// Copyright 2017-2020 by Martin Moene
//
// string-view lite, a C++17-like string_view for C++98 and later.
// For more information see https://github.com/martinmoene/string-view-lite
//
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#pragma once

#ifndef NONSTD_SV_LITE_H_INCLUDED
#define NONSTD_SV_LITE_H_INCLUDED

#define string_view_lite_MAJOR 1
#define string_view_lite_MINOR 7
#define string_view_lite_PATCH 0

#define string_view_lite_VERSION                                               \
    nssv_STRINGIFY(string_view_lite_MAJOR) "." nssv_STRINGIFY(                 \
        string_view_lite_MINOR) "." nssv_STRINGIFY(string_view_lite_PATCH)

#define nssv_STRINGIFY(x) nssv_STRINGIFY_(x)
#define nssv_STRINGIFY_(x) #x

// string-view lite configuration:

#define nssv_STRING_VIEW_DEFAULT 0
#define nssv_STRING_VIEW_NONSTD 1
#define nssv_STRING_VIEW_STD 2

// tweak header support:

#ifdef __has_include
#if __has_include(<nonstd/string_view.tweak.hpp>)
#include <nonstd/string_view.tweak.hpp>
#endif
#define nssv_HAVE_TWEAK_HEADER 1
#else
#define nssv_HAVE_TWEAK_HEADER 0
//# pragma message("string_view.hpp: Note: Tweak header not supported.")
#endif

// string_view selection and configuration:

#if !defined(nssv_CONFIG_SELECT_STRING_VIEW)
#define nssv_CONFIG_SELECT_STRING_VIEW                                         \
    (nssv_HAVE_STD_STRING_VIEW ? nssv_STRING_VIEW_STD : nssv_STRING_VIEW_NONSTD)
#endif

#ifndef nssv_CONFIG_STD_SV_OPERATOR
#define nssv_CONFIG_STD_SV_OPERATOR 0
#endif

#ifndef nssv_CONFIG_USR_SV_OPERATOR
#define nssv_CONFIG_USR_SV_OPERATOR 1
#endif

#ifdef nssv_CONFIG_CONVERSION_STD_STRING
#define nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS                        \
    nssv_CONFIG_CONVERSION_STD_STRING
#define nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS                       \
    nssv_CONFIG_CONVERSION_STD_STRING
#endif

#ifndef nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS
#define nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS 1
#endif

#ifndef nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS
#define nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS 1
#endif

#ifndef nssv_CONFIG_NO_STREAM_INSERTION
#define nssv_CONFIG_NO_STREAM_INSERTION 0
#endif

// Control presence of exception handling (try and auto discover):

#ifndef nssv_CONFIG_NO_EXCEPTIONS
#if defined(_MSC_VER)
#include <cstddef>// for _HAS_EXCEPTIONS
#endif
#if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || (_HAS_EXCEPTIONS)
#define nssv_CONFIG_NO_EXCEPTIONS 0
#else
#define nssv_CONFIG_NO_EXCEPTIONS 1
#endif
#endif

// C++ language version detection (C++23 is speculative):
// Note: VC14.0/1900 (VS2015) lacks too much from C++14.

#ifndef nssv_CPLUSPLUS
#if defined(_MSVC_LANG) && !defined(__clang__)
#define nssv_CPLUSPLUS (_MSC_VER == 1900 ? 201103L : _MSVC_LANG)
#else
#define nssv_CPLUSPLUS __cplusplus
#endif
#endif

#define nssv_CPP98_OR_GREATER (nssv_CPLUSPLUS >= 199711L)
#define nssv_CPP11_OR_GREATER (nssv_CPLUSPLUS >= 201103L)
#define nssv_CPP11_OR_GREATER_ (nssv_CPLUSPLUS >= 201103L)
#define nssv_CPP14_OR_GREATER (nssv_CPLUSPLUS >= 201402L)
#define nssv_CPP17_OR_GREATER (nssv_CPLUSPLUS >= 201703L)
#define nssv_CPP20_OR_GREATER (nssv_CPLUSPLUS >= 202002L)
#define nssv_CPP23_OR_GREATER (nssv_CPLUSPLUS >= 202300L)

// use C++17 std::string_view if available and requested:

#if nssv_CPP17_OR_GREATER && defined(__has_include)
#if __has_include(<string_view> )
#define nssv_HAVE_STD_STRING_VIEW 1
#else
#define nssv_HAVE_STD_STRING_VIEW 0
#endif
#else
#define nssv_HAVE_STD_STRING_VIEW 0
#endif

#define nssv_USES_STD_STRING_VIEW                                              \
    ((nssv_CONFIG_SELECT_STRING_VIEW == nssv_STRING_VIEW_STD)                  \
     || ((nssv_CONFIG_SELECT_STRING_VIEW == nssv_STRING_VIEW_DEFAULT)          \
         && nssv_HAVE_STD_STRING_VIEW))

#define nssv_HAVE_STARTS_WITH                                                  \
    (nssv_CPP20_OR_GREATER || !nssv_USES_STD_STRING_VIEW)
#define nssv_HAVE_ENDS_WITH nssv_HAVE_STARTS_WITH

//
// Use C++17 std::string_view:
//

#if nssv_USES_STD_STRING_VIEW

#include <string_view>

// Extensions for std::string:

#if nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

namespace nonstd {

template<class CharT, class Traits, class Allocator = std::allocator<CharT>>
std::basic_string<CharT, Traits, Allocator>
to_string(std::basic_string_view<CharT, Traits> v,
          Allocator const &a = Allocator())
{
    return std::basic_string<CharT, Traits, Allocator>(v.begin(), v.end(), a);
}

template<class CharT, class Traits, class Allocator>
std::basic_string_view<CharT, Traits>
to_string_view(std::basic_string<CharT, Traits, Allocator> const &s)
{
    return std::basic_string_view<CharT, Traits>(s.data(), s.size());
}

// Literal operators sv and _sv:

#if nssv_CONFIG_STD_SV_OPERATOR

using namespace std::literals::string_view_literals;

#endif

#if nssv_CONFIG_USR_SV_OPERATOR

inline namespace literals {
inline namespace string_view_literals {

constexpr std::string_view
operator"" _sv(const char *str, size_t len) noexcept// (1)
{
    return std::string_view{str, len};
}

constexpr std::u16string_view
operator"" _sv(const char16_t *str, size_t len) noexcept// (2)
{
    return std::u16string_view{str, len};
}

constexpr std::u32string_view
operator"" _sv(const char32_t *str, size_t len) noexcept// (3)
{
    return std::u32string_view{str, len};
}

constexpr std::wstring_view
operator"" _sv(const wchar_t *str, size_t len) noexcept// (4)
{
    return std::wstring_view{str, len};
}

}// namespace string_view_literals
}// namespace literals

#endif// nssv_CONFIG_USR_SV_OPERATOR

}// namespace nonstd

#endif// nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

namespace nonstd {

using std::basic_string_view;
using std::string_view;
using std::u16string_view;
using std::u32string_view;
using std::wstring_view;

