1 ///////////////////////////////////////////////////////////////////////////////
3 // Copyright (c) 2015 Microsoft Corporation. All rights reserved.
5 // This code is licensed under the MIT License (MIT).
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
15 ///////////////////////////////////////////////////////////////////////////////
20 #include "assert" // for Expects
21 #include "byte" // for byte
22 #include "span_ext" // for span specialization of gsl::at and other span-related extensions
23 #include "util" // for narrow_cast
25 #include <array> // for array
26 #include <cstddef> // for ptrdiff_t, size_t, nullptr_t
27 #include <iterator> // for reverse_iterator, distance, random_access_...
28 #include <memory> // for pointer_traits
29 #include <type_traits> // for enable_if_t, declval, is_convertible, inte...
31 #if defined(__has_include) && __has_include(<version>)
35 #if defined(_MSC_VER) && !defined(__clang__)
38 // turn off some warnings that are noisy about our Expects statements
39 #pragma warning(disable : 4127) // conditional expression is constant
41 disable : 4146) // unary minus operator applied to unsigned type, result still unsigned
42 #pragma warning(disable : 4702) // unreachable code
44 // Turn MSVC /analyze rules that generate too much noise. TODO: fix in the tool.
45 #pragma warning(disable : 26495) // uninitialized member when constructor calls constructor
46 #pragma warning(disable : 26446) // parser bug does not allow attributes on some templates
50 // See if we have enough C++17 power to use a static constexpr data member
51 // without needing an out-of-line definition
52 #if !(defined(__cplusplus) && (__cplusplus >= 201703L))
53 #define GSL_USE_STATIC_CONSTEXPR_WORKAROUND
54 #endif // !(defined(__cplusplus) && (__cplusplus >= 201703L))
56 // GCC 7 does not like the signed unsigned mismatch (size_t ptrdiff_t)
57 // While there is a conversion from signed to unsigned, it happens at
58 // compiletime, so the compiler wouldn't have to warn indiscriminately, but
59 // could check if the source value actually doesn't fit into the target type
60 // and only warn in those cases.
61 #if defined(__GNUC__) && __GNUC__ > 6
62 #pragma GCC diagnostic push
63 #pragma GCC diagnostic ignored "-Wsign-conversion"
66 // Turn off clang unsafe buffer warnings as all accessed are guarded by runtime checks
67 #if defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
68 #pragma clang diagnostic push
69 #pragma clang diagnostic ignored "-Wunsafe-buffer-usage"
70 #endif // defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
75 // implementation details
79 struct is_span_oracle : std::false_type
83 template <class ElementType, std::size_t Extent>
84 struct is_span_oracle<gsl::span<ElementType, Extent>> : std::true_type
89 struct is_span : public is_span_oracle<std::remove_cv_t<T>>
94 struct is_std_array_oracle : std::false_type
98 template <class ElementType, std::size_t Extent>
99 struct is_std_array_oracle<std::array<ElementType, Extent>> : std::true_type
104 struct is_std_array : is_std_array_oracle<std::remove_cv_t<T>>
108 template <std::size_t From, std::size_t To>
109 struct is_allowed_extent_conversion
110 : std::integral_constant<bool, From == To || To == dynamic_extent>
114 template <class From, class To>
115 struct is_allowed_element_type_conversion
116 : std::integral_constant<bool, std::is_convertible<From (*)[], To (*)[]>::value>
120 template <class Type>
124 #if defined(__cpp_lib_ranges) || (defined(_MSVC_STL_VERSION) && defined(__cpp_lib_concepts))
125 using iterator_concept = std::contiguous_iterator_tag;
126 #endif // __cpp_lib_ranges
127 using iterator_category = std::random_access_iterator_tag;
128 using value_type = std::remove_cv_t<Type>;
129 using difference_type = std::ptrdiff_t;
130 using pointer = Type*;
131 using reference = Type&;
134 using _Unchecked_type = pointer;
