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      1 ///////////////////////////////////////////////////////////////////////////////
      2 //
      3 // Copyright (c) 2015 Microsoft Corporation. All rights reserved.
      4 //
      5 // This code is licensed under the MIT License (MIT).
      6 //
      7 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
      8 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
      9 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     10 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     11 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
     12 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
     13 // THE SOFTWARE.
     14 //
     15 ///////////////////////////////////////////////////////////////////////////////
     16 
     17 #pragma once
     18 
     19 #ifndef GSL_STRING_SPAN_H
     20 #define GSL_STRING_SPAN_H
     21 
     22 #include <gsl/gsl_assert>
     23 #include <gsl/gsl_util>
     24 #include <gsl/span>
     25 
     26 #include <cstdint>
     27 #include <cstring>
     28 #include <string>
     29 
     30 #ifdef _MSC_VER
     31 #pragma warning(push)
     32 
     33 // blanket turn off warnings from CppCoreCheck for now
     34 // so people aren't annoyed by them when running the tool.
     35 // more targeted suppressions will be added in a future update to the GSL
     36 #pragma warning(disable : 26481 26482 26483 26485 26490 26491 26492 26493 26495)
     37 
     38 #if _MSC_VER < 1910
     39 #pragma push_macro("constexpr")
     40 #define constexpr /*constexpr*/
     41 
     42 #endif           // _MSC_VER < 1910
     43 #endif           // _MSC_VER
     44 
     45 // In order to test the library, we need it to throw exceptions that we can catch
     46 #ifdef GSL_THROW_ON_CONTRACT_VIOLATION
     47 #define GSL_NOEXCEPT /*noexcept*/
     48 #else
     49 #define GSL_NOEXCEPT noexcept
     50 #endif // GSL_THROW_ON_CONTRACT_VIOLATION
     51 
     52 namespace gsl
     53 {
     54 //
     55 // czstring and wzstring
     56 //
     57 // These are "tag" typedefs for C-style strings (i.e. null-terminated character arrays)
     58 // that allow static analysis to help find bugs.
     59 //
     60 // There are no additional features/semantics that we can find a way to add inside the
     61 // type system for these types that will not either incur significant runtime costs or
     62 // (sometimes needlessly) break existing programs when introduced.
     63 //
     64 
     65 template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
     66 using basic_zstring = CharT*;
     67 
     68 template <std::ptrdiff_t Extent = dynamic_extent>
     69 using czstring = basic_zstring<const char, Extent>;
     70 
     71 template <std::ptrdiff_t Extent = dynamic_extent>
     72 using cwzstring = basic_zstring<const wchar_t, Extent>;
     73 
     74 template <std::ptrdiff_t Extent = dynamic_extent>
     75 using zstring = basic_zstring<char, Extent>;
     76 
     77 template <std::ptrdiff_t Extent = dynamic_extent>
     78 using wzstring = basic_zstring<wchar_t, Extent>;
     79 
     80 namespace details
     81 {
     82     inline std::ptrdiff_t string_length(const char* str, std::ptrdiff_t n)
     83     {
     84         if (str == nullptr || n <= 0) return 0;
     85 
     86         span<const char> str_span{str, n};
     87 
     88         std::ptrdiff_t len = 0;
     89         while (len < n && str_span[len]) len++;
     90 
     91         return len;
     92     }
     93 
     94     inline std::ptrdiff_t wstring_length(const wchar_t* str, std::ptrdiff_t n)
     95     {
     96         if (str == nullptr || n <= 0) return 0;
     97 
     98         span<const wchar_t> str_span{str, n};
     99 
    100         std::ptrdiff_t len = 0;
    101         while (len < n && str_span[len]) len++;
    102 
    103         return len;
    104     }
    105 }
    106 
    107 //
    108 // ensure_sentinel()
    109 //
    110 // Provides a way to obtain an span from a contiguous sequence
    111 // that ends with a (non-inclusive) sentinel value.
