/////////////////////////////////////////////////////////////////////////////// // // Copyright (c) 2015 Microsoft Corporation. All rights reserved. // // This code is licensed under the MIT License (MIT). // // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN // THE SOFTWARE. // /////////////////////////////////////////////////////////////////////////////// // Adapted from // https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/include/gsl/span // and // https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/include/gsl/gsl_util #ifndef mozilla_Span_h #define mozilla_Span_h #include <array> #include <cstddef> #include <cstdint> #include <iterator> #include <limits> #include <string> #include <type_traits> #include <utility> #include "mozilla/Assertions.h" #include "mozilla/Attributes.h" #include "mozilla/Casting.h" #include "mozilla/UniquePtr.h" namespace mozilla { template <typename T, size_t Length> class Array; // Stuff from gsl_util // narrow_cast(): a searchable way to do narrowing casts of values template <class T, class U> inline constexpr T narrow_cast(U&& u) { return static_cast<T>(std::forward<U>(u)); } // end gsl_util // [views.constants], constants // This was -1 in gsl::span, but using size_t for sizes instead of ptrdiff_t // and reserving a magic value that realistically doesn't occur in // compile-time-constant Span sizes makes things a lot less messy in terms of // comparison between signed and unsigned. constexpr const size_t dynamic_extent = std::numeric_limits<size_t>::max(); template <class ElementType, size_t Extent = dynamic_extent> class Span; // implementation details namespace span_details { template <class T> struct is_span_oracle : std::false_type {}; template <class ElementType, size_t Extent> struct is_span_oracle<mozilla::Span<ElementType, Extent>> : std::true_type {}; template <class T> struct is_span : public is_span_oracle<std::remove_cv_t<T>> {}; template <class T> struct is_std_array_oracle : std::false_type {}; template <class ElementType, size_t Extent> struct is_std_array_oracle<std::array<ElementType, Extent>> : std::true_type {}; template <class T> struct is_std_array : public is_std_array_oracle<std::remove_cv_t<T>> {}; template <size_t From, size_t To> struct is_allowed_extent_conversion : public std::integral_constant<bool, From == To || From == mozilla::dynamic_extent || To == mozilla::dynamic_extent> {}; template <class From, class To> struct is_allowed_element_type_conversion : public std::integral_constant< bool, std::is_convertible_v<From (*)[], To (*)[]>> {}; struct SpanKnownBounds {}; template <class SpanT, bool IsConst> class span_iterator { using element_type_ = typename SpanT::element_type; template <class ElementType, size_t Extent> friend class ::mozilla::Span; public: using iterator_category = std::random_access_iterator_tag; using value_type = std::remove_const_t<element_type_>; using difference_type = ptrdiff_t; using reference = std::conditional_t<IsConst, const element_type_, element_type_>&; using pointer = std::add_pointer_t<reference>; constexpr span_iterator() : span_iterator(nullptr, 0, SpanKnownBounds{}) {} constexpr span_iterator(const SpanT* span, typename SpanT::index_type index) : span_(span), index_(index) { MOZ_RELEASE_ASSERT(span == nullptr || (index_ >= 0 && index <= span_->Length())); } private: // For whatever reason, the compiler doesn't like optimizing away the above // MOZ_RELEASE_ASSERT when `span_iterator` is constructed for // obviously-correct cases like `span.begin()` or `span.end()`. We provide // this private constructor for such cases. constexpr span_iterator(const SpanT* span, typename SpanT::index_type index, SpanKnownBounds) : span_(span), index_(index) {} public: // `other` is already correct by construction; we do not need to go through // the release assert above. Put differently, this constructor is effectively // a copy constructor and therefore needs no assertions. friend class span_iterator<SpanT, true>; constexpr MOZ_IMPLICIT span_iterator(const span_iterator<SpanT, false>& other) : span_(other.span_), index_(other.index_) {} constexpr span_iterator<SpanT, IsConst>& operator=( const span_iterator<SpanT, IsConst>&) = default; constexpr reference operator*() const { MOZ_RELEASE_ASSERT(span_); return (*span_)[index_]; } constexpr