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0001 ///////////////////////////////////////////////////////////////////////////////
0002 //
0003 // Copyright (c) 2015 Microsoft Corporation. All rights reserved.
0004 //
0005 // This code is licensed under the MIT License (MIT).
0006 //
0007 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
0008 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
0009 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
0010 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
0011 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
0012 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
0013 // THE SOFTWARE.
0014 //
0015 ///////////////////////////////////////////////////////////////////////////////
0016
0017 #ifndef GSL_SPAN_H
0018 #define GSL_SPAN_H
0019
0020 #include <gsl/assert> // for Expects
0021 #include <gsl/byte> // for byte
0022 #include <gsl/util> // for narrow_cast
0023
0024 #include <array> // for array
0025 #include <cstddef> // for ptrdiff_t, size_t, nullptr_t
0026 #include <gsl/span_ext> // for span specialization of gsl::at and other span-related extensions
0027 #include <iterator> // for reverse_iterator, distance, random_access_...
0028 #include <type_traits> // for enable_if_t, declval, is_convertible, inte...
0029
0030 #if defined(_MSC_VER) && !defined(__clang__)
0031 #pragma warning(push)
0032
0033 // turn off some warnings that are noisy about our Expects statements
0034 #pragma warning(disable : 4127) // conditional expression is constant
0035 #pragma warning( \
0036 disable : 4146) // unary minus operator applied to unsigned type, result still unsigned
0037 #pragma warning(disable : 4702) // unreachable code
0038
0039 // Turn MSVC /analyze rules that generate too much noise. TODO: fix in the tool.
0040 #pragma warning(disable : 26495) // uninitalized member when constructor calls constructor
0041 #pragma warning(disable : 26446) // parser bug does not allow attributes on some templates
0042
0043 #endif // _MSC_VER
0044
0045 // See if we have enough C++17 power to use a static constexpr data member
0046 // without needing an out-of-line definition
0047 #if !(defined(__cplusplus) && (__cplusplus >= 201703L))
0048 #define GSL_USE_STATIC_CONSTEXPR_WORKAROUND
0049 #endif // !(defined(__cplusplus) && (__cplusplus >= 201703L))
0050
0051 // GCC 7 does not like the signed unsigned missmatch (size_t ptrdiff_t)
0052 // While there is a conversion from signed to unsigned, it happens at
0053 // compiletime, so the compiler wouldn't have to warn indiscriminately, but
0054 // could check if the source value actually doesn't fit into the target type
0055 // and only warn in those cases.
0056 #if defined(__GNUC__) && __GNUC__ > 6
0057 #pragma GCC diagnostic push
0058 #pragma GCC diagnostic ignored "-Wsign-conversion"
0059 #endif
0060
0061 namespace gsl
0062 {
0063
0064 // implementation details
0065 namespace details
0066 {
0067 template <class T>
0068 struct is_span_oracle : std::false_type
0069 {
0070 };
0071
0072 template <class ElementType, std::size_t Extent>
0073 struct is_span_oracle<gsl::span<ElementType, Extent>> : std::true_type
0074 {
0075 };
0076
0077 template <class T>
0078 struct is_span : public is_span_oracle<std::remove_cv_t<T>>
0079 {
0080 };
0081
0082 template <class T>
0083 struct is_std_array_oracle : std::false_type
0084 {
0085 };
0086
0087 template <class ElementType, std::size_t Extent>
0088 struct is_std_array_oracle<std::array<ElementType, Extent>> : std::true_type
0089 {
0090 };
0091
0092 template <class T>
0093 struct is_std_array : is_std_array_oracle<std::remove_cv_t<T>>
0094 {
0095 };
0096
0097 template <std::size_t From, std::size_t To>
0098 struct is_allowed_extent_conversion
0099 : std::integral_constant<bool, From == To || To == dynamic_extent>
0100 {
0101 };
0102
0103 template <class From, class To>
0104 struct is_allowed_element_type_conversion
0105 : std::integral_constant<bool, std::is_convertible<From (*)[], To (*)[]>::value>
