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