// literal "sv" and "_sv", see above

using std::operator==;
using std::operator!=;
using std::operator<;
using std::operator<=;
using std::operator>;
using std::operator>=;

using std::operator<<;

}// namespace nonstd

#else// nssv_HAVE_STD_STRING_VIEW

//
// Before C++17: use string_view lite:
//

// Compiler versions:
//
// MSVC++  6.0  _MSC_VER == 1200  nssv_COMPILER_MSVC_VERSION ==  60  (Visual Studio 6.0)
// MSVC++  7.0  _MSC_VER == 1300  nssv_COMPILER_MSVC_VERSION ==  70  (Visual Studio .NET 2002)
// MSVC++  7.1  _MSC_VER == 1310  nssv_COMPILER_MSVC_VERSION ==  71  (Visual Studio .NET 2003)
// MSVC++  8.0  _MSC_VER == 1400  nssv_COMPILER_MSVC_VERSION ==  80  (Visual Studio 2005)
// MSVC++  9.0  _MSC_VER == 1500  nssv_COMPILER_MSVC_VERSION ==  90  (Visual Studio 2008)
// MSVC++ 10.0  _MSC_VER == 1600  nssv_COMPILER_MSVC_VERSION == 100  (Visual Studio 2010)
// MSVC++ 11.0  _MSC_VER == 1700  nssv_COMPILER_MSVC_VERSION == 110  (Visual Studio 2012)
// MSVC++ 12.0  _MSC_VER == 1800  nssv_COMPILER_MSVC_VERSION == 120  (Visual Studio 2013)
// MSVC++ 14.0  _MSC_VER == 1900  nssv_COMPILER_MSVC_VERSION == 140  (Visual Studio 2015)
// MSVC++ 14.1  _MSC_VER >= 1910  nssv_COMPILER_MSVC_VERSION == 141  (Visual Studio 2017)
// MSVC++ 14.2  _MSC_VER >= 1920  nssv_COMPILER_MSVC_VERSION == 142  (Visual Studio 2019)

#if defined(_MSC_VER) && !defined(__clang__)
#define nssv_COMPILER_MSVC_VER (_MSC_VER)
#define nssv_COMPILER_MSVC_VERSION                                             \
    (_MSC_VER / 10 - 10 * (5 + (_MSC_VER < 1900)))
#else
#define nssv_COMPILER_MSVC_VER 0
#define nssv_COMPILER_MSVC_VERSION 0
#endif

#define nssv_COMPILER_VERSION(major, minor, patch)                             \
    (10 * (10 * (major) + (minor)) + (patch))

#if defined(__apple_build_version__)
#define nssv_COMPILER_APPLECLANG_VERSION                                       \
    nssv_COMPILER_VERSION(__clang_major__, __clang_minor__,                    \
                          __clang_patchlevel__)
#define nssv_COMPILER_CLANG_VERSION 0
#elif defined(__clang__)
#define nssv_COMPILER_APPLECLANG_VERSION 0
#define nssv_COMPILER_CLANG_VERSION                                            \
    nssv_COMPILER_VERSION(__clang_major__, __clang_minor__,                    \
                          __clang_patchlevel__)
#else
#define nssv_COMPILER_APPLECLANG_VERSION 0
#define nssv_COMPILER_CLANG_VERSION 0
#endif

#if defined(__GNUC__) && !defined(__clang__)
#define nssv_COMPILER_GNUC_VERSION                                             \
    nssv_COMPILER_VERSION(__GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__)
#else
#define nssv_COMPILER_GNUC_VERSION 0
#endif

// half-open range [lo..hi):
#define nssv_BETWEEN(v, lo, hi) ((lo) <= (v) && (v) < (hi))

// Presence of language and library features:

#ifdef _HAS_CPP0X
#define nssv_HAS_CPP0X _HAS_CPP0X
#else
#define nssv_HAS_CPP0X 0
#endif

// Unless defined otherwise below, consider VC14 as C++11 for variant-lite:

#if nssv_COMPILER_MSVC_VER >= 1900
#undef nssv_CPP11_OR_GREATER
#define nssv_CPP11_OR_GREATER 1
#endif

#define nssv_CPP11_90 (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1500)
#define nssv_CPP11_100                                                         \
    (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1600)
#define nssv_CPP11_110                                                         \
    (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1700)
#define nssv_CPP11_120                                                         \
    (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1800)
#define nssv_CPP11_140                                                         \
    (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1900)
#define nssv_CPP11_141                                                         \
    (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1910)

#define nssv_CPP14_000 (nssv_CPP14_OR_GREATER)
#define nssv_CPP17_000 (nssv_CPP17_OR_GREATER)

// Presence of C++11 language features:

#define nssv_HAVE_CONSTEXPR_11 nssv_CPP11_140
#define nssv_HAVE_EXPLICIT_CONVERSION nssv_CPP11_140
#define nssv_HAVE_INLINE_NAMESPACE nssv_CPP11_140
#define nssv_HAVE_IS_DEFAULT nssv_CPP11_140
#define nssv_HAVE_IS_DELETE nssv_CPP11_140
#define nssv_HAVE_NOEXCEPT nssv_CPP11_140
#define nssv_HAVE_NULLPTR nssv_CPP11_100
#define nssv_HAVE_REF_QUALIFIER nssv_CPP11_140
#define nssv_HAVE_UNICODE_LITERALS nssv_CPP11_140
#define nssv_HAVE_USER_DEFINED_LITERALS nssv_CPP11_140
#define nssv_HAVE_WCHAR16_T nssv_CPP11_100
#define nssv_HAVE_WCHAR32_T nssv_CPP11_100

#if !((nssv_CPP11_OR_GREATER && nssv_COMPILER_CLANG_VERSION)                   \
      || nssv_BETWEEN(nssv_COMPILER_CLANG_VERSION, 300, 400))
#define nssv_HAVE_STD_DEFINED_LITERALS nssv_CPP11_140
#else
#define nssv_HAVE_STD_DEFINED_LITERALS 0
#endif

// Presence of C++14 language features:

#define nssv_HAVE_CONSTEXPR_14 nssv_CPP14_000

// Presence of C++17 language features:

#define nssv_HAVE_NODISCARD nssv_CPP17_000

// Presence of C++ library features:

#define nssv_HAVE_STD_HASH nssv_CPP11_120

// Presence of compiler intrinsics:

// Providing char-type specializations for compare() and length() that
// use compiler intrinsics can improve compile- and run-time performance.
//
// The challenge is in using the right combinations of builtin availability
// and its constexpr-ness.
//
// | compiler | __builtin_memcmp (constexpr) | memcmp  (constexpr) |
// |----------|------------------------------|---------------------|
// | clang    | 4.0              (>= 4.0   ) | any     (?        ) |
// | clang-a  | 9.0              (>= 9.0   ) | any     (?        ) |
// | gcc      | any              (constexpr) | any     (?        ) |
// | msvc     | >= 14.2 C++17    (>= 14.2  ) | any     (?        ) |