pointer operator->() const { MOZ_RELEASE_ASSERT(span_); return &((*span_)[index_]); } constexpr span_iterator& operator++() { ++index_; return *this; } constexpr span_iterator operator++(int) { auto ret = *this; ++(*this); return ret; } constexpr span_iterator& operator--() { --index_; return *this; } constexpr span_iterator operator--(int) { auto ret = *this; --(*this); return ret; } constexpr span_iterator operator+(difference_type n) const { auto ret = *this; return ret += n; } constexpr span_iterator& operator+=(difference_type n) { MOZ_RELEASE_ASSERT(span_ && (index_ + n) >= 0 && (index_ + n) <= span_->Length()); index_ += n; return *this; } constexpr span_iterator operator-(difference_type n) const { auto ret = *this; return ret -= n; } constexpr span_iterator& operator-=(difference_type n) { return *this += -n; } constexpr difference_type operator-(const span_iterator& rhs) const { MOZ_RELEASE_ASSERT(span_ == rhs.span_); return index_ - rhs.index_; } constexpr reference operator[](difference_type n) const { return *(*this + n); } constexpr friend bool operator==(const span_iterator& lhs, const span_iterator& rhs) { // Iterators from different spans are uncomparable. A diagnostic assertion // should be enough to check this, though. To ensure that no iterators from // different spans are ever considered equal, still compare them in release // builds. MOZ_DIAGNOSTIC_ASSERT(lhs.span_ == rhs.span_); return lhs.index_ == rhs.index_ && lhs.span_ == rhs.span_; } constexpr friend bool operator!=(const span_iterator& lhs, const span_iterator& rhs) { return !(lhs == rhs); } constexpr friend bool operator<(const span_iterator& lhs, const span_iterator& rhs) { MOZ_DIAGNOSTIC_ASSERT(lhs.span_ == rhs.span_); return lhs.index_ < rhs.index_; } constexpr friend bool operator<=(const span_iterator& lhs, const span_iterator& rhs) { return !(rhs < lhs); } constexpr friend bool operator>(const span_iterator& lhs, const span_iterator& rhs) { return rhs < lhs; } constexpr friend bool operator>=(const span_iterator& lhs, const span_iterator& rhs) { return !(rhs > lhs); } void swap(span_iterator& rhs) { std::swap(index_, rhs.index_); std::swap(span_, rhs.span_); } protected: const SpanT* span_; size_t index_; }; template <class Span, bool IsConst> inline constexpr span_iterator<Span, IsConst> operator+( typename span_iterator<Span, IsConst>::difference_type n, const span_iterator<Span, IsConst>& rhs) { return rhs + n; } template <size_t Ext> class extent_type { public: using index_type = size_t; static_assert(Ext >= 0, "A fixed-size Span must be >= 0 in size."); constexpr extent_type() = default; template <index_type Other> constexpr MOZ_IMPLICIT extent_type(extent_type<Other> ext) { static_assert( Other == Ext || Other == dynamic_extent, "Mismatch between fixed-size extent and size of initializing data."); MOZ_RELEASE_ASSERT(ext.size() == Ext); } constexpr MOZ_IMPLICIT extent_type(index_type length) { MOZ_RELEASE_ASSERT(length == Ext); } constexpr index_type size() const { return Ext; } }; template <> class extent_type<dynamic_extent> { public: using index_type = size_t; template <index_type Other> explicit constexpr extent_type(extent_type<Other> ext) : size_(ext.size()) {} explicit constexpr extent_type(index_type length) : size_(length) {} constexpr index_type size() const { return size_; } private: index_type size_; }; } // namespace span_details /** * Span - slices for C++ * * Span implements Rust's slice concept for C++. It's called "Span" instead of * "Slice" to follow the naming used in C++ Core Guidelines. * * A Span wraps a pointer and a length that identify a non-owning view to a * contiguous block of memory of objects of the same type. Various types, * including (pre-decay) C arrays, XPCOM strings, nsTArray, mozilla::Array, * mozilla::Range and contiguous standard-library containers, auto-convert * into Spans when attempting to pass them as arguments to methods that take * Spans. (Span itself autoconverts into mozilla::Range.) * * Like Rust's slices, Span provides safety against out-of-bounds access by * performing run-time bound checks. However, unlike Rust's slices, Span * cannot provide safety against use-after-free. * * (Note: Span is like Rust's slice only conceptually. Due to the lack of * ABI guarantees, you should still decompose spans/slices