + n) >= 0 && (index_ + n) <= span_->length());
+ index_ += n;
+ return *this;
+ }
+
+ constexpr span_iterator operator-(difference_type n) const GSL_NOEXCEPT
+ {
+ auto ret = *this;
+ return ret -= n;
+ }
+
+ constexpr span_iterator& operator-=(difference_type n) GSL_NOEXCEPT { return *this += -n; }
+
+ constexpr difference_type operator-(const span_iterator& rhs) const
+ {
+ Expects(span_ == rhs.span_);
+ return index_ - rhs.index_;
+ }
+
+ constexpr reference operator[](difference_type n) const GSL_NOEXCEPT { return *(*this + n); }
+
+ constexpr friend bool operator==(const span_iterator& lhs,
+ const span_iterator& rhs) GSL_NOEXCEPT
+ {
+ return lhs.span_ == rhs.span_ && lhs.index_ == rhs.index_;
+ }
+
+ constexpr friend bool operator!=(const span_iterator& lhs,
+ const span_iterator& rhs) GSL_NOEXCEPT
+ {
+ return !(lhs == rhs);
+ }
+
+ constexpr friend bool operator<(const span_iterator& lhs, const span_iterator& rhs)
+ {
+ Expects(lhs.span_ == rhs.span_);
+ return lhs.index_ < rhs.index_;
+ }
+
+ constexpr friend bool operator<=(const span_iterator& lhs,
+ const span_iterator& rhs) GSL_NOEXCEPT
+ {
+ return !(rhs < lhs);
+ }
+
+ constexpr friend bool operator>(const span_iterator& lhs, const span_iterator& rhs) GSL_NOEXCEPT
+ {
+ return rhs < lhs;
+ }
+
+ constexpr friend bool operator>=(const span_iterator& lhs,
+ const span_iterator& rhs) GSL_NOEXCEPT
+ {
+ return !(rhs > lhs);
+ }
+
+ void swap(span_iterator& rhs) GSL_NOEXCEPT
+ {
+ std::swap(index_, rhs.index_);
+ std::swap(span_, rhs.span_);
+ }
+
+ protected:
+ const Span* span_;
+ std::ptrdiff_t index_;
+ };
+
+ template <class Span, bool IsConst>
+ inline constexpr span_iterator<Span, IsConst>
+ operator+(typename span_iterator<Span, IsConst>::difference_type n,
+ const span_iterator<Span, IsConst>& rhs) GSL_NOEXCEPT
+ {
+ return rhs + n;
+ }
+
+ template <class Span, bool IsConst>
+ inline constexpr span_iterator<Span, IsConst>
+ operator-(typename span_iterator<Span, IsConst>::difference_type n,
+ const span_iterator<Span, IsConst>& rhs) GSL_NOEXCEPT
+ {
+ return rhs - n;
+ }
+
+ 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() GSL_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 GSL_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 GSL_NOEXCEPT { return size_; }
+
+ private:
+ index_type size_;
+ };
+} // namespace details
+
+// [span], class template span
+template <class ElementType, std::ptrdiff_t Extent>
+class span
+{
+public:
+ // constants and types
+ using element_type = 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>;
+
+ constexpr static const index_type extent = Extent;
+
+ // [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() GSL_NOEXCEPT : storage_(nullptr, details::extent_type<0>()) {}
+
+ constexpr span(std::nullptr_t) GSL_NOEXCEPT : span() {}
+
+ constexpr span(pointer ptr, index_type count) : storage_(ptr, count) {}
+
+ constexpr span(pointer firstElem, pointer lastElem)
+ : storage_(firstElem, std::distance(firstElem, lastElem))
+ {
+ }
+
+ template <size_t N>
+ constexpr span(element_type (&arr)[N]) GSL_NOEXCEPT : storage_(&arr[0], details::extent_type<N>())
+ {
+ }
+
+ template <size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+ constexpr span(std::array<ArrayElementType, N>& arr) GSL_NOEXCEPT
+ : storage_(&arr[0], details::extent_type<N>())
+ {
+ }
+
+ template <size_t N>
+ constexpr span(const std::array<std::remove_const_t<element_type>, N>& arr) GSL_NOEXCEPT
+ : storage_(&arr[0], details::extent_type<N>())
+ {
+ }
+
+ template<class ArrayElementType = std::add_pointer<element_type>>
+ constexpr span(const std::unique_ptr<ArrayElementType>& ptr, index_type count) : storage_(ptr.get(), count) {}
+
+ constexpr span(const std::unique_ptr<ElementType>& ptr) : storage_(ptr.get(), ptr.get() ? 1 : 0) {}
+ constexpr span(const std::shared_ptr<ElementType>& ptr) : storage_(ptr.get(), ptr.get() ? 1 : 0) {}
+
+ // 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) GSL_NOEXCEPT = default;
+#ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+ constexpr span(span&& other) GSL_NOEXCEPT = default;
+#else
+ constexpr span(span&& other) GSL_NOEXCEPT : storage_(std::move(other.storage_)) {}
+#endif
+
+ 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()))
+ {
+ }
+
+ 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(span<OtherElementType, OtherExtent>&& other)
+ : storage_(other.data(), details::extent_type<OtherExtent>(other.size()))
+ {
+ }
+
+ ~span() GSL_NOEXCEPT = default;
+ constexpr span& operator=(const span& other) GSL_NOEXCEPT = default;
+
+#ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+ constexpr span& operator=(span&& other) GSL_NOEXCEPT = default;
+#else
+ constexpr span& operator=(span&& other) GSL_NOEXCEPT
+ {
+ storage_ = std::move(other.storage_);
+ return *this;
+ }
+#endif
+ // [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 && Count <= size());
+ return {data() + (size() - Count), Count};
+ }
+
+ template <std::ptrdiff_t Offset, std::ptrdiff_t Count = dynamic_extent>
+ constexpr span<element_type, Count> subspan() const
+ {
+ Expects((Offset == 0 || (Offset > 0 && Offset <= size())) &&
+ (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
+ {
+ Expects(count >= 0 && count <= size());
+ return {data() + (size() - count), count};
+ }
