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.

include/gsl/gsl

@@ -0,0 +1,164 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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_GSL_H
+#define GSL_GSL_H
+
+#include <gsl/gsl_assert>  // Ensures/Expects
+#include <gsl/gsl_util>    // finally()/narrow()/narrow_cast()...
+#include <gsl/multi_span>  // multi_span, strided_span...
+#include <gsl/span>        // span
+#include <gsl/string_span> // zstring, string_span, zstring_builder...
+#include <memory>
+
+#if defined(_MSC_VER) && _MSC_VER < 1910
+ #pragma push_macro("constexpr")
+ #define constexpr /*constexpr*/
+
+ // MSVC 2013 workarounds
+ #if _MSC_VER <= 1800
+  // noexcept is not understood
+  #pragma push_macro("noexcept")
+  #define noexcept /*noexcept*/
+
+  // turn off some misguided warnings
+  #pragma warning(push)
+  #pragma warning(disable : 4351) // warns about newly introduced aggregate initializer behavior
+ #endif // _MSC_VER <= 1800
+#endif // defined(_MSC_VER) && _MSC_VER < 1910
+
+namespace gsl
+{
+
+//
+// GSL.owner: ownership pointers
+//
+using std::unique_ptr;
+using std::shared_ptr;
+
+template <class T>
+using owner = T;
+
+//
+// not_null
+//
+// Restricts a pointer or smart pointer to only hold non-null values.
+//
+// Has zero size overhead over T.
+//
+// If T is a pointer (i.e. T == U*) then
+// - allow construction from U* or U&
+// - disallow construction from nullptr_t
+// - disallow default construction
+// - ensure construction from U* fails with nullptr
+// - allow implicit conversion to U*
+//
+template <class T>
+class not_null
+{
+    static_assert(std::is_assignable<T&, std::nullptr_t>::value, "T cannot be assigned nullptr.");
+
+public:
+    not_null(T t) : ptr_(t) { ensure_invariant(); }
+    not_null& operator=(const T& t)
+    {
+        ptr_ = t;
+        ensure_invariant();
+        return *this;
+    }
+
+    not_null(const not_null& other) = default;
+    not_null& operator=(const not_null& other) = default;
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    not_null(const not_null<U>& other)
+    {
+        *this = other;
+    }
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    not_null& operator=(const not_null<U>& other)
+    {
+        ptr_ = other.get();
+        return *this;
+    }
+
+    // prevents compilation when someone attempts to assign a nullptr
+    not_null(std::nullptr_t) = delete;
+    not_null(int) = delete;
+    not_null<T>& operator=(std::nullptr_t) = delete;
+    not_null<T>& operator=(int) = delete;
+
+    T get() const
+    {
+#ifdef _MSC_VER
+        __assume(ptr_ != nullptr);
+#endif
+        return ptr_;
+    } // the assume() should help the optimizer
+
+    operator T() const { return get(); }
+    T operator->() const { return get(); }
+
+    bool operator==(const T& rhs) const { return ptr_ == rhs; }
+    bool operator!=(const T& rhs) const { return !(*this == rhs); }
+private:
+    T ptr_;
+
+    // we assume that the compiler can hoist/prove away most of the checks inlined from this
+    // function
+    // if not, we could make them optional via conditional compilation
+    void ensure_invariant() const { Expects(ptr_ != nullptr); }
+
+    // unwanted operators...pointers only point to single objects!
+    // TODO ensure all arithmetic ops on this type are unavailable
+    not_null<T>& operator++() = delete;
+    not_null<T>& operator--() = delete;
+    not_null<T> operator++(int) = delete;
+    not_null<T> operator--(int) = delete;
+    not_null<T>& operator+(size_t) = delete;
+    not_null<T>& operator+=(size_t) = delete;
+    not_null<T>& operator-(size_t) = delete;
+    not_null<T>& operator-=(size_t) = delete;
+};
+
+} // namespace gsl
+
+namespace std
+{
+template <class T>
+struct hash<gsl::not_null<T>>
+{
+    size_t operator()(const gsl::not_null<T>& value) const { return hash<T>{}(value); }
+};
+
+} // namespace std
+
+#if defined(_MSC_VER) && _MSC_VER < 1910
+ #undef constexpr
+ #pragma pop_macro("constexpr")
+
+ #if _MSC_VER <= 1800
+  #undef noexcept
+  #pragma pop_macro("noexcept")
+
+  #pragma warning(pop)
+ #endif // _MSC_VER <= 1800
+#endif // defined(_MSC_VER) && _MSC_VER < 1910
+
+#endif // GSL_GSL_H

include/gsl/gsl_algorithm

@@ -0,0 +1,59 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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_ALGORITHM_H
+#define GSL_ALGORITHM_H
+
+#include <gsl/span>
+#include <algorithm>
+
+#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)
+#endif // _MSC_VER
+
+namespace gsl
+{
+
+template <class SrcElementType, std::ptrdiff_t SrcExtent,
+          class DestElementType, std::ptrdiff_t DestExtent>