to raw pointer * and length parts when crossing the FFI. The Elements() and data() methods * are guaranteed to return a non-null pointer even for zero-length spans, * so the pointer can be used as a raw part of a Rust slice without further * checks.) * * In addition to having constructors (with the support of deduction guides) * that take various well-known types, a Span for an arbitrary type can be * constructed from a pointer and a length or a pointer and another pointer * pointing just past the last element. * * A Span<const char> or Span<const char16_t> can be obtained for const char* * or const char16_t pointing to a zero-terminated string using the * MakeStringSpan() function (which treats a nullptr argument equivalently * to the empty string). Corresponding implicit constructor does not exist * in order to avoid accidental construction in cases where const char* or * const char16_t* do not point to a zero-terminated string. * * Span has methods that follow the Mozilla naming style and methods that * don't. The methods that follow the Mozilla naming style are meant to be * used directly from Mozilla code. The methods that don't are meant for * integration with C++11 range-based loops and with meta-programming that * expects the same methods that are found on the standard-library * containers. For example, to decompose a Span into its parts in Mozilla * code, use Elements() and Length() (as with nsTArray) instead of data() * and size() (as with std::vector). * * The pointer and length wrapped by a Span cannot be changed after a Span has * been created. When new values are required, simply create a new Span. Span * has a method called Subspan() that works analogously to the Substring() * method of XPCOM strings taking a start index and an optional length. As a * Mozilla extension (relative to Microsoft's gsl::span that mozilla::Span is * based on), Span has methods From(start), To(end) and FromTo(start, end) * that correspond to Rust's &slice[start..], &slice[..end] and * &slice[start..end], respectively. (That is, the end index is the index of * the first element not to be included in the new subspan.) * * When indicating a Span that's only read from, const goes inside the type * parameter. Don't put const in front of Span. That is: * size_t ReadsFromOneSpanAndWritesToAnother(Span<const uint8_t> aReadFrom, * Span<uint8_t> aWrittenTo); * * Any Span<const T> can be viewed as Span<const uint8_t> using the function * AsBytes(). Any Span<T> can be viewed as Span<uint8_t> using the function * AsWritableBytes(). * * Note that iterators from different Span instances are uncomparable, even if * they refer to the same memory. This also applies to any spans derived via * Subspan etc. */ template <class ElementType, size_t Extent /* = dynamic_extent */> class Span { public: // constants and types using element_type = ElementType; using value_type = std::remove_cv_t<element_type>; using index_type = size_t; using pointer = element_type*; using reference = element_type&; using iterator = span_details::span_iterator<Span<ElementType, Extent>, false>; using const_iterator = span_details::span_iterator<Span<ElementType, Extent>, true>; using reverse_iterator = std::reverse_iterator<iterator>; using const_reverse_iterator = std::reverse_iterator<const_iterator>; constexpr static const index_type extent = Extent; // [Span.cons], Span constructors, copy, assignment, and destructor // "Dependent" is needed to make "std::enable_if_t<(Dependent || // Extent == 0 || Extent == dynamic_extent)>" SFINAE, // since // "std::enable_if_t<(Extent == 0 || Extent == dynamic_extent)>" is // ill-formed when Extent is neither of the extreme values. /** * Constructor with no args. */ template <bool Dependent = false, class = std::enable_if_t<(Dependent || Extent == 0 || Extent == dynamic_extent)>> constexpr Span() : storage_(nullptr, span_details::extent_type<0>()) {} /** * Constructor for nullptr. */ constexpr MOZ_IMPLICIT Span(std::nullptr_t) : Span() {} /** * Constructor for pointer and length. */ constexpr Span(pointer aPtr, index_type aLength) : storage_(aPtr, aLength) {} /** * Constructor for start pointer and pointer past end. */ constexpr Span(pointer aStartPtr, pointer aEndPtr) : storage_(aStartPtr, std::distance(aStartPtr, aEndPtr)) {} /** * Constructor