    112 //
    113 // Will fail-fast if sentinel cannot be found before max elements are examined.
    114 //
    115 template <typename T, const T Sentinel>
    116 span<T, dynamic_extent> ensure_sentinel(T* seq, std::ptrdiff_t max = PTRDIFF_MAX)
    117 {
    118     auto cur = seq;
    119     while ((cur - seq) < max && *cur != Sentinel) ++cur;
    120     Ensures(*cur == Sentinel);
    121     return {seq, cur - seq};
    122 }
    123 
    124 //
    125 // ensure_z - creates a span for a czstring or cwzstring.
    126 // Will fail fast if a null-terminator cannot be found before
    127 // the limit of size_type.
    128 //
    129 template <typename T>
    130 inline span<T, dynamic_extent> ensure_z(T* const& sz, std::ptrdiff_t max = PTRDIFF_MAX)
    131 {
    132     return ensure_sentinel<T, 0>(sz, max);
    133 }
    134 
    135 // TODO (neilmac) there is probably a better template-magic way to get the const and non-const
    136 // overloads to share an implementation
    137 inline span<char, dynamic_extent> ensure_z(char* const& sz, std::ptrdiff_t max)
    138 {
    139     auto len = details::string_length(sz, max);
    140     Ensures(sz[len] == 0);
    141     return {sz, len};
    142 }
    143 
    144 inline span<const char, dynamic_extent> ensure_z(const char* const& sz, std::ptrdiff_t max)
    145 {
    146     auto len = details::string_length(sz, max);
    147     Ensures(sz[len] == 0);
    148     return {sz, len};
    149 }
    150 
    151 inline span<wchar_t, dynamic_extent> ensure_z(wchar_t* const& sz, std::ptrdiff_t max)
    152 {
    153     auto len = details::wstring_length(sz, max);
    154     Ensures(sz[len] == 0);
    155     return {sz, len};
    156 }
    157 
    158 inline span<const wchar_t, dynamic_extent> ensure_z(const wchar_t* const& sz, std::ptrdiff_t max)
    159 {
    160     auto len = details::wstring_length(sz, max);
    161     Ensures(sz[len] == 0);
    162     return {sz, len};
    163 }
    164 
    165 template <typename T, std::size_t N>
    166 span<T, dynamic_extent> ensure_z(T (&sz)[N])
    167 {
    168     return ensure_z(&sz[0], static_cast<std::ptrdiff_t>(N));
    169 }
    170 
    171 template <class Cont>
    172 span<typename std::remove_pointer<typename Cont::pointer>::type, dynamic_extent>
    173 ensure_z(Cont& cont)
    174 {
    175     return ensure_z(cont.data(), static_cast<std::ptrdiff_t>(cont.length()));
    176 }
    177 
    178 template <typename CharT, std::ptrdiff_t>
    179 class basic_string_span;
    180 
    181 namespace details
    182 {
    183     template <typename T>
    184     struct is_basic_string_span_oracle : std::false_type
    185     {
    186     };
    187 
    188     template <typename CharT, std::ptrdiff_t Extent>
    189     struct is_basic_string_span_oracle<basic_string_span<CharT, Extent>> : std::true_type
    190     {
    191     };
    192 
    193     template <typename T>
    194     struct is_basic_string_span : is_basic_string_span_oracle<std::remove_cv_t<T>>
    195     {
    196     };
    197 
    198     template <typename T>
    199     struct length_func
    200     {
    201     };
    202 
    203     template <>
    204     struct length_func<char>
    205     {
    206         std::ptrdiff_t operator()(const char* const ptr, std::ptrdiff_t length) GSL_NOEXCEPT
    207         {
    208             return details::string_length(ptr, length);
    209         }
    210     };
    211 
    212     template <>
    213     struct length_func<wchar_t>
    214     {
    215         std::ptrdiff_t operator()(const wchar_t* const ptr, std::ptrdiff_t length) GSL_NOEXCEPT
    216         {
    217             return details::wstring_length(ptr, length);
    218         }
    219     };
    220 
    221     template <>
    222     struct length_func<const char>
    223     {
    224         std::ptrdiff_t operator()(const char* const ptr, std::ptrdiff_t length) GSL_NOEXCEPT
    225         {
    226             return details::string_length(ptr, length);
    227         }
    228     };
    229 
    230     template <>
    231     struct length_func<const wchar_t>
    232     {
    233         std::ptrdiff_t operator()(const wchar_t* const ptr, std::ptrdiff_t length) GSL_NOEXCEPT
    234         {
    235             return details::wstring_length(ptr, length);
    236         }
    237     };
    238 }
    239 
    240 //
    241 // string_span and relatives
    242 //
    243 template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
    244 class basic_string_span
    245 {
    246 public:
    247     using element_type = CharT;