+void copy(span<SrcElementType, SrcExtent> src, span<DestElementType, DestExtent> dest)
+{
+    static_assert(std::is_assignable<decltype(*dest.data()), decltype(*src.data())>::value,
+                  "Elements of source span can not be assigned to elements of destination span");
+    static_assert(SrcExtent == dynamic_extent || DestExtent == dynamic_extent || (SrcExtent <= DestExtent),
+                  "Source range is longer than target range");
+
+    Expects(dest.size() >= src.size());
+    std::copy_n(src.data(), src.size(), dest.data());
+}
+
+} // namespace gsl
+
+#ifdef _MSC_VER
+ #pragma warning(pop)
+#endif // _MSC_VER
+
+#endif // GSL_ALGORITHM_H

include/gsl/gsl_assert

@@ -0,0 +1,85 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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_CONTRACTS_H
+#define GSL_CONTRACTS_H
+
+#include <exception>
+#include <stdexcept>
+
+//
+// There are three configuration options for this GSL implementation's behavior
+// when pre/post conditions on the GSL types are violated:
+//
+// 1. GSL_TERMINATE_ON_CONTRACT_VIOLATION: std::terminate will be called (default)
+// 2. GSL_THROW_ON_CONTRACT_VIOLATION: a gsl::fail_fast exception will be thrown
+// 3. GSL_UNENFORCED_ON_CONTRACT_VIOLATION: nothing happens
+//
+#if !(defined(GSL_THROW_ON_CONTRACT_VIOLATION) || defined(GSL_TERMINATE_ON_CONTRACT_VIOLATION) ||    \
+      defined(GSL_UNENFORCED_ON_CONTRACT_VIOLATION))
+#define GSL_TERMINATE_ON_CONTRACT_VIOLATION
+#endif
+
+#define GSL_STRINGIFY_DETAIL(x) #x
+#define GSL_STRINGIFY(x) GSL_STRINGIFY_DETAIL(x)
+
+#if defined(__clang__) || defined(__GNUC__)
+#define GSL_LIKELY(x) __builtin_expect (!!(x), 1)
+#define GSL_UNLIKELY(x) __builtin_expect (!!(x), 0)
+#else
+#define GSL_LIKELY(x) (x)
+#define GSL_UNLIKELY(x) (x)
+#endif
+
+//
+// GSL.assert: assertions
+//
+
+namespace gsl
+{
+struct fail_fast : public std::runtime_error
+{
+    explicit fail_fast(char const* const message) : std::runtime_error(message) {}
+};
+}
+
+#if defined(GSL_THROW_ON_CONTRACT_VIOLATION)
+
+#define Expects(cond)                                                                              \
+    if (GSL_UNLIKELY(!(cond)))                                                                     \
+        throw gsl::fail_fast("GSL: Precondition failure at " __FILE__ ": " GSL_STRINGIFY(__LINE__));
+#define Ensures(cond)                                                                              \
+    if (GSL_UNLIKELY(!(cond)))                                                                     \
+        throw gsl::fail_fast("GSL: Postcondition failure at " __FILE__                             \
+                             ": " GSL_STRINGIFY(__LINE__));
+
+#elif defined(GSL_TERMINATE_ON_CONTRACT_VIOLATION)
+
+#define Expects(cond)                                                                              \
+    if (GSL_UNLIKELY(!(cond))) std::terminate();
+#define Ensures(cond)                                                                              \
+    if (GSL_UNLIKELY(!(cond))) std::terminate();
+
+#elif defined(GSL_UNENFORCED_ON_CONTRACT_VIOLATION)
+
+#define Expects(cond)
+#define Ensures(cond)
+
+#endif
+
+#endif // GSL_CONTRACTS_H

include/gsl/gsl_byte

@@ -0,0 +1,155 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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_BYTE_H
+#define GSL_BYTE_H
+
+#include <type_traits>
+
+#ifdef _MSC_VER
+ #pragma warning(push)
+
+ // don't warn about function style casts in byte related operators
+ #pragma warning(disable : 26493)
+
+ // MSVC 2013 workarounds
+ #if _MSC_VER <= 1800
+  // constexpr is not understood
+  #pragma push_macro("constexpr")
+  #define constexpr inline
+
+  // noexcept is not understood
+  #pragma push_macro("noexcept")
+  #define noexcept /*noexcept*/
+ #endif // _MSC_VER <= 1800
+#endif // _MSC_VER
+
+namespace gsl
+{
+// This is a simple definition for now that allows
+// use of byte within span<> to be standards-compliant
+enum class byte : unsigned char
+{
+};
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr byte& operator<<=(byte& b, IntegerType shift) noexcept
+{
+    return b = byte(static_cast<unsigned char>(b) << shift);
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr byte operator<<(byte b, IntegerType shift) noexcept
+{
+    return byte(static_cast<unsigned char>(b) << shift);
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr byte& operator>>=(byte& b, IntegerType shift) noexcept
+{
+    return b = byte(static_cast<unsigned char>(b) >> shift);
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr byte operator>>(byte b, IntegerType shift) noexcept