for pair of Span iterators. */ template <typename OtherElementType, size_t OtherExtent, bool IsConst> constexpr Span( span_details::span_iterator<Span<OtherElementType, OtherExtent>, IsConst> aBegin, span_details::span_iterator<Span<OtherElementType, OtherExtent>, IsConst> aEnd) : storage_(aBegin == aEnd ? nullptr : &*aBegin, aEnd - aBegin) {} /** * Constructor for {iterator,size_t} */ template <typename OtherElementType, size_t OtherExtent, bool IsConst> constexpr Span( span_details::span_iterator<Span<OtherElementType, OtherExtent>, IsConst> aBegin, index_type aLength) : storage_(!aLength ? nullptr : &*aBegin, aLength) {} /** * Constructor for C array. */ template <size_t N> constexpr MOZ_IMPLICIT Span(element_type (&aArr)[N]) : storage_(&aArr[0], span_details::extent_type<N>()) {} // Implicit constructors for char* and char16_t* pointers are deleted in order // to avoid accidental construction in cases where a pointer does not point to // a zero-terminated string. A Span<const char> or Span<const char16_t> can be // obtained for const char* or const char16_t pointing to a zero-terminated // string using the MakeStringSpan() function. // (This must be a template because otherwise it will prevent the previous // array constructor to match because an array decays to a pointer. This only // exists to point to the above explanation, since there's no other // constructor that would match.) template < typename T, typename = std::enable_if_t< std::is_pointer_v<T> && (std::is_same_v<std::remove_const_t<std::decay_t<T>>, char> || std::is_same_v<std::remove_const_t<std::decay_t<T>>, char16_t>)>> Span(T& aStr) = delete; /** * Constructor for std::array. */ template <size_t N, class ArrayElementType = std::remove_const_t<element_type>> constexpr MOZ_IMPLICIT Span(std::array<ArrayElementType, N>& aArr) : storage_(&aArr[0], span_details::extent_type<N>()) {} /** * Constructor for const std::array. */ template <size_t N> constexpr MOZ_IMPLICIT Span( const std::array<std::remove_const_t<element_type>, N>& aArr) : storage_(&aArr[0], span_details::extent_type<N>()) {} /** * Constructor for mozilla::Array. */ template <size_t N, class ArrayElementType = std::remove_const_t<element_type>> constexpr MOZ_IMPLICIT Span(mozilla::Array<ArrayElementType, N>& aArr) : storage_(&aArr[0], span_details::extent_type<N>()) {} /** * Constructor for const mozilla::Array. */ template <size_t N> constexpr MOZ_IMPLICIT Span( const mozilla::Array<std::remove_const_t<element_type>, N>& aArr) : storage_(&aArr[0], span_details::extent_type<N>()) {} /** * Constructor for mozilla::UniquePtr holding an array and length. */ template <class ArrayElementType = std::add_pointer<element_type>> constexpr Span(const mozilla::UniquePtr<ArrayElementType>& aPtr, index_type aLength) : storage_(aPtr.get(), aLength) {} // NB: the SFINAE here uses .data() as a incomplete/imperfect proxy for the // requirement on Container to be a contiguous sequence container. /** * Constructor for standard-library containers. */ template < class Container, class Dummy = std::enable_if_t< !std::is_const_v<Container> && !span_details::is_span<Container>::value && !span_details::is_std_array<Container>::value && std::is_convertible_v<typename Container::pointer, pointer> && std::is_convertible_v<typename Container::pointer, decltype(std::declval<Container>().data())>, Container>> constexpr MOZ_IMPLICIT Span(Container& cont, Dummy* = nullptr) : Span(cont.data(), ReleaseAssertedCast<index_type>(cont.size())) {} /** * Constructor for standard-library containers (const version). */ template < class Container, class = std::enable_if_t< std::is_const_v<element_type> && !span_details::is_span<Container>::value && std::is_convertible_v<typename Container::pointer, pointer> && std::is_convertible_v<typename Container::pointer, decltype(std::declval<Container>().data())>>> constexpr MOZ_IMPLICIT Span(const Container& cont) : Span(cont.data(), ReleaseAssertedCast<index_type>(cont.size())) {} // NB: the SFINAE here uses .Elements() as a incomplete/imperfect proxy for // the requirement on Container to be a contiguous sequence container. /** * Constructor for contiguous Mozilla containers. */ template < class Container, class = std::enable_if_t< !std::is_const_v<Container> && !span_details::is_span<Container>::value && !span_details::is_std_array<Container>::value && std::is_convertible_v<typename Container::value_type*, pointer> && std::is_convertible_v< typename Container::value_type*, decltype(std::declval<Container>().Elements())>>> constexpr MOZ_IMPLICIT Span(Container& cont, void* = nullptr) : Span(cont.Elements(), ReleaseAssertedCast<index_type>(cont.Length())) {} /** * Constructor for contiguous Mozilla containers (const version). */ template < class Container, class = std::enable_if_t< std::is_const_v<element_type> && !span_details::is_span<Container>::value && std::is_convertible_v<typename Container::value_type*, pointer> && std::is_convertible_v< typename Container::value_type*, decltype(std::declval<Container>().Elements())>>> constexpr MOZ_IMPLICIT Span(const Container& cont, void* = nullptr) : Span(cont.Elements(), ReleaseAssertedCast<index_type>(cont.Length())) {} /** * Constructor from other Span. */ constexpr Span(const Span& other) = default; /** * Constructor from other Span. */ constexpr Span(Span&& other) = default; /** * Constructor from other Span with conversion of element type. */ template < class OtherElementType, size_t OtherExtent, class = std::enable_if_t<span_details::is_allowed_extent_conversion< OtherExtent, Extent>::value && span_details::is_allowed_element_type_conversion< OtherElementType, element_type>::value>> constexpr MOZ_IMPLICIT Span(const Span<OtherElementType, OtherExtent>& other) : storage_(other.data(), span_details::extent_type<OtherExtent>(other.size())) {} /** * Constructor from other Span with conversion of element type. */ template < class OtherElementType, size_t OtherExtent, class = std::enable_if_t<span_details::is_allowed_extent_conversion< OtherExtent, Extent>::value && span_details::is_allowed_element_type_conversion< OtherElementType, element_type>::value>> constexpr MOZ_IMPLICIT Span(Span<OtherElementType, OtherExtent>&& other) : storage_(other.data(), span_details::extent_type<OtherExtent>(other.size())) {} ~Span() = default; constexpr Span& operator=(const Span& other) = default; constexpr Span& operator=(Span&& other) = default; // [Span.sub], Span subviews /** * Subspan with first N elements with compile-time N. */ template <size_t Count> constexpr Span<element_type, Count> First() const { MOZ_RELEASE_ASSERT(Count <= size()); return {data(), Count}; } /** * Subspan with last N elements with compile-time N. */ template <size_t Count> constexpr Span<element_type, Count> Last() const { const size_t len = size(); MOZ_RELEASE_ASSERT(Count <= len); return {data() + (len - Count), Count}; } /** * Subspan with compile-time start index and length. */ template <size_t Offset, size_t Count = dynamic_extent> constexpr Span<element_type, Count> Subspan() const { const size_t len = size(); MOZ_RELEASE_ASSERT(Offset <= len && (Count == dynamic_extent || (Offset + Count <= len))); return {data() + Offset, Count == dynamic_extent ? len - Offset : Count}; } /** * Subspan with first N elements with run-time N. */ constexpr Span<element_type, dynamic_extent> First(index_type aCount) const { MOZ_RELEASE_ASSERT(aCount <= size()); return {data(), aCount}; } /** * Subspan with last N elements with run-time N. */ constexpr Span<element_type, dynamic_extent> Last(index_type aCount) const { const size_t len = size(); MOZ_RELEASE_ASSERT(aCount <= len); return {data() + (len - aCount), aCount}; } /** * Subspan with run-time start index and length. */ constexpr Span<element_type, dynamic_extent> Subspan( index_type aStart, index_type aLength = dynamic_extent) const { const size_t len = size(); MOZ_RELEASE_ASSERT(aStart <= len && (aLength == dynamic_extent || (aStart + aLength <= len))); return {data() + aStart, aLength == dynamic_extent ? len - aStart : aLength}; } /** * Subspan with run-time start index. (Rust's &foo[start..]) */ constexpr Span<element_type, dynamic_extent> From(index_type aStart) const { return Subspan(aStart); } /** * Subspan with run-time exclusive end index. (Rust's &foo[..end]) */ constexpr Span<element_type, dynamic_extent> To(index_type aEnd) const { return Subspan(0, aEnd); } /// std::span-compatible method name constexpr auto subspan(index_type aStart, index_type aLength = dynamic_extent) const { return Subspan(aStart, aLength); } /// std::span-compatible method name constexpr auto from(index_type