135 using _Prevent_inheriting_unwrap = span_iterator;
137 constexpr span_iterator() = default;
139 constexpr span_iterator(pointer begin, pointer end, pointer current)
140 : begin_(begin), end_(end), current_(current)
143 constexpr operator span_iterator<const Type>() const noexcept
145 return {begin_, end_, current_};
148 constexpr reference operator*() const noexcept
150 Expects(begin_ && end_);
151 Expects(begin_ <= current_ && current_ < end_);
155 constexpr pointer operator->() const noexcept
157 Expects(begin_ && end_);
158 Expects(begin_ <= current_ && current_ < end_);
161 constexpr span_iterator& operator++() noexcept
163 Expects(begin_ && current_ && end_);
164 Expects(current_ < end_);
166 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
172 constexpr span_iterator operator++(int) noexcept
174 span_iterator ret = *this;
179 constexpr span_iterator& operator--() noexcept
181 Expects(begin_ && end_);
182 Expects(begin_ < current_);
187 constexpr span_iterator operator--(int) noexcept
189 span_iterator ret = *this;
194 constexpr span_iterator& operator+=(const difference_type n) noexcept
196 if (n != 0) Expects(begin_ && current_ && end_);
197 if (n > 0) Expects(end_ - current_ >= n);
198 if (n < 0) Expects(current_ - begin_ >= -n);
200 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
206 constexpr span_iterator operator+(const difference_type n) const noexcept
208 span_iterator ret = *this;
213 friend constexpr span_iterator operator+(const difference_type n,
214 const span_iterator& rhs) noexcept
219 constexpr span_iterator& operator-=(const difference_type n) noexcept
221 if (n != 0) Expects(begin_ && current_ && end_);
222 if (n > 0) Expects(current_ - begin_ >= n);
223 if (n < 0) Expects(end_ - current_ >= -n);
224 GSL_SUPPRESS(bounds .1)
229 constexpr span_iterator operator-(const difference_type n) const noexcept
231 span_iterator ret = *this;
238 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
239 constexpr difference_type operator-(const span_iterator<Type2>& rhs) const noexcept
241 Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
242 return current_ - rhs.current_;
245 constexpr reference operator[](const difference_type n) const noexcept
252 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
253 constexpr bool operator==(const span_iterator<Type2>& rhs) const noexcept
255 Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
256 return current_ == rhs.current_;
261 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
262 constexpr bool operator!=(const span_iterator<Type2>& rhs) const noexcept
264 return !(*this == rhs);
269 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
270 constexpr bool operator<(const span_iterator<Type2>& rhs) const noexcept
272 Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
273 return current_ < rhs.current_;
278 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
279 constexpr bool operator>(const span_iterator<Type2>& rhs) const noexcept
286 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
287 constexpr bool operator<=(const span_iterator<Type2>& rhs) const noexcept
289 return !(rhs < *this);
294 std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
295 constexpr bool operator>=(const span_iterator<Type2>& rhs) const noexcept
297 return !(*this < rhs);
301 // MSVC++ iterator debugging support; allows STL algorithms in 15.8+
302 // to unwrap span_iterator to a pointer type after a range check in STL
304 friend constexpr void _Verify_range(span_iterator lhs, span_iterator rhs) noexcept
305 { // test that [lhs, rhs) forms a valid range inside an STL algorithm
306 Expects(lhs.begin_ == rhs.begin_ // range spans have to match
307 && lhs.end_ == rhs.end_ &&
308 lhs.current_ <= rhs.current_); // range must not be transposed
311 constexpr void _Verify_offset(const difference_type n) const noexcept