+{
+    return byte(static_cast<unsigned char>(b) >> shift);
+}
+
+inline constexpr byte& operator|=(byte& l, byte r) noexcept
+{
+    return l = byte(static_cast<unsigned char>(l) | static_cast<unsigned char>(r));
+}
+
+inline constexpr byte operator|(byte l, byte r) noexcept
+{
+    return byte(static_cast<unsigned char>(l) | static_cast<unsigned char>(r));
+}
+
+inline constexpr byte& operator&=(byte& l, byte r) noexcept
+{
+    return l = byte(static_cast<unsigned char>(l) & static_cast<unsigned char>(r));
+}
+
+inline constexpr byte operator&(byte l, byte r) noexcept
+{
+    return byte(static_cast<unsigned char>(l) & static_cast<unsigned char>(r));
+}
+
+inline constexpr byte& operator^=(byte& l, byte r) noexcept
+{
+    return l = byte(static_cast<unsigned char>(l) ^ static_cast<unsigned char>(r));
+}
+
+inline constexpr byte operator^(byte l, byte r) noexcept
+{
+    return byte(static_cast<unsigned char>(l) ^ static_cast<unsigned char>(r));
+}
+
+inline constexpr byte operator~(byte b) noexcept { return byte(~static_cast<unsigned char>(b)); }
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr IntegerType to_integer(byte b) noexcept
+{
+    return static_cast<IntegerType>(b);
+}
+
+template<bool E, typename T>
+inline constexpr byte to_byte_impl(T t) noexcept
+{
+    static_assert(
+        E,
+        "gsl::to_byte(t) must be provided an unsigned char, otherwise data loss may occur. "
+        "If you are calling to_byte with an integer contant use: gsl::to_byte<t>() version."
+    );
+    return static_cast<byte>(t);
+}
+template<>
+inline constexpr byte to_byte_impl<true, unsigned char>(unsigned char t) noexcept
+{
+     return byte(t);
+}
+
+template<typename T>
+inline constexpr byte to_byte(T t) noexcept
+{
+     return to_byte_impl<std::is_same<T, unsigned char>::value, T>(t);
+}
+
+template <int I>
+inline constexpr byte to_byte() noexcept
+{
+    static_assert(I >= 0 && I <= 255, "gsl::byte only has 8 bits of storage, values must be in range 0-255");
+    return static_cast<byte>(I);
+}
+
+} // namespace gsl
+
+#ifdef _MSC_VER
+ #if _MSC_VER <= 1800
+  #undef constexpr
+  #pragma pop_macro("constexpr")
+
+  #undef noexcept
+  #pragma pop_macro("noexcept")
+ #endif // _MSC_VER <= 1800
+
+ #pragma warning(pop)
+#endif // _MSC_VER
+
+#endif // GSL_BYTE_H

include/gsl/gsl_util

@@ -0,0 +1,175 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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_UTIL_H
+#define GSL_UTIL_H
+
+#include <gsl/gsl_assert> // Ensures/Expects
+#include <array>
+#include <exception>
+#include <type_traits>
+#include <utility>
+
+#if defined(_MSC_VER)
+ #pragma warning(push)
+ #pragma warning(disable : 4127) // conditional expression is constant
+
+ #if _MSC_VER < 1910
+  #pragma push_macro("constexpr")
+  #define constexpr /*constexpr*/
+  // MSVC 2013 workarounds
+  #if _MSC_VER <= 1800
+   // noexcept is not understood
+   #pragma push_macro("noexcept")
+   #define noexcept /*noexcept*/
+   // turn off some misguided warnings
+   #pragma warning(disable : 4351) // warns about newly introduced aggregate initializer behavior
+  #endif // _MSC_VER <= 1800
+ #endif // _MSC_VER < 1910
+#endif // _MSC_VER
+
+namespace gsl
+{
+//
+// GSL.util: utilities
+//
+
+// final_act allows you to ensure something gets run at the end of a scope
+template <class F>
+class final_act
+{
+public:
+    explicit final_act(F f) noexcept : f_(std::move(f)), invoke_(true) {}
+
+    final_act(final_act&& other) noexcept : f_(std::move(other.f_)), invoke_(other.invoke_)
+    {
+        other.invoke_ = false;
+    }
+
+    final_act(const final_act&) = delete;
+    final_act& operator=(const final_act&) = delete;
+
+    ~final_act() noexcept
+    {
+        if (invoke_) f_();
+    }
+
+private:
+    F f_;
+    bool invoke_;
+};
+
+// finally() - convenience function to generate a final_act
+template <class F>
+inline final_act<F> finally(const F& f) noexcept
+{
+    return final_act<F>(f);
+}
+
+template <class F>
+inline final_act<F> finally(F&& f) noexcept
+{
+    return final_act<F>(std::forward<F>(f));
+}
+
+// narrow_cast(): a searchable way to do narrowing casts of values
+#if defined(_MSC_VER) && _MSC_VER <= 1800
+template <class T, class U>
+inline constexpr T narrow_cast(U u) noexcept
+{
+    return static_cast<T>(u);
+}
+#else
+template <class T, class U>
+inline constexpr T narrow_cast(U&& u) noexcept
+{
+    return static_cast<T>(std::forward<U>(u));
+}
+#endif
+
+struct narrowing_error : public std::exception
+{
+};
+
+namespace details
+{
+    template <class T, class U>
+    struct is_same_signedness