    248     using pointer = std::add_pointer_t<element_type>;
    249     using reference = std::add_lvalue_reference_t<element_type>;
    250     using const_reference = std::add_lvalue_reference_t<std::add_const_t<element_type>>;
    251     using impl_type = span<element_type, Extent>;
    252 
    253     using index_type = typename impl_type::index_type;
    254     using iterator = typename impl_type::iterator;
    255     using const_iterator = typename impl_type::const_iterator;
    256     using reverse_iterator = typename impl_type::reverse_iterator;
    257     using const_reverse_iterator = typename impl_type::const_reverse_iterator;
    258 
    259     // default (empty)
    260     constexpr basic_string_span() GSL_NOEXCEPT = default;
    261 
    262     // copy
    263     constexpr basic_string_span(const basic_string_span& other) GSL_NOEXCEPT = default;
    264 
    265 // move
    266     constexpr basic_string_span(basic_string_span&& other) GSL_NOEXCEPT = default;
    267 
    268     // assign
    269     constexpr basic_string_span& operator=(const basic_string_span& other) GSL_NOEXCEPT = default;
    270 
    271 // move assign
    272     constexpr basic_string_span& operator=(basic_string_span&& other) GSL_NOEXCEPT = default;
    273 
    274     // from nullptr
    275     constexpr basic_string_span(std::nullptr_t ptr) GSL_NOEXCEPT : span_(ptr) {}
    276 
    277     constexpr basic_string_span(pointer ptr, index_type length) : span_(ptr, length) {}
    278     constexpr basic_string_span(pointer firstElem, pointer lastElem) : span_(firstElem, lastElem) {}
    279 
    280     // From static arrays - if 0-terminated, remove 0 from the view
    281     // All other containers allow 0s within the length, so we do not remove them
    282     template <std::size_t N>
    283     constexpr basic_string_span(element_type (&arr)[N]) : span_(remove_z(arr))
    284     {
    285     }
    286 
    287     template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
    288     constexpr basic_string_span(std::array<ArrayElementType, N>& arr) GSL_NOEXCEPT : span_(arr)
    289     {
    290     }
    291 
    292     template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
    293     constexpr basic_string_span(const std::array<ArrayElementType, N>& arr) GSL_NOEXCEPT
    294         : span_(arr)
    295     {
    296     }
    297 
    298     // Container signature should work for basic_string after C++17 version exists
    299     template <class Traits, class Allocator>
    300     constexpr basic_string_span(std::basic_string<element_type, Traits, Allocator>& str)
    301         : span_(&str[0], narrow_cast<std::ptrdiff_t>(str.length()))
    302     {
    303     }
    304 
    305     template <class Traits, class Allocator>
    306     constexpr basic_string_span(const std::basic_string<element_type, Traits, Allocator>& str)
    307         : span_(&str[0], str.length())
    308     {
    309     }
    310 
    311     // from containers. Containers must have a pointer type and data() function signatures
    312     template <class Container,
    313               class = std::enable_if_t<
    314                   !details::is_basic_string_span<Container>::value &&
    315                   std::is_convertible<typename Container::pointer, pointer>::value &&
    316                   std::is_convertible<typename Container::pointer,
    317                                       decltype(std::declval<Container>().data())>::value>>
    318     constexpr basic_string_span(Container& cont) : span_(cont)
    319     {
    320     }
    321 
    322     template <class Container,
    323               class = std::enable_if_t<
    324                   !details::is_basic_string_span<Container>::value &&
    325                   std::is_convertible<typename Container::pointer, pointer>::value &&
    326                   std::is_convertible<typename Container::pointer,
    327                                       decltype(std::declval<Container>().data())>::value>>
    328     constexpr basic_string_span(const Container& cont) : span_(cont)
    329     {
    330     }
    331 
    332     // from string_span
    333     template <
    334         class OtherValueType, std::ptrdiff_t OtherExtent,
    335         class = std::enable_if_t<std::is_convertible<
    336             typename basic_string_span<OtherValueType, OtherExtent>::impl_type, impl_type>::value>>
    337     constexpr basic_string_span(basic_string_span<OtherValueType, OtherExtent> other)
    338         : span_(other.data(), other.length())