312 { // test that *this + n is within the range of this call
313 if (n != 0) Expects(begin_ && current_ && end_);
314 if (n > 0) Expects(end_ - current_ >= n);
315 if (n < 0) Expects(current_ - begin_ >= -n);
319 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
321 constexpr pointer _Unwrapped() const noexcept
322 { // after seeking *this to a high water mark, or using one of the
323 // _Verify_xxx functions above, unwrap this span_iterator to a raw
328 // Tell the STL that span_iterator should not be unwrapped if it can't
329 // validate in advance, even in release / optimized builds:
330 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
331 static constexpr const bool _Unwrap_when_unverified = false;
333 static constexpr bool _Unwrap_when_unverified = false;
336 GSL_SUPPRESS(con.3) // NO-FORMAT: attribute // TODO: false positive
338 constexpr void _Seek_to(const pointer p) noexcept
339 { // adjust the position of *this to previously verified location p
345 pointer begin_ = nullptr;
346 pointer end_ = nullptr;
347 pointer current_ = nullptr;
349 template <typename Ptr>
350 friend struct std::pointer_traits;
352 }} // namespace gsl::details
356 template <class Type>
357 struct pointer_traits<::gsl::details::span_iterator<Type>>
359 using pointer = ::gsl::details::span_iterator<Type>;
360 using element_type = Type;
361 using difference_type = ptrdiff_t;
363 static constexpr element_type* to_address(const pointer i) noexcept { return i.current_; }
367 namespace gsl { namespace details {
368 template <std::size_t Ext>
372 using size_type = std::size_t;
374 constexpr extent_type() noexcept = default;
376 constexpr explicit extent_type(extent_type<dynamic_extent>);
378 constexpr explicit extent_type(size_type size) { Expects(size == Ext); }
380 constexpr size_type size() const noexcept { return Ext; }
383 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
384 static constexpr const size_type size_ = Ext; // static size equal to Ext
386 static constexpr size_type size_ = Ext; // static size equal to Ext
391 class extent_type<dynamic_extent>
394 using size_type = std::size_t;
396 template <size_type Other>
397 constexpr explicit extent_type(extent_type<Other> ext) : size_(ext.size())
400 constexpr explicit extent_type(size_type size) : size_(size)
402 Expects(size != dynamic_extent);
405 constexpr size_type size() const noexcept { return size_; }
411 template <std::size_t Ext>
412 constexpr extent_type<Ext>::extent_type(extent_type<dynamic_extent> ext)
414 Expects(ext.size() == Ext);
417 template <class ElementType, std::size_t Extent, std::size_t Offset, std::size_t Count>
418 struct calculate_subspan_type
420 using type = span<ElementType, Count != dynamic_extent
422 : (Extent != dynamic_extent ? Extent - Offset : Extent)>;
424 } // namespace details
426 // [span], class template span
427 template <class ElementType, std::size_t Extent>
431 // constants and types
432 using element_type = ElementType;
433 using value_type = std::remove_cv_t<ElementType>;
434 using size_type = std::size_t;
435 using pointer = element_type*;
436 using const_pointer = const element_type*;
437 using reference = element_type&;
438 using const_reference = const element_type&;
439 using difference_type = std::ptrdiff_t;
441 using iterator = details::span_iterator<ElementType>;
442 using reverse_iterator = std::reverse_iterator<iterator>;
444 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
445 static constexpr const size_type extent{Extent};
447 static constexpr size_type extent{Extent};
450 // [span.cons], span constructors, copy, assignment, and destructor
451 template <bool Dependent = false,
452 // "Dependent" is needed to make "std::enable_if_t<Dependent || Extent == 0 || Extent
453 // == dynamic_extent>" SFINAE, since "std::enable_if_t<Extent == 0 || Extent ==
454 // dynamic_extent>" is ill-formed when Extent is greater than 0.