+        : public std::integral_constant<bool, std::is_signed<T>::value == std::is_signed<U>::value>
+    {
+    };
+}
+
+// narrow() : a checked version of narrow_cast() that throws if the cast changed the value
+template <class T, class U>
+inline T narrow(U u)
+{
+    T t = narrow_cast<T>(u);
+    if (static_cast<U>(t) != u) throw narrowing_error();
+    if (!details::is_same_signedness<T, U>::value && ((t < T{}) != (u < U{})))
+        throw narrowing_error();
+    return t;
+}
+
+//
+// at() - Bounds-checked way of accessing static arrays, std::array, std::vector
+//
+template <class T, size_t N>
+inline constexpr T& at(T (&arr)[N], std::ptrdiff_t index)
+{
+    Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(N));
+    return arr[static_cast<size_t>(index)];
+}
+
+template <class T, size_t N>
+inline constexpr T& at(std::array<T, N>& arr, std::ptrdiff_t index)
+{
+    Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(N));
+    return arr[static_cast<size_t>(index)];
+}
+
+template <class Cont>
+inline constexpr typename Cont::value_type& at(Cont& cont, std::ptrdiff_t index)
+{
+    Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(cont.size()));
+    return cont[static_cast<typename Cont::size_type>(index)];
+}
+
+template <class T>
+inline constexpr const T& at(std::initializer_list<T> cont, std::ptrdiff_t index)
+{
+    Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(cont.size()));
+    return *(cont.begin() + index);
+}
+
+} // namespace gsl
+
+#if defined(_MSC_VER)
+ #if _MSC_VER < 1910
+  #undef constexpr
+  #pragma pop_macro("constexpr")
+
+  #if _MSC_VER <= 1800
+   #undef noexcept
+   #pragma pop_macro("noexcept")
+  #endif // _MSC_VER <= 1800
+ #endif // _MSC_VER < 1910
+ #pragma warning(pop)
+#endif // _MSC_VER
+
+#endif // GSL_UTIL_H

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

include/gsl/string_span

@@ -0,0 +1,852 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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_STRING_SPAN_H
+#define GSL_STRING_SPAN_H
+
+#include <gsl/gsl_assert>
+#include <gsl/gsl_util>
+#include <gsl/span>
+#include <cstdint>
+#include <cstring>
+#include <string>
+
+#ifdef _MSC_VER
+ #pragma warning(push)
+
+ // 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_TYPE_DEDUCTION_BUG
+   #define GSL_MSVC_HAS_SFINAE_SUBSTITUTION_ICE
+   #define GSL_MSVC_NO_CPP14_STD_EQUAL
+   #define GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+
+   // noexcept is not understood
+   #pragma push_macro("noexcept")
+   #define noexcept /*noexcept*/
+  #endif // _MSC_VER <= 1800
+ #endif // _MSC_VER < 1910
+#endif // _MSC_VER
+
+// In order to test the library, we need it to throw exceptions that we can catch
+#ifdef GSL_THROW_ON_CONTRACT_VIOLATION
+ #define GSL_NOEXCEPT /*noexcept*/
+#else
+ #define GSL_NOEXCEPT noexcept
+#endif // GSL_THROW_ON_CONTRACT_VIOLATION
+
+namespace gsl
+{
+//
+// czstring and wzstring
+//
+// These are "tag" typedefs for C-style strings (i.e. null-terminated character arrays)
+// that allow static analysis to help find bugs.
+//
+// There are no additional features/semantics that we can find a way to add inside the
+// type system for these types that will not either incur significant runtime costs or
+// (sometimes needlessly) break existing programs when introduced.
+//
+
+template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
+using basic_zstring = CharT*;
+
+template <std::ptrdiff_t Extent = dynamic_extent>
+using czstring = basic_zstring<const char, Extent>;
+
+template <std::ptrdiff_t Extent = dynamic_extent>
+using cwzstring = basic_zstring<const wchar_t, Extent>;
+
+template <std::ptrdiff_t Extent = dynamic_extent>
+using zstring = basic_zstring<char, Extent>;
+
+template <std::ptrdiff_t Extent = dynamic_extent>
+using wzstring = basic_zstring<wchar_t, Extent>;
+
+namespace details
+{
+    inline std::ptrdiff_t string_length(const char *str, std::ptrdiff_t n)
+    {
+        if (str == nullptr || n <= 0)
+            return 0;
+
+        span<const char> str_span{str, n};
+
+        std::ptrdiff_t len = 0;
+        while (len < n && str_span[len])
+            len++;
+
+        return len;
+    }
+
+    inline std::ptrdiff_t wstring_length(const wchar_t *str, std::ptrdiff_t n)
+    {
+        if (str == nullptr || n <= 0)
+            return 0;
+
+        span<const wchar_t> str_span{str, n};
+
+        std::ptrdiff_t len = 0;
+        while (len < n && str_span[len])
+            len++;
+
+        return len;
+    }
+}
+
+//
+// ensure_sentinel()
+//
+// Provides a way to obtain an span from a contiguous sequence
+// that ends with a (non-inclusive) sentinel value.