    339     {
    340     }
    341 
    342     template <index_type Count>
    343     constexpr basic_string_span<element_type, Count> first() const
    344     {
    345         return {span_.template first<Count>()};
    346     }
    347 
    348     constexpr basic_string_span<element_type, dynamic_extent> first(index_type count) const
    349     {
    350         return {span_.first(count)};
    351     }
    352 
    353     template <index_type Count>
    354     constexpr basic_string_span<element_type, Count> last() const
    355     {
    356         return {span_.template last<Count>()};
    357     }
    358 
    359     constexpr basic_string_span<element_type, dynamic_extent> last(index_type count) const
    360     {
    361         return {span_.last(count)};
    362     }
    363 
    364     template <index_type Offset, index_type Count>
    365     constexpr basic_string_span<element_type, Count> subspan() const
    366     {
    367         return {span_.template subspan<Offset, Count>()};
    368     }
    369 
    370     constexpr basic_string_span<element_type, dynamic_extent>
    371     subspan(index_type offset, index_type count = dynamic_extent) const
    372     {
    373         return {span_.subspan(offset, count)};
    374     }
    375 
    376     constexpr reference operator[](index_type idx) const { return span_[idx]; }
    377     constexpr reference operator()(index_type idx) const { return span_[idx]; }
    378 
    379     constexpr pointer data() const { return span_.data(); }
    380 
    381     constexpr index_type length() const GSL_NOEXCEPT { return span_.size(); }
    382     constexpr index_type size() const GSL_NOEXCEPT { return span_.size(); }
    383     constexpr index_type size_bytes() const GSL_NOEXCEPT { return span_.size_bytes(); }
    384     constexpr index_type length_bytes() const GSL_NOEXCEPT { return span_.length_bytes(); }
    385     constexpr bool empty() const GSL_NOEXCEPT { return size() == 0; }
    386 
    387     constexpr iterator begin() const GSL_NOEXCEPT { return span_.begin(); }
    388     constexpr iterator end() const GSL_NOEXCEPT { return span_.end(); }
    389 
    390     constexpr const_iterator cbegin() const GSL_NOEXCEPT { return span_.cbegin(); }
    391     constexpr const_iterator cend() const GSL_NOEXCEPT { return span_.cend(); }
    392 
    393     constexpr reverse_iterator rbegin() const GSL_NOEXCEPT { return span_.rbegin(); }
    394     constexpr reverse_iterator rend() const GSL_NOEXCEPT { return span_.rend(); }
    395 
    396     constexpr const_reverse_iterator crbegin() const GSL_NOEXCEPT { return span_.crbegin(); }
    397     constexpr const_reverse_iterator crend() const GSL_NOEXCEPT { return span_.crend(); }
    398 
    399 private:
    400     static impl_type remove_z(pointer const& sz, std::ptrdiff_t max)
    401     {
    402         return {sz, details::length_func<element_type>()(sz, max)};
    403     }
    404 
    405     template <std::size_t N>
    406     static impl_type remove_z(element_type (&sz)[N])
    407     {
    408         return remove_z(&sz[0], narrow_cast<std::ptrdiff_t>(N));
    409     }
    410 
    411     impl_type span_;
    412 };
    413 
    414 template <std::ptrdiff_t Extent = dynamic_extent>
    415 using string_span = basic_string_span<char, Extent>;
    416 
    417 template <std::ptrdiff_t Extent = dynamic_extent>
    418 using cstring_span = basic_string_span<const char, Extent>;
    419 
    420 template <std::ptrdiff_t Extent = dynamic_extent>
    421 using wstring_span = basic_string_span<wchar_t, Extent>;
    422 
    423 template <std::ptrdiff_t Extent = dynamic_extent>
    424 using cwstring_span = basic_string_span<const wchar_t, Extent>;
    425 
    426 //
    427 // to_string() allow (explicit) conversions from string_span to string
    428 //
    429 
    430 template <typename CharT, std::ptrdiff_t Extent>
    431 std::basic_string<typename std::remove_const<CharT>::type>
    432 to_string(basic_string_span<CharT, Extent> view)
    433 {
    434     return {view.data(), static_cast<std::size_t>(view.length())};
    435 }
    436 
    437 template <typename CharT, typename Traits = typename std::char_traits<CharT>,
    438           typename Allocator = std::allocator<CharT>, typename gCharT, std::ptrdiff_t Extent>
    439 std::basic_string<CharT, Traits, Allocator> to_basic_string(basic_string_span<gCharT, Extent> view)
    440 {
    441     return {view.data(), static_cast<std::size_t>(view.length())};
    442 }
    443 
    444 // zero-terminated string span, used to convert