0106 {
0107 };
0108
0109 template <class Type>
0110 class span_iterator
0111 {
0112 public:
0113 using iterator_category = std::random_access_iterator_tag;
0114 using value_type = std::remove_cv_t<Type>;
0115 using difference_type = std::ptrdiff_t;
0116 using pointer = Type*;
0117 using reference = Type&;
0118
0119 #ifdef _MSC_VER
0120 using _Unchecked_type = pointer;
0121 #endif // _MSC_VER
0122 constexpr span_iterator() = default;
0123
0124 constexpr span_iterator(pointer begin, pointer end, pointer current)
0125 : begin_(begin), end_(end), current_(current)
0126 {}
0127
0128 constexpr operator span_iterator<const Type>() const noexcept
0129 {
0130 return {begin_, end_, current_};
0131 }
0132
0133 constexpr reference operator*() const noexcept
0134 {
0135 Expects(begin_ && end_);
0136 Expects(begin_ <= current_ && current_ < end_);
0137 return *current_;
0138 }
0139
0140 constexpr pointer operator->() const noexcept
0141 {
0142 Expects(begin_ && end_);
0143 Expects(begin_ <= current_ && current_ < end_);
0144 return current_;
0145 }
0146 constexpr span_iterator& operator++() noexcept
0147 {
0148 Expects(begin_ && current_ && end_);
0149 Expects(current_ < end_);
0150 // clang-format off
0151 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0152 // clang-format on
0153 ++current_;
0154 return *this;
0155 }
0156
0157 constexpr span_iterator operator++(int) noexcept
0158 {
0159 span_iterator ret = *this;
0160 ++*this;
0161 return ret;
0162 }
0163
0164 constexpr span_iterator& operator--() noexcept
0165 {
0166 Expects(begin_ && end_);
0167 Expects(begin_ < current_);
0168 --current_;
0169 return *this;
0170 }
0171
0172 constexpr span_iterator operator--(int) noexcept
0173 {
0174 span_iterator ret = *this;
0175 --*this;
0176 return ret;
0177 }
0178
0179 constexpr span_iterator& operator+=(const difference_type n) noexcept
0180 {
0181 if (n != 0) Expects(begin_ && current_ && end_);
0182 if (n > 0) Expects(end_ - current_ >= n);
0183 if (n < 0) Expects(current_ - begin_ >= -n);
0184 // clang-format off
0185 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0186 // clang-format on
0187 current_ += n;
0188 return *this;
0189 }
0190
0191 constexpr span_iterator operator+(const difference_type n) const noexcept
0192 {
0193 span_iterator ret = *this;
0194 ret += n;
0195 return ret;
0196 }
0197
0198 friend constexpr span_iterator operator+(const difference_type n,
0199 const span_iterator& rhs) noexcept
0200 {
0201 return rhs + n;
0202 }
0203
0204 constexpr span_iterator& operator-=(const difference_type n) noexcept
0205 {
0206 if (n != 0) Expects(begin_ && current_ && end_);
0207 if (n > 0) Expects(current_ - begin_ >= n);
0208 if (n < 0) Expects(end_ - current_ >= -n);
0209 current_ -= n;
0210 return *this;
0211 }
0212
0213 constexpr span_iterator operator-(const difference_type n) const noexcept
0214 {
0215 span_iterator ret = *this;
0216 ret -= n;
0217 return ret;
0218 }
0219
0220 template <
0221 class Type2,
0222 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
0223 constexpr difference_type operator-(const span_iterator<Type2>& rhs) const noexcept
0224 {
0225 Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
0226 return current_ - rhs.current_;
0227 }
0228
0229 constexpr reference operator[](const difference_type n) const noexcept
0230 {
0231 return *(*this + n);
0232 }
0233
0234 template <
0235 class Type2,
0236 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
0237 constexpr bool operator==(const span_iterator<Type2>& rhs) const noexcept
0238 {
0239 Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
0240 return current_ == rhs.current_;
0241 }
0242
0243 template <
0244 class Type2,
0245 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
0246 constexpr bool operator!=(const span_iterator<Type2>& rhs) const noexcept
0247 {
0248 return !(*this == rhs);
0249 }
0250
0251 template <
0252 class Type2,
0253 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