+//
+// Will fail-fast if sentinel cannot be found before max elements are examined.
+//
+template <typename T, const T Sentinel>
+span<T, dynamic_extent> ensure_sentinel(T* seq, std::ptrdiff_t max = PTRDIFF_MAX)
+{
+    auto cur = seq;
+    while ((cur - seq) < max && *cur != Sentinel) ++cur;
+    Ensures(*cur == Sentinel);
+    return {seq, cur - seq};
+}
+
+//
+// ensure_z - creates a span for a czstring or cwzstring.
+// Will fail fast if a null-terminator cannot be found before
+// the limit of size_type.
+//
+template <typename T>
+inline span<T, dynamic_extent> ensure_z(T* const& sz, std::ptrdiff_t max = PTRDIFF_MAX)
+{
+    return ensure_sentinel<T, 0>(sz, max);
+}
+
+// TODO (neilmac) there is probably a better template-magic way to get the const and non-const
+// overloads to share an implementation
+inline span<char, dynamic_extent> ensure_z(char* const& sz, std::ptrdiff_t max)
+{
+    auto len = details::string_length(sz, max);
+    Ensures(sz[len] == 0);
+    return {sz, len};
+}
+
+inline span<const char, dynamic_extent> ensure_z(const char* const& sz, std::ptrdiff_t max)
+{
+    auto len = details::string_length(sz, max);
+    Ensures(sz[len] == 0);
+    return {sz, len};
+}
+
+inline span<wchar_t, dynamic_extent> ensure_z(wchar_t* const& sz, std::ptrdiff_t max)
+{
+    auto len = details::wstring_length(sz, max);
+    Ensures(sz[len] == 0);
+    return {sz, len};
+}
+
+inline span<const wchar_t, dynamic_extent> ensure_z(const wchar_t* const& sz, std::ptrdiff_t max)
+{
+    auto len = details::wstring_length(sz, max);
+    Ensures(sz[len] == 0);
+    return {sz, len};
+}
+
+template <typename T, size_t N>
+span<T, dynamic_extent> ensure_z(T (&sz)[N])
+{
+    return ensure_z(&sz[0], static_cast<std::ptrdiff_t>(N));
+}
+
+template <class Cont>
+span<typename std::remove_pointer<typename Cont::pointer>::type, dynamic_extent>
+ensure_z(Cont& cont)
+{
+    return ensure_z(cont.data(), static_cast<std::ptrdiff_t>(cont.length()));
+}
+
+template <typename CharT, std::ptrdiff_t>
+class basic_string_span;
+
+namespace details
+{
+    template <typename T>
+    struct is_basic_string_span_oracle : std::false_type
+    {
+    };
+
+    template <typename CharT, std::ptrdiff_t Extent>
+    struct is_basic_string_span_oracle<basic_string_span<CharT, Extent>> : std::true_type
+    {
+    };
+
+    template <typename T>
+    struct is_basic_string_span : is_basic_string_span_oracle<std::remove_cv_t<T>>
+    {
+    };
+
+    template <typename T>
+    struct length_func
+    {
+    };
+
+    template <>
+    struct length_func<char>
+    {
+        std::ptrdiff_t operator()(char* const ptr, std::ptrdiff_t length) GSL_NOEXCEPT
+        {
+            return details::string_length(ptr, length);
+        }
+    };
+
+    template <>
+    struct length_func<wchar_t>
+    {
+        std::ptrdiff_t operator()(wchar_t* const ptr, std::ptrdiff_t length) GSL_NOEXCEPT
+        {
+            return details::wstring_length(ptr, length);
+        }
+    };
+
+    template <>
+    struct length_func<const char>
+    {
+        std::ptrdiff_t operator()(const char* const ptr, std::ptrdiff_t length) GSL_NOEXCEPT
+        {
+            return details::string_length(ptr, length);
+        }
+    };
+
+    template <>
+    struct length_func<const wchar_t>
+    {
+        std::ptrdiff_t operator()(const wchar_t* const ptr, std::ptrdiff_t length) GSL_NOEXCEPT
+        {
+            return details::wstring_length(ptr, length);
+        }
+    };
+}
+
+//
+// string_span and relatives
+//
+template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
+class basic_string_span
+{
+public:
+    using element_type = CharT;
+    using pointer = std::add_pointer_t<element_type>;
+    using reference = std::add_lvalue_reference_t<element_type>;
+    using const_reference = std::add_lvalue_reference_t<std::add_const_t<element_type>>;
+    using impl_type = span<element_type, Extent>;
+
+    using index_type = typename impl_type::index_type;
+    using iterator = typename impl_type::iterator;
+    using const_iterator = typename impl_type::const_iterator;
+    using reverse_iterator = typename impl_type::reverse_iterator;
+    using const_reverse_iterator = typename impl_type::const_reverse_iterator;
+
+    // default (empty)
+    constexpr basic_string_span() GSL_NOEXCEPT = default;
+
+    // copy
+    constexpr basic_string_span(const basic_string_span& other) GSL_NOEXCEPT = default;
+
+// move
+#ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+    constexpr basic_string_span(basic_string_span&& other) GSL_NOEXCEPT = default;
+#else
+    constexpr basic_string_span(basic_string_span&& other) : span_(std::move(other.span_)) {}
+#endif
+
+    // assign
+    constexpr basic_string_span& operator=(const basic_string_span& other) GSL_NOEXCEPT = default;
+
+// move assign
+#ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+    constexpr basic_string_span& operator=(basic_string_span&& other) GSL_NOEXCEPT = default;
+#else
+    constexpr basic_string_span& operator=(basic_string_span&& other) GSL_NOEXCEPT
+    {
+        span_ = std::move(other.span_);
+        return *this;