#define nssv_HAVE_BUILTIN_VER                                                  \
    ((nssv_CPP17_000 && nssv_COMPILER_MSVC_VERSION >= 142)                     \
     || nssv_COMPILER_GNUC_VERSION > 0 || nssv_COMPILER_CLANG_VERSION >= 400   \
     || nssv_COMPILER_APPLECLANG_VERSION >= 900)
#define nssv_HAVE_BUILTIN_CE (nssv_HAVE_BUILTIN_VER)

#define nssv_HAVE_BUILTIN_MEMCMP                                               \
    ((nssv_HAVE_CONSTEXPR_14 && nssv_HAVE_BUILTIN_CE)                          \
     || !nssv_HAVE_CONSTEXPR_14)
#define nssv_HAVE_BUILTIN_STRLEN                                               \
    ((nssv_HAVE_CONSTEXPR_11 && nssv_HAVE_BUILTIN_CE)                          \
     || !nssv_HAVE_CONSTEXPR_11)

#ifdef __has_builtin
#define nssv_HAVE_BUILTIN(x) __has_builtin(x)
#else
#define nssv_HAVE_BUILTIN(x) 0
#endif

#if nssv_HAVE_BUILTIN(__builtin_memcmp) || nssv_HAVE_BUILTIN_VER
#define nssv_BUILTIN_MEMCMP __builtin_memcmp
#else
#define nssv_BUILTIN_MEMCMP memcmp
#endif

#if nssv_HAVE_BUILTIN(__builtin_strlen) || nssv_HAVE_BUILTIN_VER
#define nssv_BUILTIN_STRLEN __builtin_strlen
#else
#define nssv_BUILTIN_STRLEN strlen
#endif

// C++ feature usage:

#if nssv_HAVE_CONSTEXPR_11
#define nssv_constexpr constexpr
#else
#define nssv_constexpr /*constexpr*/
#endif

#if nssv_HAVE_CONSTEXPR_14
#define nssv_constexpr14 constexpr
#else
#define nssv_constexpr14 /*constexpr*/
#endif

#if nssv_HAVE_EXPLICIT_CONVERSION
#define nssv_explicit explicit
#else
#define nssv_explicit /*explicit*/
#endif

#if nssv_HAVE_INLINE_NAMESPACE
#define nssv_inline_ns inline
#else
#define nssv_inline_ns /*inline*/
#endif

#if nssv_HAVE_NOEXCEPT
#define nssv_noexcept noexcept
#else
#define nssv_noexcept /*noexcept*/
#endif

//#if nssv_HAVE_REF_QUALIFIER
//# define nssv_ref_qual  &
//# define nssv_refref_qual  &&
//#else
//# define nssv_ref_qual  /*&*/
//# define nssv_refref_qual  /*&&*/
//#endif

#if nssv_HAVE_NULLPTR
#define nssv_nullptr nullptr
#else
#define nssv_nullptr NULL
#endif

#if nssv_HAVE_NODISCARD
#define nssv_nodiscard [[nodiscard]]
#else
#define nssv_nodiscard /*[[nodiscard]]*/
#endif

// Additional includes:

#include <algorithm>
#include <cassert>
#include <iterator>
#include <limits>
#include <string>// std::char_traits<>

#if !nssv_CONFIG_NO_STREAM_INSERTION
#include <ostream>
#endif

#if !nssv_CONFIG_NO_EXCEPTIONS
#include <stdexcept>
#endif

#if nssv_CPP11_OR_GREATER
#include <type_traits>
#endif

// Clang, GNUC, MSVC warning suppression macros:

#if defined(__clang__)
#pragma clang diagnostic ignored "-Wreserved-user-defined-literal"
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wuser-defined-literals"
#elif defined(__GNUC__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wliteral-suffix"
#endif// __clang__

#if nssv_COMPILER_MSVC_VERSION >= 140
#define nssv_SUPPRESS_MSGSL_WARNING(expr) [[gsl::suppress(expr)]]
#define nssv_SUPPRESS_MSVC_WARNING(code, descr)                                \
    __pragma(warning(suppress : code))
#define nssv_DISABLE_MSVC_WARNINGS(codes)                                      \
    __pragma(warning(push)) __pragma(warning(disable : codes))
#else
#define nssv_SUPPRESS_MSGSL_WARNING(expr)
#define nssv_SUPPRESS_MSVC_WARNING(code, descr)
#define nssv_DISABLE_MSVC_WARNINGS(codes)
#endif

#if defined(__clang__)
#define nssv_RESTORE_WARNINGS() _Pragma("clang diagnostic pop")
#elif defined(__GNUC__)
#define nssv_RESTORE_WARNINGS() _Pragma("GCC diagnostic pop")
#elif nssv_COMPILER_MSVC_VERSION >= 140
#define nssv_RESTORE_WARNINGS() __pragma(warning(pop))
#else
#define nssv_RESTORE_WARNINGS()
#endif

// Suppress the following MSVC (GSL) warnings:
// - C4455, non-gsl   : 'operator ""sv': literal suffix identifiers that do not
//                      start with an underscore are reserved
// - C26472, gsl::t.1 : don't use a static_cast for arithmetic conversions;
//                      use brace initialization, gsl::narrow_cast or gsl::narow
// - C26481: gsl::b.1 : don't use pointer arithmetic. Use span instead

nssv_DISABLE_MSVC_WARNINGS(4455 26481 26472)
    //nssv_DISABLE_CLANG_WARNINGS( "-Wuser-defined-literals" )
    //nssv_DISABLE_GNUC_WARNINGS( -Wliteral-suffix )

    namespace nonstd
{
    namespace sv_lite {

    //
    // basic_string_view declaration:
    //

    template<class CharT, class Traits = std::char_traits<CharT>>
    class basic_string_view;

    namespace detail {

    // support constexpr comparison in C++14;
    // for C++17 and later, use provided traits:

    template<typename CharT>
    inline nssv_constexpr14 int
    compare(CharT const *s1, CharT const *s2, std::size_t count)
    {
        while (count-- != 0) {
            if (*s1 < *s2) return -1;
            if (*s1 > *s2) return +1;
            ++s1;
            ++s2;
        }
        return 0;
    }

#if nssv_HAVE_BUILTIN_MEMCMP

    // specialization of compare() for char, see also generic compare() above:

    inline nssv_constexpr14 int
    compare(char const *s1, char const *s2, std::size_t count)
    {
        return nssv_BUILTIN_MEMCMP(s1, s2, count);
    }

#endif

#if nssv_HAVE_BUILTIN_STRLEN

    // specialization of length() for char, see also generic length() further below:

    inline nssv_constexpr std::size_t length(char const *s)
    {
        return nssv_BUILTIN_STRLEN(s);
    }

#endif

#if defined(__OPTIMIZE__)

