Cate/include/nonstd/string_view.hpp

// 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 literals::string_view_literals

#endif // nssv_CONFIG_USR_SV_OPERATOR

} // namespace nonstd

#endif // nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

namespace nonstd {

using std::string_view;
using std::wstring_view;
using std::u16string_view;
using std::u32string_view;
using std::basic_string_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 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::literals::string_view_literals

#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 nonstd::sv_lite

#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
#endif // NONSTD_SV_LITE_H_INCLUDED