455 class = std::enable_if_t<(Dependent ||
456 details::is_allowed_extent_conversion<0, Extent>::value)>>
457 constexpr span() noexcept : storage_(nullptr, details::extent_type<0>())
460 template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent != dynamic_extent, int> = 0>
461 constexpr explicit span(pointer ptr, size_type count) noexcept : storage_(ptr, count)
463 Expects(count == Extent);
466 template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent == dynamic_extent, int> = 0>
467 constexpr span(pointer ptr, size_type count) noexcept : storage_(ptr, count)
470 template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent != dynamic_extent, int> = 0>
471 constexpr explicit span(pointer firstElem, pointer lastElem) noexcept
472 : storage_(firstElem, narrow_cast<std::size_t>(lastElem - firstElem))
474 Expects(lastElem - firstElem == static_cast<difference_type>(Extent));
477 template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent == dynamic_extent, int> = 0>
478 constexpr span(pointer firstElem, pointer lastElem) noexcept
479 : storage_(firstElem, narrow_cast<std::size_t>(lastElem - firstElem))
482 template <std::size_t N,
483 std::enable_if_t<details::is_allowed_extent_conversion<N, Extent>::value, int> = 0>
484 constexpr span(element_type (&arr)[N]) noexcept
485 : storage_(KnownNotNull{arr}, details::extent_type<N>())
489 class T, std::size_t N,
490 std::enable_if_t<(details::is_allowed_extent_conversion<N, Extent>::value &&
491 details::is_allowed_element_type_conversion<T, element_type>::value),
493 constexpr span(std::array<T, N>& arr) noexcept
494 : storage_(KnownNotNull{arr.data()}, details::extent_type<N>())
497 template <class T, std::size_t N,
499 (details::is_allowed_extent_conversion<N, Extent>::value &&
500 details::is_allowed_element_type_conversion<const T, element_type>::value),
502 constexpr span(const std::array<T, N>& arr) noexcept
503 : storage_(KnownNotNull{arr.data()}, details::extent_type<N>())
506 // NB: the SFINAE on these constructors uses .data() as an incomplete/imperfect proxy for the
507 // requirement on Container to be a contiguous sequence container.
508 template <std::size_t MyExtent = Extent, class Container,
510 MyExtent != dynamic_extent && !details::is_span<Container>::value &&
511 !details::is_std_array<Container>::value &&
512 std::is_pointer<decltype(std::declval<Container&>().data())>::value &&
514 std::remove_pointer_t<decltype(std::declval<Container&>().data())> (*)[],
515 element_type (*)[]>::value,
517 constexpr explicit span(Container& cont) noexcept : span(cont.data(), cont.size())
520 template <std::size_t MyExtent = Extent, class Container,
522 MyExtent == dynamic_extent && !details::is_span<Container>::value &&
523 !details::is_std_array<Container>::value &&
524 std::is_pointer<decltype(std::declval<Container&>().data())>::value &&
526 std::remove_pointer_t<decltype(std::declval<Container&>().data())> (*)[],
527 element_type (*)[]>::value,
529 constexpr span(Container& cont) noexcept : span(cont.data(), cont.size())
533 std::size_t MyExtent = Extent, class Container,
535 MyExtent != dynamic_extent && std::is_const<element_type>::value &&
536 !details::is_span<Container>::value && !details::is_std_array<Container>::value &&
537 std::is_pointer<decltype(std::declval<const Container&>().data())>::value &&
539 std::remove_pointer_t<decltype(std::declval<const Container&>().data())> (*)[],
540 element_type (*)[]>::value,
542 constexpr explicit span(const Container& cont) noexcept : span(cont.data(), cont.size())
546 std::size_t MyExtent = Extent, class Container,
548 MyExtent == dynamic_extent && std::is_const<element_type>::value &&
549 !details::is_span<Container>::value && !details::is_std_array<Container>::value &&
550 std::is_pointer<decltype(std::declval<const Container&>().data())>::value &&
552 std::remove_pointer_t<decltype(std::declval<const Container&>().data())> (*)[],
553 element_type (*)[]>::value,
555 constexpr span(const Container& cont) noexcept : span(cont.data(), cont.size())
558 constexpr span(const span& other) noexcept = default;
560 template <class OtherElementType, std::size_t OtherExtent, std::size_t MyExtent = Extent,
561 std::enable_if_t<(MyExtent == dynamic_extent || MyExtent == OtherExtent) &&
562 details::is_allowed_element_type_conversion<OtherElementType,
563 element_type>::value,
565 constexpr span(const span<OtherElementType, OtherExtent>& other) noexcept