+    }
+#endif
+
+    // from nullptr
+    constexpr basic_string_span(std::nullptr_t ptr) GSL_NOEXCEPT : span_(ptr) {}
+
+    constexpr basic_string_span(pointer ptr, index_type length) : span_(ptr, length) {}
+    constexpr basic_string_span(pointer firstElem, pointer lastElem) : span_(firstElem, lastElem) {}
+
+    // From static arrays - if 0-terminated, remove 0 from the view
+    // All other containers allow 0s within the length, so we do not remove them
+    template <size_t N>
+    constexpr basic_string_span(element_type (&arr)[N]) : span_(remove_z(arr))
+    {
+    }
+
+    template <size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr basic_string_span(std::array<ArrayElementType, N>& arr) GSL_NOEXCEPT : span_(arr)
+    {
+    }
+
+    template <size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr basic_string_span(const std::array<ArrayElementType, N>& arr) GSL_NOEXCEPT : span_(arr)
+    {
+    }
+
+    // Container signature should work for basic_string after C++17 version exists
+    template <class Traits, class Allocator>
+    constexpr basic_string_span(std::basic_string<element_type, Traits, Allocator>& str)
+        : span_(&str[0], narrow_cast<std::ptrdiff_t>(str.length()))
+    {
+    }
+
+    template <class Traits, class Allocator>
+    constexpr basic_string_span(const std::basic_string<element_type, Traits, Allocator>& str)
+        : span_(&str[0], str.length())
+    {
+    }
+
+    // from containers. Containers must have a pointer type and data() function signatures
+    template <class Container,
+              class = std::enable_if_t<
+                  !details::is_basic_string_span<Container>::value &&
+                  std::is_convertible<typename Container::pointer, pointer>::value &&
+                  std::is_convertible<typename Container::pointer,
+                                      decltype(std::declval<Container>().data())>::value>>
+    constexpr basic_string_span(Container& cont) : span_(cont)
+    {
+    }
+
+    template <class Container,
+              class = std::enable_if_t<
+                  !details::is_basic_string_span<Container>::value &&
+                  std::is_convertible<typename Container::pointer, pointer>::value &&
+                  std::is_convertible<typename Container::pointer,
+                                      decltype(std::declval<Container>().data())>::value>>
+    constexpr basic_string_span(const Container& cont) : span_(cont)
+    {
+    }
+
+    // from string_span
+    template <
+        class OtherValueType, std::ptrdiff_t OtherExtent,
+        class = std::enable_if_t<std::is_convertible<
+            typename basic_string_span<OtherValueType, OtherExtent>::impl_type, impl_type>::value>>
+    constexpr basic_string_span(basic_string_span<OtherValueType, OtherExtent> other)
+        : span_(other.data(), other.length())
+    {
+    }
+
+    template <index_type Count>
+    constexpr basic_string_span<element_type, Count> first() const
+    {
+        return {span_.template first<Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent> first(index_type count) const
+    {
+        return {span_.first(count)};
+    }
+
+    template <index_type Count>
+    constexpr basic_string_span<element_type, Count> last() const
+    {
+        return {span_.template last<Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent> last(index_type count) const
+    {
+        return {span_.last(count)};
+    }
+
+    template <index_type Offset, index_type Count>
+    constexpr basic_string_span<element_type, Count> subspan() const
+    {
+        return {span_.template subspan<Offset, Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent>
+    subspan(index_type offset, index_type count = dynamic_extent) const
+    {
+        return {span_.subspan(offset, count)};
+    }
+
+    constexpr reference operator[](index_type idx) const { return span_[idx]; }
+    constexpr reference operator()(index_type idx) const { return span_[idx]; }
+
+    constexpr pointer data() const { return span_.data(); }
+
+    constexpr index_type length() const GSL_NOEXCEPT { return span_.size(); }
+    constexpr index_type size() const GSL_NOEXCEPT { return span_.size(); }
+    constexpr index_type size_bytes() const GSL_NOEXCEPT { return span_.size_bytes(); }
+    constexpr index_type length_bytes() const GSL_NOEXCEPT { return span_.length_bytes(); }
+    constexpr bool empty() const GSL_NOEXCEPT { return size() == 0; }
+
+    constexpr iterator begin() const GSL_NOEXCEPT { return span_.begin(); }
+    constexpr iterator end() const GSL_NOEXCEPT { return span_.end(); }
+
+    constexpr const_iterator cbegin() const GSL_NOEXCEPT { return span_.cbegin(); }
+    constexpr const_iterator cend() const GSL_NOEXCEPT { return span_.cend(); }
+
+    constexpr reverse_iterator rbegin() const GSL_NOEXCEPT { return span_.rbegin(); }
+    constexpr reverse_iterator rend() const GSL_NOEXCEPT { return span_.rend(); }
+
+    constexpr const_reverse_iterator crbegin() const GSL_NOEXCEPT { return span_.crbegin(); }
+    constexpr const_reverse_iterator crend() const GSL_NOEXCEPT { return span_.crend(); }