    // gcc, clang provide __OPTIMIZE__
    // Expect tail call optimization to make length() non-recursive:

    template<typename CharT>
    inline nssv_constexpr std::size_t length(CharT *s, std::size_t result = 0)
    {
        return *s == '\0' ? result : length(s + 1, result + 1);
    }

#else// OPTIMIZE

    // non-recursive:

    template<typename CharT>
    inline nssv_constexpr14 std::size_t length(CharT *s)
    {
        std::size_t result = 0;
        while (*s++ != '\0') { ++result; }
        return result;
    }

#endif// OPTIMIZE

#if nssv_CPP11_OR_GREATER && !nssv_CPP17_OR_GREATER
#if defined(__OPTIMIZE__)

    // gcc, clang provide __OPTIMIZE__
    // Expect tail call optimization to make search() non-recursive:

    template<class CharT, class Traits = std::char_traits<CharT>>
    constexpr const CharT *search(basic_string_view<CharT, Traits> haystack,
                                  basic_string_view<CharT, Traits> needle)
    {
        return haystack.starts_with(needle) ? haystack.begin()
            : haystack.empty()              ? haystack.end()
                               : search(haystack.substr(1), needle);
    }

#else// OPTIMIZE

    // non-recursive:

    template<class CharT, class Traits = std::char_traits<CharT>>
    constexpr const CharT *search(basic_string_view<CharT, Traits> haystack,
                                  basic_string_view<CharT, Traits> needle)
    {
        return std::search(haystack.begin(), haystack.end(), needle.begin(),
                           needle.end());
    }

#endif// OPTIMIZE
#endif// nssv_CPP11_OR_GREATER && ! nssv_CPP17_OR_GREATER

    }// namespace detail

    //
    // basic_string_view:
    //

    template<class CharT, class Traits /* = std::char_traits<CharT> */
             >
    class basic_string_view {
    public:
        // Member types:

        typedef Traits traits_type;
        typedef CharT value_type;

        typedef CharT *pointer;
        typedef CharT const *const_pointer;
        typedef CharT &reference;
        typedef CharT const &const_reference;

        typedef const_pointer iterator;
        typedef const_pointer const_iterator;
        typedef std::reverse_iterator<const_iterator> reverse_iterator;
        typedef std::reverse_iterator<const_iterator> const_reverse_iterator;

        typedef std::size_t size_type;
        typedef std::ptrdiff_t difference_type;

        // 24.4.2.1 Construction and assignment:

        nssv_constexpr basic_string_view() nssv_noexcept : data_(nssv_nullptr),
                                                           size_(0)
        {}

#if nssv_CPP11_OR_GREATER
        nssv_constexpr basic_string_view(basic_string_view const &other)
            nssv_noexcept = default;
#else
        nssv_constexpr
        basic_string_view(basic_string_view const &other) nssv_noexcept
            : data_(other.data_),
              size_(other.size_)
        {}
#endif

        nssv_constexpr basic_string_view(CharT const *s, size_type count)
            nssv_noexcept// non-standard noexcept
            : data_(s),
              size_(count)
        {}

        nssv_constexpr
        basic_string_view(CharT const *s) nssv_noexcept// non-standard noexcept
            : data_(s)
#if nssv_CPP17_OR_GREATER
            ,
              size_(Traits::length(s))
#elif nssv_CPP11_OR_GREATER
            ,
              size_(detail::length(s))
#else
            ,
              size_(Traits::length(s))
#endif
        {}

#if nssv_HAVE_NULLPTR
#if nssv_HAVE_IS_DELETE
        nssv_constexpr basic_string_view(std::nullptr_t) nssv_noexcept = delete;
#else
    private:
        nssv_constexpr basic_string_view(std::nullptr_t) nssv_noexcept;

    public:
#endif
#endif

        // Assignment:

#if nssv_CPP11_OR_GREATER
        nssv_constexpr14 basic_string_view &
        operator=(basic_string_view const &other) nssv_noexcept = default;
#else
        nssv_constexpr14 basic_string_view &
        operator=(basic_string_view const &other) nssv_noexcept
        {
            data_ = other.data_;
            size_ = other.size_;
            return *this;
        }
#endif

        // 24.4.2.2 Iterator support:

        nssv_constexpr const_iterator begin() const nssv_noexcept
        {
            return data_;
        }

        nssv_constexpr const_iterator end() const nssv_noexcept
        {
            return data_ + size_;
        }

        nssv_constexpr const_iterator cbegin() const nssv_noexcept
        {
            return begin();
        }

        nssv_constexpr const_iterator cend() const nssv_noexcept
        {
            return end();
        }

        nssv_constexpr const_reverse_iterator rbegin() const nssv_noexcept
        {
            return const_reverse_iterator(end());
        }

        nssv_constexpr const_reverse_iterator rend() const nssv_noexcept
        {
            return const_reverse_iterator(begin());
        }

        nssv_constexpr const_reverse_iterator crbegin() const nssv_noexcept
        {
            return rbegin();
        }

        nssv_constexpr const_reverse_iterator crend() const nssv_noexcept
        {
            return rend();
        }

        // 24.4.2.3 Capacity:

        nssv_constexpr size_type size() const nssv_noexcept { return size_; }

        nssv_constexpr size_type length() const nssv_noexcept { return size_; }

        nssv_constexpr size_type max_size() const nssv_noexcept
        {
            return (std::numeric_limits<size_type>::max)();
        }

        // since C++20
        nssv_nodiscard nssv_constexpr bool empty() const nssv_noexcept
        {
            return 0 == size_;
        }

        // 24.4.2.4 Element access:

        nssv_constexpr const_reference operator[](size_type pos) const
        {
            return data_at(pos);
        }

        nssv_constexpr14 const_reference at(size_type pos) const
        {
#if nssv_CONFIG_NO_EXCEPTIONS
            assert(pos < size());
#else
            if (pos >= size()) {
                throw std::out_of_range("nonstd::string_view::at()");
            }
#endif
            return data_at(pos);
        }

        nssv_constexpr const_reference front() const { return data_at(0); }

        nssv_constexpr const_reference back() const
        {
            return data_at(size() - 1);
        }

        nssv_constexpr const_pointer data() const nssv_noexcept
        {
            return data_;
        }

        // 24.4.2.5 Modifiers:

        nssv_constexpr14 void remove_prefix(size_type n)
        {
            assert(n <= size());
            data_ += n;
            size_ -= n;
        }

        nssv_constexpr14 void remove_suffix(size_type n)
        {
            assert(n <= size());
            size_ -= n;
        }

        nssv_constexpr14 void swap(basic_string_view &other) nssv_noexcept
        {
            const basic_string_view tmp(other);
            other = *this;
            *this = tmp;
        }

        // 24.4.2.6 String operations:

        size_type copy(CharT *dest, size_type n, size_type pos = 0) const
        {
#if nssv_CONFIG_NO_EXCEPTIONS
            assert(pos <= size());
#else
            if (pos > size()) {
                throw std::out_of_range("nonstd::string_view::copy()");
            }
#endif
            const size_type rlen = (std::min)(n, size() - pos);