+
+ constexpr span<element_type, dynamic_extent> subspan(index_type offset,
+ index_type count = dynamic_extent) const
+ {
+ Expects((offset == 0 || (offset > 0 && offset <= size())) &&
+ (count == dynamic_extent || (count >= 0 && offset + count <= size())));
+ return {data() + offset, count == dynamic_extent ? size() - offset : count};
+ }
+
+ // [span.obs], span observers
+ constexpr index_type length() const GSL_NOEXCEPT { return size(); }
+ constexpr index_type size() const GSL_NOEXCEPT { return storage_.size(); }
+ constexpr index_type length_bytes() const GSL_NOEXCEPT { return size_bytes(); }
+ constexpr index_type size_bytes() const GSL_NOEXCEPT { return size() * narrow_cast<index_type>(sizeof(element_type)); }
+ constexpr bool empty() const GSL_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 GSL_NOEXCEPT { return storage_.data(); }
+
+ // [span.iter], span iterator support
+ iterator begin() const GSL_NOEXCEPT { return {this, 0}; }
+ iterator end() const GSL_NOEXCEPT { return {this, length()}; }
+
+ const_iterator cbegin() const GSL_NOEXCEPT { return {this, 0}; }
+ const_iterator cend() const GSL_NOEXCEPT { return {this, length()}; }
+
+ reverse_iterator rbegin() const GSL_NOEXCEPT { return reverse_iterator{end()}; }
+ reverse_iterator rend() const GSL_NOEXCEPT { return reverse_iterator{begin()}; }
+
+ const_reverse_iterator crbegin() const GSL_NOEXCEPT { return const_reverse_iterator{cend()}; }
+ const_reverse_iterator crend() const GSL_NOEXCEPT { return const_reverse_iterator{cbegin()}; }
+
+private:
+ // 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:
+ template <class OtherExtentType>
+ constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data)
+ {
+ Expects((!data && ExtentType::size() == 0) || (data && ExtentType::size() >= 0));
+ }
+
+ constexpr pointer data() const GSL_NOEXCEPT { return data_; }
+
+ private:
+ pointer data_;
+ };
+
+ storage_type<details::extent_type<Extent>> storage_;
+};
+
+// [span.comparison], span comparison operators
+template <class ElementType, std::ptrdiff_t FirstExtent, std::ptrdiff_t SecondExtent>
+inline constexpr bool operator==(const span<ElementType, FirstExtent>& l,
+ const span<ElementType, SecondExtent>& r)
+{
+#ifdef GSL_MSVC_NO_CPP14_STD_EQUAL
+ return (l.size() == r.size()) && std::equal(l.begin(), l.end(), r.begin());
+#else
+ return std::equal(l.begin(), l.end(), r.begin(), r.end());
+#endif
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+inline constexpr bool operator!=(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+ return !(l == r);
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+inline constexpr bool operator<(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+ return std::lexicographical_compare(l.begin(), l.end(), r.begin(), r.end());
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+inline constexpr bool operator<=(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+ return !(l > r);
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+inline constexpr bool operator>(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+ return r < l;
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+inline constexpr bool operator>=(const span<ElementType, Extent>& l, const 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 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) GSL_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) GSL_NOEXCEPT
+{
+ return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
+}
+
+//
+// make_span() - Utility functions for creating spans
+//
+template <class ElementType>
+span<ElementType>
+make_span(ElementType* ptr, typename span<ElementType>::index_type count)
+{ return span<ElementType>(ptr, count); }
+
+template <class ElementType>
+span<ElementType>
+make_span(ElementType* firstElem, ElementType* lastElem)
+{ return span<ElementType>(firstElem, lastElem); }
+
+template <class ElementType, size_t N>
+span<ElementType>
+make_span(ElementType (&arr)[N])
+{ return span<ElementType>(arr); }
+
+template <class Container>
+span<typename Container::value_type>
+make_span(Container &cont)
+{ return span<typename Container::value_type>(cont); }
+
+template <class Container>
+span<const typename Container::value_type>
+make_span(const Container &cont)
+{ return span<const typename Container::value_type>(cont); }
+
+template <class Ptr>
+span<typename Ptr::element_type>
+make_span(Ptr& cont, std::ptrdiff_t count)
+{ return span<typename Ptr::element_type>(cont, count); }
+
+template <class Ptr>
+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>
+inline constexpr ElementType& at(const span<ElementType, Extent>& s, std::ptrdiff_t index)
+{
+ // No bounds checking here because it is done in span::operator[] called below
+ return s[index];
+}
+
+} // namespace gsl
+
+#undef GSL_NOEXCEPT
+
+#ifdef _MSC_VER
+ #if _MSC_VER < 1910
+ #undef constexpr
+ #pragma pop_macro("constexpr")
+
+ #if _MSC_VER <= 1800
+ #undef noexcept
+ #pragma pop_macro("noexcept")
+
+ #undef alignof
+ #pragma pop_macro("alignof")
+
+ #undef GSL_MSVC_HAS_VARIADIC_CTOR_BUG
+ #undef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+ #undef GSL_MSVC_NO_CPP14_STD_EQUAL
+ #endif // _MSC_VER <= 1800
+ #endif // _MSC_VER < 1910
+
+ #pragma warning(pop)
+#endif // _MSC_VER
+
+#endif // GSL_SPAN_H