+
+private:
+    static impl_type remove_z(pointer const& sz, std::ptrdiff_t max)
+    {
+        return {sz, details::length_func<element_type>()(sz, max)};
+    }
+
+    template <size_t N>
+    static impl_type remove_z(element_type (&sz)[N])
+    {
+        return remove_z(&sz[0], narrow_cast<std::ptrdiff_t>(N));
+    }
+
+    impl_type span_;
+};
+
+template <std::ptrdiff_t Extent = dynamic_extent>
+using string_span = basic_string_span<char, Extent>;
+
+template <std::ptrdiff_t Extent = dynamic_extent>
+using cstring_span = basic_string_span<const char, Extent>;
+
+template <std::ptrdiff_t Extent = dynamic_extent>
+using wstring_span = basic_string_span<wchar_t, Extent>;
+
+template <std::ptrdiff_t Extent = dynamic_extent>
+using cwstring_span = basic_string_span<const wchar_t, Extent>;
+
+//
+// to_string() allow (explicit) conversions from string_span to string
+//
+#ifndef GSL_MSVC_HAS_TYPE_DEDUCTION_BUG
+
+template <typename CharT, std::ptrdiff_t Extent>
+std::basic_string<typename std::remove_const<CharT>::type>
+to_string(basic_string_span<CharT, Extent> view)
+{
+    return {view.data(), static_cast<size_t>(view.length())};
+}
+
+#else
+
+inline std::string to_string(cstring_span<> view)
+{
+    return {view.data(), static_cast<size_t>(view.length())};
+}
+
+inline std::string to_string(string_span<> view)
+{
+    return {view.data(), static_cast<size_t>(view.length())};
+}
+
+inline std::wstring to_string(cwstring_span<> view)
+{
+    return {view.data(), static_cast<size_t>(view.length())};
+}
+
+inline std::wstring to_string(wstring_span<> view)
+{
+    return {view.data(), static_cast<size_t>(view.length())};
+}
+
+#endif
+
+template <typename CharT,
+	  typename Traits = typename std::char_traits<CharT>,
+	  typename Allocator = std::allocator<CharT>,
+	  typename gCharT,
+	  std::ptrdiff_t Extent>
+std::basic_string<CharT, Traits, Allocator> to_basic_string(basic_string_span<gCharT, Extent> view)
+{
+  return {view.data(), static_cast<size_t>(view.length())};
+}
+
+// zero-terminated string span, used to convert
+// zero-terminated spans to legacy strings
+template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
+class basic_zstring_span
+{
+public:
+    using value_type = CharT;
+    using const_value_type = std::add_const_t<CharT>;
+
+    using pointer = std::add_pointer_t<value_type>;
+    using const_pointer = std::add_pointer_t<const_value_type>;
+
+    using zstring_type = basic_zstring<value_type, Extent>;
+    using const_zstring_type = basic_zstring<const_value_type, Extent>;
+
+    using impl_type = span<value_type, Extent>;
+    using string_span_type = basic_string_span<value_type, Extent>;
+
+    constexpr basic_zstring_span(impl_type s) GSL_NOEXCEPT : span_(s)
+    {
+        // expects a zero-terminated span
+        Expects(s[s.size() - 1] == '\0');
+    }
+
+    // copy
+    constexpr basic_zstring_span(const basic_zstring_span& other) = default;
+
+// move
+#ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+    constexpr basic_zstring_span(basic_zstring_span&& other) = default;
+#else
+    constexpr basic_zstring_span(basic_zstring_span&& other) : span_(std::move(other.span_)) {}
+#endif
+
+    // assign
+    constexpr basic_zstring_span& operator=(const basic_zstring_span& other) = default;
+
+// move assign
+#ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+    constexpr basic_zstring_span& operator=(basic_zstring_span&& other) = default;
+#else
+    constexpr basic_zstring_span& operator=(basic_zstring_span&& other)
+    {
+        span_ = std::move(other.span_);
+        return *this;
+    }
+#endif
+
+    constexpr bool empty() const GSL_NOEXCEPT { return span_.size() == 0; }
+
+    constexpr string_span_type as_string_span() const GSL_NOEXCEPT
+    {
+        auto sz = span_.size();
+        return span_.first(sz <= 0 ? 0 : sz - 1);
+    }
+
+    constexpr string_span_type ensure_z() const GSL_NOEXCEPT { return gsl::ensure_z(span_); }
+
+    constexpr const_zstring_type assume_z() const GSL_NOEXCEPT { return span_.data(); }
+
+private:
+    impl_type span_;
+};
+
+template <std::ptrdiff_t Max = dynamic_extent>
+using zstring_span = basic_zstring_span<char, Max>;
+
+template <std::ptrdiff_t Max = dynamic_extent>
+using wzstring_span = basic_zstring_span<wchar_t, Max>;
+
+template <std::ptrdiff_t Max = dynamic_extent>
+using czstring_span = basic_zstring_span<const char, Max>;
+
+template <std::ptrdiff_t Max = dynamic_extent>
+using cwzstring_span = basic_zstring_span<const wchar_t, Max>;
+
+// operator ==
+template <class CharT, std::ptrdiff_t Extent, class T,
+          class = std::enable_if_t<
+              details::is_basic_string_span<T>::value ||
+              std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>>>::value>>
+bool operator==(const gsl::basic_string_span<CharT, Extent>& one, const T& other) GSL_NOEXCEPT
+{
+    gsl::basic_string_span<std::add_const_t<CharT>> tmp(other);
+#ifdef GSL_MSVC_NO_CPP14_STD_EQUAL
+    return (one.size() == tmp.size()) && std::equal(one.begin(), one.end(), tmp.begin());
+#else
+    return std::equal(one.begin(), one.end(), tmp.begin(), tmp.end());