            (void) Traits::copy(dest, data() + pos, rlen);

            return rlen;
        }

        nssv_constexpr14 basic_string_view substr(size_type pos = 0,
                                                  size_type n = npos) const
        {
#if nssv_CONFIG_NO_EXCEPTIONS
            assert(pos <= size());
#else
            if (pos > size()) {
                throw std::out_of_range("nonstd::string_view::substr()");
            }
#endif
            return basic_string_view(data() + pos, (std::min)(n, size() - pos));
        }

        // compare(), 6x:

        nssv_constexpr14 int
        compare(basic_string_view other) const nssv_noexcept// (1)
        {
#if nssv_CPP17_OR_GREATER
            if (const int result = Traits::compare(
                    data(), other.data(), (std::min)(size(), other.size())))
#else
            if (const int result = detail::compare(
                    data(), other.data(), (std::min)(size(), other.size())))
#endif
            {
                return result;
            }

            return size() == other.size() ? 0 : size() < other.size() ? -1 : 1;
        }

        nssv_constexpr int compare(size_type pos1,
                                   size_type n1,
                                   basic_string_view other) const// (2)
        {
            return substr(pos1, n1).compare(other);
        }

        nssv_constexpr int compare(size_type pos1,
                                   size_type n1,
                                   basic_string_view other,
                                   size_type pos2,
                                   size_type n2) const// (3)
        {
            return substr(pos1, n1).compare(other.substr(pos2, n2));
        }

        nssv_constexpr int compare(CharT const *s) const// (4)
        {
            return compare(basic_string_view(s));
        }

        nssv_constexpr int
        compare(size_type pos1, size_type n1, CharT const *s) const// (5)
        {
            return substr(pos1, n1).compare(basic_string_view(s));
        }

        nssv_constexpr int compare(size_type pos1,
                                   size_type n1,
                                   CharT const *s,
                                   size_type n2) const// (6)
        {
            return substr(pos1, n1).compare(basic_string_view(s, n2));
        }

        // 24.4.2.7 Searching:

        // starts_with(), 3x, since C++20:

        nssv_constexpr bool
        starts_with(basic_string_view v) const nssv_noexcept// (1)
        {
            return size() >= v.size() && compare(0, v.size(), v) == 0;
        }

        nssv_constexpr bool starts_with(CharT c) const nssv_noexcept// (2)
        {
            return starts_with(basic_string_view(&c, 1));
        }

        nssv_constexpr bool starts_with(CharT const *s) const// (3)
        {
            return starts_with(basic_string_view(s));
        }

        // ends_with(), 3x, since C++20:

        nssv_constexpr bool
        ends_with(basic_string_view v) const nssv_noexcept// (1)
        {
            return size() >= v.size()
                && compare(size() - v.size(), npos, v) == 0;
        }

        nssv_constexpr bool ends_with(CharT c) const nssv_noexcept// (2)
        {
            return ends_with(basic_string_view(&c, 1));
        }

        nssv_constexpr bool ends_with(CharT const *s) const// (3)
        {
            return ends_with(basic_string_view(s));
        }

        // find(), 4x:

        nssv_constexpr size_type
        find(basic_string_view v, size_type pos = 0) const nssv_noexcept// (1)
        {
            return assert(v.size() == 0 || v.data() != nssv_nullptr),
                   pos >= size() ? npos
                                 : to_pos(
#if nssv_CPP11_OR_GREATER && !nssv_CPP17_OR_GREATER
                                     detail::search(substr(pos), v)
#else
                                     std::search(cbegin() + pos, cend(),
                                                 v.cbegin(), v.cend(),
                                                 Traits::eq)
#endif
                                 );
        }

        nssv_constexpr size_type
        find(CharT c, size_type pos = 0) const nssv_noexcept// (2)
        {
            return find(basic_string_view(&c, 1), pos);
        }

        nssv_constexpr size_type find(CharT const *s,
                                      size_type pos,
                                      size_type n) const// (3)
        {
            return find(basic_string_view(s, n), pos);
        }

        nssv_constexpr size_type find(CharT const *s,
                                      size_type pos = 0) const// (4)
        {
            return find(basic_string_view(s), pos);
        }

        // rfind(), 4x:

        nssv_constexpr14 size_type
        rfind(basic_string_view v,
              size_type pos = npos) const nssv_noexcept// (1)
        {
            if (size() < v.size()) { return npos; }

            if (v.empty()) { return (std::min)(size(), pos); }

            const_iterator last =
                cbegin() + (std::min)(size() - v.size(), pos) + v.size();
            const_iterator result =
                std::find_end(cbegin(), last, v.cbegin(), v.cend(), Traits::eq);

            return result != last ? size_type(result - cbegin()) : npos;
        }

        nssv_constexpr14 size_type
        rfind(CharT c, size_type pos = npos) const nssv_noexcept// (2)
        {
            return rfind(basic_string_view(&c, 1), pos);
        }

        nssv_constexpr14 size_type rfind(CharT const *s,
                                         size_type pos,
                                         size_type n) const// (3)
        {
            return rfind(basic_string_view(s, n), pos);
        }

        nssv_constexpr14 size_type rfind(CharT const *s,
                                         size_type pos = npos) const// (4)
        {
            return rfind(basic_string_view(s), pos);
        }

        // find_first_of(), 4x:

        nssv_constexpr size_type
        find_first_of(basic_string_view v,
                      size_type pos = 0) const nssv_noexcept// (1)
        {
            return pos >= size()
                ? npos
                : to_pos(std::find_first_of(cbegin() + pos, cend(), v.cbegin(),
                                            v.cend(), Traits::eq));
        }

        nssv_constexpr size_type
        find_first_of(CharT c, size_type pos = 0) const nssv_noexcept// (2)
        {
            return find_first_of(basic_string_view(&c, 1), pos);
        }

        nssv_constexpr size_type find_first_of(CharT const *s,
                                               size_type pos,
                                               size_type n) const// (3)
        {
            return find_first_of(basic_string_view(s, n), pos);
        }

        nssv_constexpr size_type find_first_of(CharT const *s,
                                               size_type pos = 0) const// (4)
        {
            return find_first_of(basic_string_view(s), pos);
        }

        // find_last_of(), 4x:

        nssv_constexpr size_type
        find_last_of(basic_string_view v,
                     size_type pos = npos) const nssv_noexcept// (1)
        {
            return empty()      ? npos
                : pos >= size() ? find_last_of(v, size() - 1)
                                : to_pos(std::find_first_of(
                                    const_reverse_iterator(cbegin() + pos + 1),
                                    crend(), v.cbegin(), v.cend(), Traits::eq));
        }

        nssv_constexpr size_type
        find_last_of(CharT c, size_type pos = npos) const nssv_noexcept// (2)
        {
            return find_last_of(basic_string_view(&c, 1), pos);
        }

        nssv_constexpr size_type find_last_of(CharT const *s,
                                              size_type pos,
                                              size_type count) const// (3)
        {
            return find_last_of(basic_string_view(s, count), pos);
        }

        nssv_constexpr size_type find_last_of(CharT const *s,
                                              size_type pos = npos) const// (4)
        {
            return find_last_of(basic_string_view(s), pos);
        }