aStart) const { return From(aStart); } /// std::span-compatible method name constexpr auto to(index_type aEnd) const { return To(aEnd); } /** * Subspan with run-time start index and exclusive end index. * (Rust's &foo[start..end]) */ constexpr Span<element_type, dynamic_extent> FromTo(index_type aStart, index_type aEnd) const { MOZ_RELEASE_ASSERT(aStart <= aEnd); return Subspan(aStart, aEnd - aStart); } // [Span.obs], Span observers /** * Number of elements in the span. */ constexpr index_type Length() const { return size(); } /** * Number of elements in the span (standard-libray duck typing version). */ constexpr index_type size() const { return storage_.size(); } /** * Size of the span in bytes. */ constexpr index_type LengthBytes() const { return size_bytes(); } /** * Size of the span in bytes (standard-library naming style version). */ constexpr index_type size_bytes() const { return size() * narrow_cast<index_type>(sizeof(element_type)); } /** * Checks if the the length of the span is zero. */ constexpr bool IsEmpty() const { return empty(); } /** * Checks if the the length of the span is zero (standard-libray duck * typing version). */ constexpr bool empty() const { return size() == 0; } // [Span.elem], Span element access constexpr reference operator[](index_type idx) const { MOZ_RELEASE_ASSERT(idx < storage_.size()); return data()[idx]; } /** * Access element of span by index (standard-library duck typing version). */ constexpr reference at(index_type idx) const { return this->operator[](idx); } constexpr reference operator()(index_type idx) const { return this->operator[](idx); } /** * Pointer to the first element of the span. The return value is never * nullptr, not ever for zero-length spans, so it can be passed as-is * to std::slice::from_raw_parts() in Rust. */ constexpr pointer Elements() const { return data(); } /** * Pointer to the first element of the span (standard-libray duck typing * version). The return value is never nullptr, not ever for zero-length * spans, so it can be passed as-is to std::slice::from_raw_parts() in Rust. */ constexpr pointer data() const { return storage_.data(); } // [Span.iter], Span iterator support iterator begin() const { return {this, 0, span_details::SpanKnownBounds{}}; } iterator end() const { return {this, Length(), span_details::SpanKnownBounds{}}; } const_iterator cbegin() const { return {this, 0, span_details::SpanKnownBounds{}}; } const_iterator cend() const { return {this, Length(), span_details::SpanKnownBounds{}}; } reverse_iterator rbegin() const { return reverse_iterator{end()}; } reverse_iterator rend() const { return reverse_iterator{begin()}; } const_reverse_iterator crbegin() const { return const_reverse_iterator{cend()}; } const_reverse_iterator crend() const { return const_reverse_iterator{cbegin()}; } template <size_t SplitPoint> constexpr std::pair<Span<ElementType, SplitPoint>, Span<ElementType, Extent - SplitPoint>> SplitAt() const { static_assert(Extent != dynamic_extent); static_assert(SplitPoint <= Extent); return {First<SplitPoint>(), Last<Extent - SplitPoint>()}; } constexpr std::pair<Span<ElementType, dynamic_extent>, Span<ElementType, dynamic_extent>> SplitAt(const index_type aSplitPoint) const { MOZ_RELEASE_ASSERT(aSplitPoint <= Length()); return {First(aSplitPoint), Last(Length() - aSplitPoint)}; } constexpr Span<std::add_const_t<ElementType>, Extent> AsConst() const { return {Elements(), Length()}; } private: // this implementation detail class lets us take advantage of the // empty base class optimization to pay for only storage of a single // pointer in the case of fixed-size Spans template <class ExtentType> class storage_type : public ExtentType { public: template <class OtherExtentType> constexpr storage_type(pointer elements, OtherExtentType ext) : ExtentType(ext) // Replace nullptr with aligned bogus pointer for Rust slice // compatibility. See // https://doc.rust-lang.org/std/slice/fn.from_raw_parts.html , data_(elements ? elements : reinterpret_cast<pointer>(alignof(element_type))) { const size_t extentSize = ExtentType::size(); MOZ_RELEASE_ASSERT((!elements && extentSize == 0) || (elements && extentSize != dynamic_extent)); } constexpr pointer data() const { return data_; } private: pointer data_; }; storage_type<span_details::extent_type<Extent>> storage_; }; template <typename T, size_t OtherExtent, bool IsConst> Span(span_details::span_iterator<Span<T, OtherExtent>, IsConst> aBegin, span_details::span_iterator<Span<T, OtherExtent>, IsConst> aEnd) -> Span<std::conditional_t<IsConst, std::add_const_t<T>, T>>; template <typename T, size_t Extent> Span(T (&)[Extent]) -> Span<T, Extent>; template <class Container> Span(Container&) -> Span<typename Container::value_type>; template <class Container> Span(const Container&) -> Span<const typename Container::value_type>; template <typename T, size_t Extent> Span(mozilla::Array<T, Extent>&) -> Span<T, Extent>; template <typename T, size_t Extent> Span(const mozilla::Array<T, Extent>&) -> Span<const T, Extent>; // [Span.comparison], Span comparison operators template <class ElementType, size_t FirstExtent, size_t SecondExtent> inline constexpr bool operator==(const Span<ElementType, FirstExtent>& l, const Span<ElementType, SecondExtent>& r) { return (l.size() == r.size()) && std::equal(l.data(), l.data() + l.size(), r.data()); } template <class ElementType, size_t Extent> inline constexpr bool operator!=(const Span<ElementType, Extent>& l, const Span<ElementType, Extent>& r) { return !(l == r); } template <class ElementType, size_t Extent> inline constexpr bool operator<(const Span<ElementType, Extent>& l, const Span<ElementType, Extent>& r) { return std::lexicographical_compare(l.data(), l.data() + l.size(), r.data(), r.data() + r.size()); } template <class ElementType, size_t Extent> inline constexpr bool operator<=(const Span<ElementType, Extent>& l, const Span<ElementType, Extent>& r) { return !(l > r); } template <class ElementType, size_t Extent> inline constexpr bool operator>(const Span<ElementType, Extent>& l, const Span<ElementType, Extent>& r) { return r < l; } template <class ElementType, size_t Extent> inline constexpr bool operator>=(const Span<ElementType, Extent>& l, const Span<ElementType, Extent>& r) { return !(l < r); } namespace span_details { // if we only supported compilers with good constexpr support then // this pair of classes could collapse down to a constexpr function // we should use a narrow_cast<> to go to size_t, but older compilers may not // see it as constexpr and so will fail compilation of the template template <class ElementType, size_t Extent> struct calculate_byte_size : std::integral_constant<size_t, static_cast<size_t>(sizeof(ElementType) * static_cast<size_t>(Extent))> { }; template <class ElementType> struct calculate_byte_size<ElementType, dynamic_extent> : std::integral_constant<size_t, dynamic_extent> {}; } // namespace span_details // [Span.objectrep], views of object representation /** * View span as Span<const uint8_t>. */ template <class ElementType, size_t Extent> Span<const uint8_t, span_details::calculate_byte_size<ElementType, Extent>::value> AsBytes(Span<ElementType, Extent> s) { return {reinterpret_cast<const uint8_t*>(s.data()), s.size_bytes()}; } /** * View span as Span<uint8_t>. */ template <class ElementType, size_t Extent, class = std::enable_if_t<!std::is_const_v<ElementType>>> Span<uint8_t, span_details::calculate_byte_size<ElementType, Extent>::value> AsWritableBytes(Span<ElementType, Extent> s) { return {reinterpret_cast<uint8_t*>(s.data()), s.size_bytes()}; } /** * View a span of uint8_t as a span of char. */ inline Span<const char> AsChars(Span<const uint8_t> s) { return {reinterpret_cast<const char*>(s.data()), s.size()}; } /** * View a writable span of uint8_t as a span of char. */ inline Span<char> AsWritableChars(Span<uint8_t> s) { return {reinterpret_cast<char*>(s.data()), s.size()}; } /** * Create span from a zero-terminated C string. nullptr is * treated as the empty string. */ constexpr Span<const char> MakeStringSpan(const char* aZeroTerminated) { if (!aZeroTerminated) { return Span<const char>(); } return Span<const char>(aZeroTerminated, std::char_traits<char>::length(aZeroTerminated)); } /** * Create span from a zero-terminated UTF-16 C string. nullptr is * treated as the empty string. */ constexpr Span<const char16_t> MakeStringSpan(const char16_t* aZeroTerminated) { if (!aZeroTerminated) { return Span<const char16_t>(); } return Span<const char16_t>( aZeroTerminated, std::char_traits<char16_t>::length(aZeroTerminated)); } } // namespace mozilla #endif // mozilla_Span_h