+#endif
+}
+
+template <class CharT, std::ptrdiff_t Extent, class T,
+          class = std::enable_if_t<
+              !details::is_basic_string_span<T>::value &&
+              std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>>>::value>>
+bool operator==(const T& one, const gsl::basic_string_span<CharT, Extent>& other) GSL_NOEXCEPT
+{
+    gsl::basic_string_span<std::add_const_t<CharT>> tmp(one);
+#ifdef GSL_MSVC_NO_CPP14_STD_EQUAL
+    return (tmp.size() == other.size()) && std::equal(tmp.begin(), tmp.end(), other.begin());
+#else
+    return std::equal(tmp.begin(), tmp.end(), other.begin(), other.end());
+#endif
+}
+
+// operator !=
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator!=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    return !(one == other);
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename Dummy = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator!=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    return !(one == other);
+}
+
+// operator<
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator<(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
+    return std::lexicographical_compare(one.begin(), one.end(), tmp.begin(), tmp.end());
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename Dummy = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
+    return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
+}
+
+#ifndef _MSC_VER
+
+// VS treats temp and const containers as convertible to basic_string_span,
+// so the cases below are already covered by the previous operators
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename Dummy = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator<(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
+    return std::lexicographical_compare(one.begin(), one.end(), tmp.begin(), tmp.end());
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename Dummy = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
+    return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
+}
+#endif
+
+// operator <=
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator<=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    return !(other < one);
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename Dummy = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    return !(other < one);
+}
+
+#ifndef _MSC_VER
+
+// VS treats temp and const containers as convertible to basic_string_span,
+// so the cases below are already covered by the previous operators
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename Dummy = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator<=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    return !(other < one);
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename Dummy = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    return !(other < one);
+}
+#endif
+
+// operator>
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator>(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    return other < one;
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename Dummy = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    return other < one;
+}
+
+#ifndef _MSC_VER
+
+// VS treats temp and const containers as convertible to basic_string_span,
+// so the cases below are already covered by the previous operators
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename Dummy = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator>(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    return other < one;
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename Dummy = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    return other < one;
+}
+#endif
+
+// operator >=
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator>=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    return !(one < other);
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename Dummy = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    return !(one < other);
+}
+
+#ifndef _MSC_VER
+
+// VS treats temp and const containers as convertible to basic_string_span,
+// so the cases below are already covered by the previous operators
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename Dummy = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator>=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
+{
+    return !(one < other);
+}
+
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename Dummy = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
+{
+    return !(one < other);
+}
+#endif
+} // namespace GSL
+
+#undef GSL_NOEXCEPT
+
+#ifdef _MSC_VER
+ #pragma warning(pop)
+
+ #if _MSC_VER < 1910
+  #undef constexpr
+  #pragma pop_macro("constexpr")
+
+  // VS 2013 workarounds
+  #if _MSC_VER <= 1800
+   #undef noexcept
+   #pragma pop_macro("noexcept")
+
+   #undef GSL_MSVC_HAS_TYPE_DEDUCTION_BUG
+   #undef GSL_MSVC_HAS_SFINAE_SUBSTITUTION_ICE
+   #undef GSL_MSVC_NO_CPP14_STD_EQUAL
+   #undef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+  #endif // _MSC_VER <= 1800
+ #endif // _MSC_VER < 1910
+#endif // _MSC_VER
+
+#endif // GSL_STRING_SPAN_H