        // find_first_not_of(), 4x:

        nssv_constexpr size_type
        find_first_not_of(basic_string_view v,
                          size_type pos = 0) const nssv_noexcept// (1)
        {
            return pos >= size()
                ? npos
                : to_pos(std::find_if(cbegin() + pos, cend(), not_in_view(v)));
        }

        nssv_constexpr size_type
        find_first_not_of(CharT c, size_type pos = 0) const nssv_noexcept// (2)
        {
            return find_first_not_of(basic_string_view(&c, 1), pos);
        }

        nssv_constexpr size_type find_first_not_of(CharT const *s,
                                                   size_type pos,
                                                   size_type count) const// (3)
        {
            return find_first_not_of(basic_string_view(s, count), pos);
        }

        nssv_constexpr size_type
        find_first_not_of(CharT const *s, size_type pos = 0) const// (4)
        {
            return find_first_not_of(basic_string_view(s), pos);
        }

        // find_last_not_of(), 4x:

        nssv_constexpr size_type
        find_last_not_of(basic_string_view v,
                         size_type pos = npos) const nssv_noexcept// (1)
        {
            return empty()      ? npos
                : pos >= size() ? find_last_not_of(v, size() - 1)
                                : to_pos(std::find_if(
                                    const_reverse_iterator(cbegin() + pos + 1),
                                    crend(), not_in_view(v)));
        }

        nssv_constexpr size_type find_last_not_of(CharT c, size_type pos = npos)
            const nssv_noexcept// (2)
        {
            return find_last_not_of(basic_string_view(&c, 1), pos);
        }

        nssv_constexpr size_type find_last_not_of(CharT const *s,
                                                  size_type pos,
                                                  size_type count) const// (3)
        {
            return find_last_not_of(basic_string_view(s, count), pos);
        }

        nssv_constexpr size_type
        find_last_not_of(CharT const *s, size_type pos = npos) const// (4)
        {
            return find_last_not_of(basic_string_view(s), pos);
        }

        // Constants:

#if nssv_CPP17_OR_GREATER
        static nssv_constexpr size_type npos = size_type(-1);
#elif nssv_CPP11_OR_GREATER
        enum : size_type { npos = size_type(-1) };
#else
        enum { npos = size_type(-1) };
#endif

    private:
        struct not_in_view {
            const basic_string_view v;

            nssv_constexpr explicit not_in_view(basic_string_view v_) : v(v_) {}

            nssv_constexpr bool operator()(CharT c) const
            {
                return npos == v.find_first_of(c);
            }
        };

        nssv_constexpr size_type to_pos(const_iterator it) const
        {
            return it == cend() ? npos : size_type(it - cbegin());
        }

        nssv_constexpr size_type to_pos(const_reverse_iterator it) const
        {
            return it == crend() ? npos : size_type(crend() - it - 1);
        }

        nssv_constexpr const_reference data_at(size_type pos) const
        {
#if nssv_BETWEEN(nssv_COMPILER_GNUC_VERSION, 1, 500)
            return data_[pos];
#else
            return assert(pos < size()), data_[pos];
#endif
        }

    private:
        const_pointer data_;
        size_type size_;

    public:
#if nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS

        template<class Allocator>
        basic_string_view(std::basic_string<CharT, Traits, Allocator> const &s)
            nssv_noexcept : data_(s.data()),
                            size_(s.size())
        {}

#if nssv_HAVE_EXPLICIT_CONVERSION

        template<class Allocator>
        explicit operator std::basic_string<CharT, Traits, Allocator>() const
        {
            return to_string(Allocator());
        }

#endif// nssv_HAVE_EXPLICIT_CONVERSION

#if nssv_CPP11_OR_GREATER

        template<class Allocator = std::allocator<CharT>>
        std::basic_string<CharT, Traits, Allocator>
        to_string(Allocator const &a = Allocator()) const
        {
            return std::basic_string<CharT, Traits, Allocator>(begin(), end(),
                                                               a);
        }

#else

        std::basic_string<CharT, Traits> to_string() const
        {
            return std::basic_string<CharT, Traits>(begin(), end());
        }

        template<class Allocator>
        std::basic_string<CharT, Traits, Allocator>
        to_string(Allocator const &a) const
        {
            return std::basic_string<CharT, Traits, Allocator>(begin(), end(),
                                                               a);
        }

#endif// nssv_CPP11_OR_GREATER

#endif// nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS
    };

    //
    // Non-member functions:
    //

    // 24.4.3 Non-member comparison functions:
    // lexicographically compare two string views (function template):

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator==(basic_string_view<CharT, Traits> lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.size() == rhs.size() && lhs.compare(rhs) == 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator!=(basic_string_view<CharT, Traits> lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return !(lhs == rhs);
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator<(basic_string_view<CharT, Traits> lhs,
              basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) < 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator<=(basic_string_view<CharT, Traits> lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) <= 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator>(basic_string_view<CharT, Traits> lhs,
              basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) > 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator>=(basic_string_view<CharT, Traits> lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) >= 0;
    }

    // Let S be basic_string_view<CharT, Traits>, and sv be an instance of S.
    // Implementations shall provide sufficient additional overloads marked
    // constexpr and noexcept so that an object t with an implicit conversion
    // to S can be compared according to Table 67.

#if !nssv_CPP11_OR_GREATER || nssv_BETWEEN(nssv_COMPILER_MSVC_VERSION, 100, 141)

    // accommodate for older compilers:

    // ==

    template<class CharT, class Traits>
    nssv_constexpr bool operator==(basic_string_view<CharT, Traits> lhs,
                                   CharT const *rhs) nssv_noexcept
    {
        return lhs.size() == detail::length(rhs) && lhs.compare(rhs) == 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator==(CharT const *lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return detail::length(lhs) == rhs.size() && rhs.compare(lhs) == 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator==(basic_string_view<CharT, Traits> lhs,
               std::basic_string<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.size() == rhs.size() && lhs.compare(rhs) == 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator==(std::basic_string<CharT, Traits> rhs,
               basic_string_view<CharT, Traits> lhs) nssv_noexcept
    {
        return lhs.size() == rhs.size() && lhs.compare(rhs) == 0;
    }

    // !=

    template<class CharT, class Traits>
    nssv_constexpr bool operator!=(basic_string_view<CharT, Traits> lhs,
                                   CharT const *rhs) nssv_noexcept
    {
        return !(lhs == rhs);
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator!=(CharT const *lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return !(lhs == rhs);
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator!=(basic_string_view<CharT, Traits> lhs,
               std::basic_string<CharT, Traits> rhs) nssv_noexcept
    {
        return !(lhs == rhs);
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator!=(std::basic_string<CharT, Traits> rhs,
               basic_string_view<CharT, Traits> lhs) nssv_noexcept
    {
        return !(lhs == rhs);
    }