0254 constexpr bool operator<(const span_iterator<Type2>& rhs) const noexcept
0255 {
0256 Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
0257 return current_ < rhs.current_;
0258 }
0259
0260 template <
0261 class Type2,
0262 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
0263 constexpr bool operator>(const span_iterator<Type2>& rhs) const noexcept
0264 {
0265 return rhs < *this;
0266 }
0267
0268 template <
0269 class Type2,
0270 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
0271 constexpr bool operator<=(const span_iterator<Type2>& rhs) const noexcept
0272 {
0273 return !(rhs < *this);
0274 }
0275
0276 template <
0277 class Type2,
0278 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
0279 constexpr bool operator>=(const span_iterator<Type2>& rhs) const noexcept
0280 {
0281 return !(*this < rhs);
0282 }
0283
0284 #ifdef _MSC_VER
0285 // MSVC++ iterator debugging support; allows STL algorithms in 15.8+
0286 // to unwrap span_iterator to a pointer type after a range check in STL
0287 // algorithm calls
0288 friend constexpr void _Verify_range(span_iterator lhs, span_iterator rhs) noexcept
0289 { // test that [lhs, rhs) forms a valid range inside an STL algorithm
0290 Expects(lhs.begin_ == rhs.begin_ // range spans have to match
0291 && lhs.end_ == rhs.end_ &&
0292 lhs.current_ <= rhs.current_); // range must not be transposed
0293 }
0294
0295 constexpr void _Verify_offset(const difference_type n) const noexcept
0296 { // test that *this + n is within the range of this call
0297 if (n != 0) Expects(begin_ && current_ && end_);
0298 if (n > 0) Expects(end_ - current_ >= n);
0299 if (n < 0) Expects(current_ - begin_ >= -n);
0300 }
0301
0302 // clang-format off
0303 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0304 // clang-format on
0305 constexpr pointer _Unwrapped() const noexcept
0306 { // after seeking *this to a high water mark, or using one of the
0307 // _Verify_xxx functions above, unwrap this span_iterator to a raw
0308 // pointer
0309 return current_;
0310 }
0311
0312 // Tell the STL that span_iterator should not be unwrapped if it can't
0313 // validate in advance, even in release / optimized builds:
0314 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
0315 static constexpr const bool _Unwrap_when_unverified = false;
0316 #else
0317 static constexpr bool _Unwrap_when_unverified = false;
0318 #endif
0319 // clang-format off
0320 GSL_SUPPRESS(con.3) // NO-FORMAT: attribute // TODO: false positive
0321 // clang-format on
0322 constexpr void _Seek_to(const pointer p) noexcept
0323 { // adjust the position of *this to previously verified location p
0324 // after _Unwrapped
0325 current_ = p;
0326 }
0327 #endif
0328
0329 pointer begin_ = nullptr;
0330 pointer end_ = nullptr;
0331 pointer current_ = nullptr;
0332 };
0333
0334 template <std::size_t Ext>
0335 class extent_type
0336 {
0337 public:
0338 using size_type = std::size_t;
0339
0340 constexpr extent_type() noexcept = default;
0341
0342 constexpr explicit extent_type(extent_type<dynamic_extent>);
0343
0344 constexpr explicit extent_type(size_type size) { Expects(size == Ext); }
0345
0346 constexpr size_type size() const noexcept { return Ext; }
0347
0348 private:
0349 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
0350 static constexpr const size_type size_ = Ext; // static size equal to Ext
0351 #else
0352 static constexpr size_type size_ = Ext; // static size equal to Ext
0353 #endif
0354 };
0355
0356 template <>
0357 class extent_type<dynamic_extent>
0358 {
0359 public:
0360 using size_type = std::size_t;
0361
0362 template <size_type Other>
0363 constexpr explicit extent_type(extent_type<Other> ext) : size_(ext.size())
0364 {}
0365
0366 constexpr explicit extent_type(size_type size) : size_(size)
0367 {
0368 Expects(size != dynamic_extent);
0369 }
0370
0371 constexpr size_type size() const noexcept { return size_; }
0372
0373 private:
0374 size_type size_;
0375 };
0376
0377 template <std::size_t Ext>