    445 // zero-terminated spans to legacy strings
    446 template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
    447 class basic_zstring_span
    448 {
    449 public:
    450     using value_type = CharT;
    451     using const_value_type = std::add_const_t<CharT>;
    452 
    453     using pointer = std::add_pointer_t<value_type>;
    454     using const_pointer = std::add_pointer_t<const_value_type>;
    455 
    456     using zstring_type = basic_zstring<value_type, Extent>;
    457     using const_zstring_type = basic_zstring<const_value_type, Extent>;
    458 
    459     using impl_type = span<value_type, Extent>;
    460     using string_span_type = basic_string_span<value_type, Extent>;
    461 
    462     constexpr basic_zstring_span(impl_type s) GSL_NOEXCEPT : span_(s)
    463     {
    464         // expects a zero-terminated span
    465         Expects(s[s.size() - 1] == '\0');
    466     }
    467 
    468     // copy
    469     constexpr basic_zstring_span(const basic_zstring_span& other) = default;
    470 
    471 // move
    472     constexpr basic_zstring_span(basic_zstring_span&& other) = default;
    473 
    474     // assign
    475     constexpr basic_zstring_span& operator=(const basic_zstring_span& other) = default;
    476 
    477 // move assign
    478     constexpr basic_zstring_span& operator=(basic_zstring_span&& other) = default;
    479 
    480     constexpr bool empty() const GSL_NOEXCEPT { return span_.size() == 0; }
    481 
    482     constexpr string_span_type as_string_span() const GSL_NOEXCEPT
    483     {
    484         auto sz = span_.size();
    485         return span_.first(sz <= 0 ? 0 : sz - 1);
    486     }
    487 
    488     constexpr string_span_type ensure_z() const GSL_NOEXCEPT { return gsl::ensure_z(span_); }
    489 
    490     constexpr const_zstring_type assume_z() const GSL_NOEXCEPT { return span_.data(); }
    491 
    492 private:
    493     impl_type span_;
    494 };
    495 
    496 template <std::ptrdiff_t Max = dynamic_extent>
    497 using zstring_span = basic_zstring_span<char, Max>;
    498 
    499 template <std::ptrdiff_t Max = dynamic_extent>
    500 using wzstring_span = basic_zstring_span<wchar_t, Max>;
    501 
    502 template <std::ptrdiff_t Max = dynamic_extent>
    503 using czstring_span = basic_zstring_span<const char, Max>;
    504 
    505 template <std::ptrdiff_t Max = dynamic_extent>
    506 using cwzstring_span = basic_zstring_span<const wchar_t, Max>;
    507 
    508 // operator ==
    509 template <class CharT, std::ptrdiff_t Extent, class T,
    510           class = std::enable_if_t<
    511               details::is_basic_string_span<T>::value ||
    512               std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>>>::value>>
    513 bool operator==(const gsl::basic_string_span<CharT, Extent>& one, const T& other) GSL_NOEXCEPT
    514 {
    515     const gsl::basic_string_span<std::add_const_t<CharT>> tmp(other);
    516     return std::equal(one.begin(), one.end(), tmp.begin(), tmp.end());
    517 }
    518 
    519 template <class CharT, std::ptrdiff_t Extent, class T,
    520           class = std::enable_if_t<
    521               !details::is_basic_string_span<T>::value &&
    522               std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>>>::value>>
    523 bool operator==(const T& one, const gsl::basic_string_span<CharT, Extent>& other) GSL_NOEXCEPT
    524 {
    525     gsl::basic_string_span<std::add_const_t<CharT>> tmp(one);
    526     return std::equal(tmp.begin(), tmp.end(), other.begin(), other.end());
    527 }
    528 
    529 // operator !=
    530 template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    531           typename = std::enable_if_t<std::is_convertible<
    532               T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
    533 bool operator!=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    534 {
    535     return !(one == other);
    536 }
    537 
    538 template <
    539     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    540     typename Dummy = std::enable_if_t<
    541         std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
    542         !gsl::details::is_basic_string_span<T>::value>>
    543 bool operator!=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    544 {
    545     return !(one == other);
    546 }
    547 
    548 // operator<
    549 template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    550           typename = std::enable_if_t<std::is_convertible<