    // <

    template<class CharT, class Traits>
    nssv_constexpr bool operator<(basic_string_view<CharT, Traits> lhs,
                                  CharT const *rhs) nssv_noexcept
    {
        return lhs.compare(rhs) < 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator<(CharT const *lhs,
              basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return rhs.compare(lhs) > 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator<(basic_string_view<CharT, Traits> lhs,
              std::basic_string<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) < 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator<(std::basic_string<CharT, Traits> rhs,
              basic_string_view<CharT, Traits> lhs) nssv_noexcept
    {
        return rhs.compare(lhs) > 0;
    }

    // <=

    template<class CharT, class Traits>
    nssv_constexpr bool operator<=(basic_string_view<CharT, Traits> lhs,
                                   CharT const *rhs) nssv_noexcept
    {
        return lhs.compare(rhs) <= 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator<=(CharT const *lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return rhs.compare(lhs) >= 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator<=(basic_string_view<CharT, Traits> lhs,
               std::basic_string<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) <= 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator<=(std::basic_string<CharT, Traits> rhs,
               basic_string_view<CharT, Traits> lhs) nssv_noexcept
    {
        return rhs.compare(lhs) >= 0;
    }

    // >

    template<class CharT, class Traits>
    nssv_constexpr bool operator>(basic_string_view<CharT, Traits> lhs,
                                  CharT const *rhs) nssv_noexcept
    {
        return lhs.compare(rhs) > 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator>(CharT const *lhs,
              basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return rhs.compare(lhs) < 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator>(basic_string_view<CharT, Traits> lhs,
              std::basic_string<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) > 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator>(std::basic_string<CharT, Traits> rhs,
              basic_string_view<CharT, Traits> lhs) nssv_noexcept
    {
        return rhs.compare(lhs) < 0;
    }

    // >=

    template<class CharT, class Traits>
    nssv_constexpr bool operator>=(basic_string_view<CharT, Traits> lhs,
                                   CharT const *rhs) nssv_noexcept
    {
        return lhs.compare(rhs) >= 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator>=(CharT const *lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return rhs.compare(lhs) <= 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator>=(basic_string_view<CharT, Traits> lhs,
               std::basic_string<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) >= 0;
    }

    template<class CharT, class Traits>
    nssv_constexpr bool
    operator>=(std::basic_string<CharT, Traits> rhs,
               basic_string_view<CharT, Traits> lhs) nssv_noexcept
    {
        return rhs.compare(lhs) <= 0;
    }

#else// newer compilers:

#define nssv_BASIC_STRING_VIEW_I(T, U)                                         \
    typename std::decay<basic_string_view<T, U>>::type

#if defined(_MSC_VER)// issue 40
#define nssv_MSVC_ORDER(x) , int = x
#else
#define nssv_MSVC_ORDER(x) /*, int=x*/
#endif

    // ==

    template<class CharT, class Traits nssv_MSVC_ORDER(1)>
    nssv_constexpr bool operator==(basic_string_view<CharT, Traits> lhs,
                                   nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                       rhs) nssv_noexcept
    {
        return lhs.size() == rhs.size() && lhs.compare(rhs) == 0;
    }

    template<class CharT, class Traits nssv_MSVC_ORDER(2)>
    nssv_constexpr bool
    operator==(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.size() == rhs.size() && lhs.compare(rhs) == 0;
    }

    // !=

    template<class CharT, class Traits nssv_MSVC_ORDER(1)>
    nssv_constexpr bool operator!=(basic_string_view<CharT, Traits> lhs,
                                   nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                       rhs) nssv_noexcept
    {
        return !(lhs == rhs);
    }

    template<class CharT, class Traits nssv_MSVC_ORDER(2)>
    nssv_constexpr bool
    operator!=(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return !(lhs == rhs);
    }

    // <

    template<class CharT, class Traits nssv_MSVC_ORDER(1)>
    nssv_constexpr bool operator<(basic_string_view<CharT, Traits> lhs,
                                  nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                      rhs) nssv_noexcept
    {
        return lhs.compare(rhs) < 0;
    }

    template<class CharT, class Traits nssv_MSVC_ORDER(2)>
    nssv_constexpr bool
    operator<(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
              basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) < 0;
    }

    // <=

    template<class CharT, class Traits nssv_MSVC_ORDER(1)>
    nssv_constexpr bool operator<=(basic_string_view<CharT, Traits> lhs,
                                   nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                       rhs) nssv_noexcept
    {
        return lhs.compare(rhs) <= 0;
    }

    template<class CharT, class Traits nssv_MSVC_ORDER(2)>
    nssv_constexpr bool
    operator<=(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) <= 0;
    }

    // >

    template<class CharT, class Traits nssv_MSVC_ORDER(1)>
    nssv_constexpr bool operator>(basic_string_view<CharT, Traits> lhs,
                                  nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                      rhs) nssv_noexcept
    {
        return lhs.compare(rhs) > 0;
    }

    template<class CharT, class Traits nssv_MSVC_ORDER(2)>
    nssv_constexpr bool
    operator>(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
              basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) > 0;
    }

    // >=

    template<class CharT, class Traits nssv_MSVC_ORDER(1)>
    nssv_constexpr bool operator>=(basic_string_view<CharT, Traits> lhs,
                                   nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                       rhs) nssv_noexcept
    {
        return lhs.compare(rhs) >= 0;
    }

    template<class CharT, class Traits nssv_MSVC_ORDER(2)>
    nssv_constexpr bool
    operator>=(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
               basic_string_view<CharT, Traits> rhs) nssv_noexcept
    {
        return lhs.compare(rhs) >= 0;
    }

#undef nssv_MSVC_ORDER
#undef nssv_BASIC_STRING_VIEW_I

#endif// compiler-dependent approach to comparisons

    // 24.4.4 Inserters and extractors:

#if !nssv_CONFIG_NO_STREAM_INSERTION

    namespace detail {

    template<class Stream>
    void write_padding(Stream &os, std::streamsize n)
    {
        for (std::streamsize i = 0; i < n; ++i) os.rdbuf()->sputc(os.fill());
    }

    template<class Stream, class View>
    Stream &write_to_stream(Stream &os, View const &sv)
    {
        typename Stream::sentry sentry(os);

        if (!sentry) return os;

        const std::streamsize length =
            static_cast<std::streamsize>(sv.length());

        // Whether, and how, to pad:
        const bool pad = (length < os.width());
        const bool left_pad = pad
            && (os.flags() & std::ios_base::adjustfield)
                == std::ios_base::right;

        if (left_pad) write_padding(os, os.width() - length);

        // Write span characters:
        os.rdbuf()->sputn(sv.begin(), length);

        if (pad && !left_pad) write_padding(os, os.width() - length);