0378 constexpr extent_type<Ext>::extent_type(extent_type<dynamic_extent> ext)
0379 {
0380 Expects(ext.size() == Ext);
0381 }
0382
0383 template <class ElementType, std::size_t Extent, std::size_t Offset, std::size_t Count>
0384 struct calculate_subspan_type
0385 {
0386 using type = span<ElementType, Count != dynamic_extent
0387 ? Count
0388 : (Extent != dynamic_extent ? Extent - Offset : Extent)>;
0389 };
0390 } // namespace details
0391
0392 // [span], class template span
0393 template <class ElementType, std::size_t Extent>
0394 class span
0395 {
0396 public:
0397 // constants and types
0398 using element_type = ElementType;
0399 using value_type = std::remove_cv_t<ElementType>;
0400 using size_type = std::size_t;
0401 using pointer = element_type*;
0402 using const_pointer = const element_type*;
0403 using reference = element_type&;
0404 using const_reference = const element_type&;
0405 using difference_type = std::ptrdiff_t;
0406
0407 using iterator = details::span_iterator<ElementType>;
0408 using reverse_iterator = std::reverse_iterator<iterator>;
0409
0410 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
0411 static constexpr const size_type extent{Extent};
0412 #else
0413 static constexpr size_type extent{Extent};
0414 #endif
0415
0416 // [span.cons], span constructors, copy, assignment, and destructor
0417 template <bool Dependent = false,
0418 // "Dependent" is needed to make "std::enable_if_t<Dependent || Extent == 0 || Extent
0419 // == dynamic_extent>" SFINAE, since "std::enable_if_t<Extent == 0 || Extent ==
0420 // dynamic_extent>" is ill-formed when Extent is greater than 0.
0421 class = std::enable_if_t<(Dependent ||
0422 details::is_allowed_extent_conversion<0, Extent>::value)>>
0423 constexpr span() noexcept : storage_(nullptr, details::extent_type<0>())
0424 {}
0425
0426 template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent != dynamic_extent, int> = 0>
0427 constexpr explicit span(pointer ptr, size_type count) noexcept : storage_(ptr, count)
0428 {
0429 Expects(count == Extent);
0430 }
0431
0432 template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent == dynamic_extent, int> = 0>
0433 constexpr span(pointer ptr, size_type count) noexcept : storage_(ptr, count)
0434 {}
0435
0436 template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent != dynamic_extent, int> = 0>
0437 constexpr explicit span(pointer firstElem, pointer lastElem) noexcept
0438 : storage_(firstElem, narrow_cast<std::size_t>(lastElem - firstElem))
0439 {
0440 Expects(lastElem - firstElem == static_cast<difference_type>(Extent));
0441 }
0442
0443 template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent == dynamic_extent, int> = 0>
0444 constexpr span(pointer firstElem, pointer lastElem) noexcept
0445 : storage_(firstElem, narrow_cast<std::size_t>(lastElem - firstElem))
0446 {}
0447
0448 template <std::size_t N,
0449 std::enable_if_t<details::is_allowed_extent_conversion<N, Extent>::value, int> = 0>
0450 constexpr span(element_type (&arr)[N]) noexcept
0451 : storage_(KnownNotNull{arr}, details::extent_type<N>())
0452 {}
0453
0454 template <
0455 class T, std::size_t N,
0456 std::enable_if_t<(details::is_allowed_extent_conversion<N, Extent>::value &&
0457 details::is_allowed_element_type_conversion<T, element_type>::value),
0458 int> = 0>
0459 constexpr span(std::array<T, N>& arr) noexcept
0460 : storage_(KnownNotNull{arr.data()}, details::extent_type<N>())
0461 {}
0462
0463 template <class T, std::size_t N,
0464 std::enable_if_t<
0465 (details::is_allowed_extent_conversion<N, Extent>::value &&
0466 details::is_allowed_element_type_conversion<const T, element_type>::value),
0467 int> = 0>
0468 constexpr span(const std::array<T, N>& arr) noexcept
0469 : storage_(KnownNotNull{arr.data()}, details::extent_type<N>())
0470 {}
0471
0472 // NB: the SFINAE on these constructors uses .data() as an incomplete/imperfect proxy for the
0473 // requirement on Container to be a contiguous sequence container.