566 : storage_(other.data(), details::extent_type<OtherExtent>(other.size()))
569 template <class OtherElementType, std::size_t OtherExtent, std::size_t MyExtent = Extent,
570 std::enable_if_t<MyExtent != dynamic_extent && OtherExtent == dynamic_extent &&
571 details::is_allowed_element_type_conversion<OtherElementType,
572 element_type>::value,
574 constexpr explicit span(const span<OtherElementType, OtherExtent>& other) noexcept
575 : storage_(other.data(), details::extent_type<OtherExtent>(other.size()))
578 ~span() noexcept = default;
579 constexpr span& operator=(const span& other) noexcept = default;
581 // [span.sub], span subviews
582 template <std::size_t Count>
583 constexpr span<element_type, Count> first() const noexcept
585 Expects(Count <= size());
586 return span<element_type, Count>{data(), Count};
589 template <std::size_t Count>
591 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
593 constexpr span<element_type, Count> last() const noexcept
595 Expects(Count <= size());
596 return span<element_type, Count>{data() + (size() - Count), Count};
599 template <std::size_t Offset, std::size_t Count = dynamic_extent>
601 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
603 constexpr auto subspan() const noexcept ->
604 typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type
606 Expects((size() >= Offset) && (Count == dynamic_extent || (Count <= size() - Offset)));
608 typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type;
609 return type{data() + Offset, Count == dynamic_extent ? size() - Offset : Count};
612 constexpr span<element_type, dynamic_extent> first(size_type count) const noexcept
614 Expects(count <= size());
615 return {data(), count};
618 constexpr span<element_type, dynamic_extent> last(size_type count) const noexcept
620 Expects(count <= size());
621 return make_subspan(size() - count, dynamic_extent, subspan_selector<Extent>{});
624 constexpr span<element_type, dynamic_extent>
625 subspan(size_type offset, size_type count = dynamic_extent) const noexcept
627 return make_subspan(offset, count, subspan_selector<Extent>{});
630 // [span.obs], span observers
631 constexpr size_type size() const noexcept { return storage_.size(); }
633 constexpr size_type size_bytes() const noexcept { return size() * sizeof(element_type); }
635 constexpr bool empty() const noexcept { return size() == 0; }
637 // [span.elem], span element access
639 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
641 constexpr reference operator[](size_type idx) const noexcept
643 Expects(idx < size());
647 constexpr reference front() const noexcept
653 constexpr reference back() const noexcept
656 return data()[size() - 1];
659 constexpr pointer data() const noexcept { return storage_.data(); }
661 // [span.iter], span iterator support
662 constexpr iterator begin() const noexcept
664 const auto data = storage_.data();
666 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
668 return {data, data + size(), data};
671 constexpr iterator end() const noexcept
673 const auto data = storage_.data();
675 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
677 const auto endData = data + storage_.size();
678 return {data, endData, endData};
681 constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
682 constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
685 // Tell MSVC how to unwrap spans in range-based-for
686 constexpr pointer _Unchecked_begin() const noexcept { return data(); }
687 constexpr pointer _Unchecked_end() const noexcept
690 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
692 return data() + size();
697 // Needed to remove unnecessary null check in subspans
703 // this implementation detail class lets us take advantage of the
704 // empty base class optimization to pay for only storage of a single
705 // pointer in the case of fixed-size spans
706 template <class ExtentType>
707 class storage_type : public ExtentType
710 // KnownNotNull parameter is needed to remove unnecessary null check
711 // in subspans and constructors from arrays
712 template <class OtherExtentType>
713 constexpr storage_type(KnownNotNull data, OtherExtentType ext)
714 : ExtentType(ext), data_(data.p)
717 template <class OtherExtentType>
718 constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data)
720 Expects(data || ExtentType::size() == 0);
723 constexpr pointer data() const noexcept { return data_; }
729 storage_type<details::extent_type<Extent>> storage_;