        // Reset output stream width:
        os.width(0);

        return os;
    }

    }// namespace detail

    template<class CharT, class Traits>
    std::basic_ostream<CharT, Traits> &
    operator<<(std::basic_ostream<CharT, Traits> &os,
               basic_string_view<CharT, Traits> sv)
    {
        return detail::write_to_stream(os, sv);
    }

#endif// nssv_CONFIG_NO_STREAM_INSERTION

    // Several typedefs for common character types are provided:

    typedef basic_string_view<char> string_view;
    typedef basic_string_view<wchar_t> wstring_view;
#if nssv_HAVE_WCHAR16_T
    typedef basic_string_view<char16_t> u16string_view;
    typedef basic_string_view<char32_t> u32string_view;
#endif

    }// namespace sv_lite
}// namespace nonstd::sv_lite

//
// 24.4.6 Suffix for basic_string_view literals:
//

#if nssv_HAVE_USER_DEFINED_LITERALS

namespace nonstd {
nssv_inline_ns namespace literals
{
    nssv_inline_ns namespace string_view_literals
    {

#if nssv_CONFIG_STD_SV_OPERATOR && nssv_HAVE_STD_DEFINED_LITERALS

        nssv_constexpr nonstd::sv_lite::string_view operator"" sv(
            const char *str, size_t len) nssv_noexcept// (1)
        {
            return nonstd::sv_lite::string_view{str, len};
        }

        nssv_constexpr nonstd::sv_lite::u16string_view operator"" sv(
            const char16_t *str, size_t len) nssv_noexcept// (2)
        {
            return nonstd::sv_lite::u16string_view{str, len};
        }

        nssv_constexpr nonstd::sv_lite::u32string_view operator"" sv(
            const char32_t *str, size_t len) nssv_noexcept// (3)
        {
            return nonstd::sv_lite::u32string_view{str, len};
        }

        nssv_constexpr nonstd::sv_lite::wstring_view operator"" sv(
            const wchar_t *str, size_t len) nssv_noexcept// (4)
        {
            return nonstd::sv_lite::wstring_view{str, len};
        }

#endif// nssv_CONFIG_STD_SV_OPERATOR && nssv_HAVE_STD_DEFINED_LITERALS

#if nssv_CONFIG_USR_SV_OPERATOR

        nssv_constexpr nonstd::sv_lite::string_view operator"" _sv(
            const char *str, size_t len) nssv_noexcept// (1)
        {
            return nonstd::sv_lite::string_view{str, len};
        }

        nssv_constexpr nonstd::sv_lite::u16string_view operator"" _sv(
            const char16_t *str, size_t len) nssv_noexcept// (2)
        {
            return nonstd::sv_lite::u16string_view{str, len};
        }

        nssv_constexpr nonstd::sv_lite::u32string_view operator"" _sv(
            const char32_t *str, size_t len) nssv_noexcept// (3)
        {
            return nonstd::sv_lite::u32string_view{str, len};
        }

        nssv_constexpr nonstd::sv_lite::wstring_view operator"" _sv(
            const wchar_t *str, size_t len) nssv_noexcept// (4)
        {
            return nonstd::sv_lite::wstring_view{str, len};
        }

#endif// nssv_CONFIG_USR_SV_OPERATOR
    }
}
}// namespace nonstd

#endif

//
// Extensions for std::string:
//

#if nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

namespace nonstd {
namespace sv_lite {

// Exclude MSVC 14 (19.00): it yields ambiguous to_string():

#if nssv_CPP11_OR_GREATER && nssv_COMPILER_MSVC_VERSION != 140

template<class CharT, class Traits, class Allocator = std::allocator<CharT>>
std::basic_string<CharT, Traits, Allocator>
to_string(basic_string_view<CharT, Traits> v, Allocator const &a = Allocator())
{
    return std::basic_string<CharT, Traits, Allocator>(v.begin(), v.end(), a);
}

#else

template<class CharT, class Traits>
std::basic_string<CharT, Traits>
to_string(basic_string_view<CharT, Traits> v)
{
    return std::basic_string<CharT, Traits>(v.begin(), v.end());
}

template<class CharT, class Traits, class Allocator>
std::basic_string<CharT, Traits, Allocator>
to_string(basic_string_view<CharT, Traits> v, Allocator const &a)
{
    return std::basic_string<CharT, Traits, Allocator>(v.begin(), v.end(), a);
}

#endif// nssv_CPP11_OR_GREATER

template<class CharT, class Traits, class Allocator>
basic_string_view<CharT, Traits>
to_string_view(std::basic_string<CharT, Traits, Allocator> const &s)
{
    return basic_string_view<CharT, Traits>(s.data(), s.size());
}

}// namespace sv_lite
}// namespace nonstd

#endif// nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

//
// make types and algorithms available in namespace nonstd:
//

namespace nonstd {

using sv_lite::basic_string_view;
using sv_lite::string_view;
using sv_lite::wstring_view;

#if nssv_HAVE_WCHAR16_T
using sv_lite::u16string_view;
#endif
#if nssv_HAVE_WCHAR32_T
using sv_lite::u32string_view;
#endif

// literal "sv"

using sv_lite::operator==;
using sv_lite::operator!=;
using sv_lite::operator<;
using sv_lite::operator<=;
using sv_lite::operator>;
using sv_lite::operator>=;

#if !nssv_CONFIG_NO_STREAM_INSERTION
using sv_lite::operator<<;
#endif

#if nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS
using sv_lite::to_string;
using sv_lite::to_string_view;
#endif

}// namespace nonstd

// 24.4.5 Hash support (C++11):

// Note: The hash value of a string view object is equal to the hash value of
// the corresponding string object.

#if nssv_HAVE_STD_HASH

#include <functional>

namespace std {

template<>
struct hash<nonstd::string_view> {
public:
    std::size_t operator()(nonstd::string_view v) const nssv_noexcept
    {
        return std::hash<std::string>()(std::string(v.data(), v.size()));
    }
};

template<>
struct hash<nonstd::wstring_view> {
public:
    std::size_t operator()(nonstd::wstring_view v) const nssv_noexcept
    {
        return std::hash<std::wstring>()(std::wstring(v.data(), v.size()));
    }
};

template<>
struct hash<nonstd::u16string_view> {
public:
    std::size_t operator()(nonstd::u16string_view v) const nssv_noexcept
    {
        return std::hash<std::u16string>()(std::u16string(v.data(), v.size()));
    }
};

template<>
struct hash<nonstd::u32string_view> {
public:
    std::size_t operator()(nonstd::u32string_view v) const nssv_noexcept
    {
        return std::hash<std::u32string>()(std::u32string(v.data(), v.size()));
    }
};

}// namespace std

#endif// nssv_HAVE_STD_HASH

nssv_RESTORE_WARNINGS()

#endif// nssv_HAVE_STD_STRING_VIEW
namespace ulib {
using string_view = nonstd::string_view;
}
#endif// NONSTD_SV_LITE_H_INCLUDED