0474 template <std::size_t MyExtent = Extent, class Container,
0475 std::enable_if_t<
0476 MyExtent != dynamic_extent && !details::is_span<Container>::value &&
0477 !details::is_std_array<Container>::value &&
0478 std::is_pointer<decltype(std::declval<Container&>().data())>::value &&
0479 std::is_convertible<
0480 std::remove_pointer_t<decltype(std::declval<Container&>().data())> (*)[],
0481 element_type (*)[]>::value,
0482 int> = 0>
0483 constexpr explicit span(Container& cont) noexcept : span(cont.data(), cont.size())
0484 {}
0485
0486 template <std::size_t MyExtent = Extent, class Container,
0487 std::enable_if_t<
0488 MyExtent == dynamic_extent && !details::is_span<Container>::value &&
0489 !details::is_std_array<Container>::value &&
0490 std::is_pointer<decltype(std::declval<Container&>().data())>::value &&
0491 std::is_convertible<
0492 std::remove_pointer_t<decltype(std::declval<Container&>().data())> (*)[],
0493 element_type (*)[]>::value,
0494 int> = 0>
0495 constexpr span(Container& cont) noexcept : span(cont.data(), cont.size())
0496 {}
0497
0498 template <
0499 std::size_t MyExtent = Extent, class Container,
0500 std::enable_if_t<
0501 MyExtent != dynamic_extent && std::is_const<element_type>::value &&
0502 !details::is_span<Container>::value && !details::is_std_array<Container>::value &&
0503 std::is_pointer<decltype(std::declval<const Container&>().data())>::value &&
0504 std::is_convertible<
0505 std::remove_pointer_t<decltype(std::declval<const Container&>().data())> (*)[],
0506 element_type (*)[]>::value,
0507 int> = 0>
0508 constexpr explicit span(const Container& cont) noexcept : span(cont.data(), cont.size())
0509 {}
0510
0511 template <
0512 std::size_t MyExtent = Extent, class Container,
0513 std::enable_if_t<
0514 MyExtent == dynamic_extent && std::is_const<element_type>::value &&
0515 !details::is_span<Container>::value && !details::is_std_array<Container>::value &&
0516 std::is_pointer<decltype(std::declval<const Container&>().data())>::value &&
0517 std::is_convertible<
0518 std::remove_pointer_t<decltype(std::declval<const Container&>().data())> (*)[],
0519 element_type (*)[]>::value,
0520 int> = 0>
0521 constexpr span(const Container& cont) noexcept : span(cont.data(), cont.size())
0522 {}
0523
0524 constexpr span(const span& other) noexcept = default;
0525
0526 template <class OtherElementType, std::size_t OtherExtent, std::size_t MyExtent = Extent,
0527 std::enable_if_t<(MyExtent == dynamic_extent || MyExtent == OtherExtent) &&
0528 details::is_allowed_element_type_conversion<OtherElementType,
0529 element_type>::value,
0530 int> = 0>
0531 constexpr span(const span<OtherElementType, OtherExtent>& other) noexcept
0532 : storage_(other.data(), details::extent_type<OtherExtent>(other.size()))
0533 {}
0534
0535 template <class OtherElementType, std::size_t OtherExtent, std::size_t MyExtent = Extent,
0536 std::enable_if_t<MyExtent != dynamic_extent && OtherExtent == dynamic_extent &&
0537 details::is_allowed_element_type_conversion<OtherElementType,
0538 element_type>::value,
0539 int> = 0>
0540 constexpr explicit span(const span<OtherElementType, OtherExtent>& other) noexcept
0541 : storage_(other.data(), details::extent_type<OtherExtent>(other.size()))
0542 {}
0543
0544 ~span() noexcept = default;
0545 constexpr span& operator=(const span& other) noexcept = default;
0546
0547 // [span.sub], span subviews
0548 template <std::size_t Count>
0549 constexpr span<element_type, Count> first() const noexcept
0550 {
0551 Expects(Count <= size());
0552 return span<element_type, Count>{data(), Count};
0553 }
0554
0555 template <std::size_t Count>
0556 // clang-format off
0557 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0558 // clang-format on
0559 constexpr span<element_type, Count> last() const noexcept
0560 {
0561 Expects(Count <= size());
0562 return span<element_type, Count>{data() + (size() - Count), Count};
0563 }
0564
0565 template <std::size_t Offset, std::size_t Count = dynamic_extent>
0566 // clang-format off
0567 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0568 // clang-format on
0569 constexpr auto subspan() const noexcept ->
0570 typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type
0571 {