731 // The rest is needed to remove unnecessary null check
732 // in subspans and constructors from arrays
733 constexpr span(KnownNotNull ptr, size_type count) noexcept : storage_(ptr, count) {}
735 template <std::size_t CallerExtent>
736 class subspan_selector
740 template <std::size_t CallerExtent>
741 constexpr span<element_type, dynamic_extent>
742 make_subspan(size_type offset, size_type count, subspan_selector<CallerExtent>) const noexcept
744 const span<element_type, dynamic_extent> tmp(*this);
745 return tmp.subspan(offset, count);
749 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
751 constexpr span<element_type, dynamic_extent>
752 make_subspan(size_type offset, size_type count, subspan_selector<dynamic_extent>) const noexcept
754 Expects(size() >= offset);
756 if (count == dynamic_extent) { return {KnownNotNull{data() + offset}, size() - offset}; }
758 Expects(size() - offset >= count);
759 return {KnownNotNull{data() + offset}, count};
763 #if (defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L))
766 template <class Type, std::size_t Extent>
767 span(Type (&)[Extent]) -> span<Type, Extent>;
769 template <class Type, std::size_t Size>
770 span(std::array<Type, Size>&) -> span<Type, Size>;
772 template <class Type, std::size_t Size>
773 span(const std::array<Type, Size>&) -> span<const Type, Size>;
775 template <class Container,
776 class Element = std::remove_pointer_t<decltype(std::declval<Container&>().data())>>
777 span(Container&) -> span<Element>;
779 template <class Container,
780 class Element = std::remove_pointer_t<decltype(std::declval<const Container&>().data())>>
781 span(const Container&) -> span<Element>;
783 #endif // ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
785 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
786 #if defined(__clang__) && defined(_MSC_VER) && defined(__cplusplus) && (__cplusplus < 201703L)
787 #pragma clang diagnostic push
788 #pragma clang diagnostic ignored "-Wdeprecated" // Bug in clang-cl.exe which raises a C++17 -Wdeprecated warning about this static constexpr workaround in C++14 mode.
789 #endif // defined(__clang__) && defined(_MSC_VER) && defined(__cplusplus) && (__cplusplus < 201703L)
790 template <class ElementType, std::size_t Extent>
791 constexpr const typename span<ElementType, Extent>::size_type span<ElementType, Extent>::extent;
792 #if defined(__clang__) && defined(_MSC_VER) && defined(__cplusplus) && (__cplusplus < 201703L)
793 #pragma clang diagnostic pop
794 #endif // defined(__clang__) && defined(_MSC_VER) && defined(__cplusplus) && (__cplusplus < 201703L)
799 // if we only supported compilers with good constexpr support then
800 // this pair of classes could collapse down to a constexpr function
802 // we should use a narrow_cast<> to go to std::size_t, but older compilers may not see it as
804 // and so will fail compilation of the template
805 template <class ElementType, std::size_t Extent>
806 struct calculate_byte_size : std::integral_constant<std::size_t, sizeof(ElementType) * Extent>
808 static_assert(Extent < dynamic_extent / sizeof(ElementType), "Size is too big.");
811 template <class ElementType>
812 struct calculate_byte_size<ElementType, dynamic_extent>
813 : std::integral_constant<std::size_t, dynamic_extent>
816 } // namespace details
818 // [span.objectrep], views of object representation
819 template <class ElementType, std::size_t Extent>
820 span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
821 as_bytes(span<ElementType, Extent> s) noexcept
823 using type = span<const byte, details::calculate_byte_size<ElementType, Extent>::value>;
826 GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
828 return type{reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
831 template <class ElementType, std::size_t Extent,
832 std::enable_if_t<!std::is_const<ElementType>::value, int> = 0>
833 span<byte, details::calculate_byte_size<ElementType, Extent>::value>
834 as_writable_bytes(span<ElementType, Extent> s) noexcept
836 using type = span<byte, details::calculate_byte_size<ElementType, Extent>::value>;
839 GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
841 return type{reinterpret_cast<byte*>(s.data()), s.size_bytes()};
846 #if defined(_MSC_VER) && !defined(__clang__)
851 #if defined(__GNUC__) && __GNUC__ > 6
852 #pragma GCC diagnostic pop
853 #endif // __GNUC__ > 6
855 #if defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
856 #pragma clang diagnostic pop