    551               T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
    552 bool operator<(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    553 {
    554     const gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
    555     return std::lexicographical_compare(one.begin(), one.end(), tmp.begin(), tmp.end());
    556 }
    557 
    558 template <
    559     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    560     typename Dummy = std::enable_if_t<
    561         std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
    562         !gsl::details::is_basic_string_span<T>::value>>
    563 bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    564 {
    565     gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
    566     return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
    567 }
    568 
    569 #ifndef _MSC_VER
    570 
    571 // VS treats temp and const containers as convertible to basic_string_span,
    572 // so the cases below are already covered by the previous operators
    573 
    574 template <
    575     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    576     typename DataType = typename T::value_type,
    577     typename Dummy = std::enable_if_t<
    578         !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
    579         std::is_convertible<DataType*, CharT*>::value &&
    580         std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
    581                      DataType>::value>>
    582 bool operator<(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    583 {
    584     gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
    585     return std::lexicographical_compare(one.begin(), one.end(), tmp.begin(), tmp.end());
    586 }
    587 
    588 template <
    589     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    590     typename DataType = typename T::value_type,
    591     typename Dummy = std::enable_if_t<
    592         !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
    593         std::is_convertible<DataType*, CharT*>::value &&
    594         std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
    595                      DataType>::value>>
    596 bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    597 {
    598     gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
    599     return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
    600 }
    601 #endif
    602 
    603 // operator <=
    604 template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    605           typename = std::enable_if_t<std::is_convertible<
    606               T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
    607 bool operator<=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    608 {
    609     return !(other < one);
    610 }
    611 
    612 template <
    613     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    614     typename Dummy = std::enable_if_t<
    615         std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
    616         !gsl::details::is_basic_string_span<T>::value>>
    617 bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    618 {
    619     return !(other < one);
    620 }
    621 
    622 #ifndef _MSC_VER
    623 
    624 // VS treats temp and const containers as convertible to basic_string_span,
    625 // so the cases below are already covered by the previous operators
    626 
    627 template <
    628     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    629     typename DataType = typename T::value_type,
    630     typename Dummy = std::enable_if_t<
    631         !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
    632         std::is_convertible<DataType*, CharT*>::value &&
    633         std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
    634                      DataType>::value>>
    635 bool operator<=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    636 {
    637     return !(other < one);
    638 }
    639 
    640 template <
    641     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    642     typename DataType = typename T::value_type,
    643     typename Dummy = std::enable_if_t<
    644         !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
    645         std::is_convertible<DataType*, CharT*>::value &&
    646         std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
    647                      DataType>::value>>
    648 bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    649 {
    650     return !(other < one);
    651 }
    652 #endif
    653 
    654 // operator>