0572 Expects((size() >= Offset) && (Count == dynamic_extent || (Count <= size() - Offset)));
0573 using type =
0574 typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type;
0575 return type{data() + Offset, Count == dynamic_extent ? size() - Offset : Count};
0576 }
0577
0578 constexpr span<element_type, dynamic_extent> first(size_type count) const noexcept
0579 {
0580 Expects(count <= size());
0581 return {data(), count};
0582 }
0583
0584 constexpr span<element_type, dynamic_extent> last(size_type count) const noexcept
0585 {
0586 Expects(count <= size());
0587 return make_subspan(size() - count, dynamic_extent, subspan_selector<Extent>{});
0588 }
0589
0590 constexpr span<element_type, dynamic_extent>
0591 subspan(size_type offset, size_type count = dynamic_extent) const noexcept
0592 {
0593 return make_subspan(offset, count, subspan_selector<Extent>{});
0594 }
0595
0596 // [span.obs], span observers
0597 constexpr size_type size() const noexcept { return storage_.size(); }
0598
0599 constexpr size_type size_bytes() const noexcept
0600 {
0601 Expects(size() < dynamic_extent / sizeof(element_type));
0602 return size() * sizeof(element_type);
0603 }
0604
0605 constexpr bool empty() const noexcept { return size() == 0; }
0606
0607 // [span.elem], span element access
0608 // clang-format off
0609 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0610 // clang-format on
0611 constexpr reference operator[](size_type idx) const noexcept
0612 {
0613 Expects(idx < size());
0614 return data()[idx];
0615 }
0616
0617 constexpr reference front() const noexcept
0618 {
0619 Expects(size() > 0);
0620 return data()[0];
0621 }
0622
0623 constexpr reference back() const noexcept
0624 {
0625 Expects(size() > 0);
0626 return data()[size() - 1];
0627 }
0628
0629 constexpr pointer data() const noexcept { return storage_.data(); }
0630
0631 // [span.iter], span iterator support
0632 constexpr iterator begin() const noexcept
0633 {
0634 const auto data = storage_.data();
0635 // clang-format off
0636 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0637 // clang-format on
0638 return {data, data + size(), data};
0639 }
0640
0641 constexpr iterator end() const noexcept
0642 {
0643 const auto data = storage_.data();
0644 // clang-format off
0645 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0646 // clang-format on
0647 const auto endData = data + storage_.size();
0648 return {data, endData, endData};
0649 }
0650
0651 constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
0652 constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
0653
0654 #ifdef _MSC_VER
0655 // Tell MSVC how to unwrap spans in range-based-for
0656 constexpr pointer _Unchecked_begin() const noexcept { return data(); }
0657 constexpr pointer _Unchecked_end() const noexcept
0658 {
0659 // clang-format off
0660 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0661 // clang-format on
0662 return data() + size();
0663 }
0664 #endif // _MSC_VER
0665
0666 private:
0667 // Needed to remove unnecessary null check in subspans
0668 struct KnownNotNull
0669 {
0670 pointer p;
0671 };
0672
0673 // this implementation detail class lets us take advantage of the
0674 // empty base class optimization to pay for only storage of a single
0675 // pointer in the case of fixed-size spans
0676 template <class ExtentType>
0677 class storage_type : public ExtentType
0678 {
0679 public:
0680 // KnownNotNull parameter is needed to remove unnecessary null check
0681 // in subspans and constructors from arrays
0682 template <class OtherExtentType>
0683 constexpr storage_type(KnownNotNull data, OtherExtentType ext)
0684 : ExtentType(ext), data_(data.p)
0685 {
0686 Expects(ExtentType::size() != dynamic_extent);
0687 }
0688
0689 template <class OtherExtentType>
0690 constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data)
0691 {
0692 Expects(ExtentType::size() != dynamic_extent);
0693 Expects(data || ExtentType::size() == 0);
0694 }
0695
0696 constexpr pointer data() const noexcept { return data_; }
0697
0698 private:
0699 pointer data_;
0700 };
0701
0702 storage_type<details::extent_type<Extent>> storage_;
0703
0704 // The rest is needed to remove unnecessary null check
0705 // in subspans and constructors from arrays