    655 template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    656           typename = std::enable_if_t<std::is_convertible<
    657               T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
    658 bool operator>(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    659 {
    660     return other < one;
    661 }
    662 
    663 template <
    664     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    665     typename Dummy = std::enable_if_t<
    666         std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
    667         !gsl::details::is_basic_string_span<T>::value>>
    668 bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    669 {
    670     return other < one;
    671 }
    672 
    673 #ifndef _MSC_VER
    674 
    675 // VS treats temp and const containers as convertible to basic_string_span,
    676 // so the cases below are already covered by the previous operators
    677 
    678 template <
    679     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    680     typename DataType = typename T::value_type,
    681     typename Dummy = std::enable_if_t<
    682         !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
    683         std::is_convertible<DataType*, CharT*>::value &&
    684         std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
    685                      DataType>::value>>
    686 bool operator>(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    687 {
    688     return other < one;
    689 }
    690 
    691 template <
    692     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    693     typename DataType = typename T::value_type,
    694     typename Dummy = std::enable_if_t<
    695         !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
    696         std::is_convertible<DataType*, CharT*>::value &&
    697         std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
    698                      DataType>::value>>
    699 bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    700 {
    701     return other < one;
    702 }
    703 #endif
    704 
    705 // operator >=
    706 template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    707           typename = std::enable_if_t<std::is_convertible<
    708               T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
    709 bool operator>=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    710 {
    711     return !(one < other);
    712 }
    713 
    714 template <
    715     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    716     typename Dummy = std::enable_if_t<
    717         std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
    718         !gsl::details::is_basic_string_span<T>::value>>
    719 bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    720 {
    721     return !(one < other);
    722 }
    723 
    724 #ifndef _MSC_VER
    725 
    726 // VS treats temp and const containers as convertible to basic_string_span,
    727 // so the cases below are already covered by the previous operators
    728 
    729 template <
    730     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    731     typename DataType = typename T::value_type,
    732     typename Dummy = std::enable_if_t<
    733         !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
    734         std::is_convertible<DataType*, CharT*>::value &&
    735         std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
    736                      DataType>::value>>
    737 bool operator>=(gsl::basic_string_span<CharT, Extent> one, const T& other) GSL_NOEXCEPT
    738 {
    739     return !(one < other);
    740 }
    741 
    742 template <
    743     typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
    744     typename DataType = typename T::value_type,
    745     typename Dummy = std::enable_if_t<
    746         !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
    747         std::is_convertible<DataType*, CharT*>::value &&
    748         std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
    749                      DataType>::value>>
    750 bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other) GSL_NOEXCEPT
    751 {
    752     return !(one < other);
    753 }
    754 #endif
    755 } // namespace GSL
    756 
    757 #undef GSL_NOEXCEPT
    758 
    759 #ifdef _MSC_VER
    760 #pragma warning(pop)
    761 
    762 #if _MSC_VER < 1910
    763 #undef constexpr
    764 #pragma pop_macro("constexpr")
    765 
    766 #endif // _MSC_VER < 1910
    767 #endif // _MSC_VER
    768 
    769 #endif // GSL_STRING_SPAN_H
    770