0706 constexpr span(KnownNotNull ptr, size_type count) noexcept : storage_(ptr, count) {}
0707
0708 template <std::size_t CallerExtent>
0709 class subspan_selector
0710 {
0711 };
0712
0713 template <std::size_t CallerExtent>
0714 constexpr span<element_type, dynamic_extent>
0715 make_subspan(size_type offset, size_type count, subspan_selector<CallerExtent>) const noexcept
0716 {
0717 const span<element_type, dynamic_extent> tmp(*this);
0718 return tmp.subspan(offset, count);
0719 }
0720
0721 // clang-format off
0722 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
0723 // clang-format on
0724 constexpr span<element_type, dynamic_extent>
0725 make_subspan(size_type offset, size_type count, subspan_selector<dynamic_extent>) const noexcept
0726 {
0727 Expects(size() >= offset);
0728
0729 if (count == dynamic_extent) { return {KnownNotNull{data() + offset}, size() - offset}; }
0730
0731 Expects(size() - offset >= count);
0732 return {KnownNotNull{data() + offset}, count};
0733 }
0734 };
0735
0736 #if (defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L))
0737
0738 // Deduction Guides
0739 template <class Type, std::size_t Extent>
0740 span(Type (&)[Extent]) -> span<Type, Extent>;
0741
0742 template <class Type, std::size_t Size>
0743 span(std::array<Type, Size>&) -> span<Type, Size>;
0744
0745 template <class Type, std::size_t Size>
0746 span(const std::array<Type, Size>&) -> span<const Type, Size>;
0747
0748 template <class Container,
0749 class Element = std::remove_pointer_t<decltype(std::declval<Container&>().data())>>
0750 span(Container&) -> span<Element>;
0751
0752 template <class Container,
0753 class Element = std::remove_pointer_t<decltype(std::declval<const Container&>().data())>>
0754 span(const Container&) -> span<Element>;
0755
0756 #endif // ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
0757
0758 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
0759 template <class ElementType, std::size_t Extent>
0760 constexpr const typename span<ElementType, Extent>::size_type span<ElementType, Extent>::extent;
0761 #endif
0762
0763 namespace details
0764 {
0765 // if we only supported compilers with good constexpr support then
0766 // this pair of classes could collapse down to a constexpr function
0767
0768 // we should use a narrow_cast<> to go to std::size_t, but older compilers may not see it as
0769 // constexpr
0770 // and so will fail compilation of the template
0771 template <class ElementType, std::size_t Extent>
0772 struct calculate_byte_size : std::integral_constant<std::size_t, sizeof(ElementType) * Extent>
0773 {
0774 static_assert(Extent < dynamic_extent / sizeof(ElementType), "Size is too big.");
0775 };
0776
0777 template <class ElementType>
0778 struct calculate_byte_size<ElementType, dynamic_extent>
0779 : std::integral_constant<std::size_t, dynamic_extent>
0780 {
0781 };
0782 } // namespace details
0783
0784 // [span.objectrep], views of object representation
0785 template <class ElementType, std::size_t Extent>
0786 span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
0787 as_bytes(span<ElementType, Extent> s) noexcept
0788 {
0789 using type = span<const byte, details::calculate_byte_size<ElementType, Extent>::value>;
0790
0791 // clang-format off
0792 GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
0793 // clang-format on
0794 return type{reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
0795 }
0796
0797 template <class ElementType, std::size_t Extent,
0798 std::enable_if_t<!std::is_const<ElementType>::value, int> = 0>
0799 span<byte, details::calculate_byte_size<ElementType, Extent>::value>
0800 as_writable_bytes(span<ElementType, Extent> s) noexcept
0801 {
0802 using type = span<byte, details::calculate_byte_size<ElementType, Extent>::value>;
0803
0804 // clang-format off
0805 GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
0806 // clang-format on
0807 return type{reinterpret_cast<byte*>(s.data()), s.size_bytes()};
0808 }
0809
0810 } // namespace gsl
0811
0812 #if defined(_MSC_VER) && !defined(__clang__)
0813
0814 #pragma warning(pop)
0815 #endif // _MSC_VER
0816
0817 #if defined(__GNUC__) && __GNUC__ > 6
0818 #pragma GCC diagnostic pop
0819 #endif // __GNUC__ > 6
0820
0821 #endif // GSL_SPAN_H
