para/GSL
1
0
Fork 0
mirror of https://github.com/microsoft/GSL.git synced 2024-11-03 17:56:43 -05:00
Code Issues Actions Packages Projects Releases Wiki Activity
9face82309
GSL/include/gsl/span
Dmitry Kobets 9face82309
Remove unnecessary check from size_bytes() (#1105) 
`size_bytes()` returns the span's size in bytes. 
Assuming the span was constructed with an accurate size parameter, the check `size() < dynamic_extent / sizeof(element_type)` isn't required, since `size_t(-1)` (which is `dynamic_extent`) represents the size of the address space, so the number of bytes will never exceed it and in practice won't even come close.
Otherwise, it is not actually feasible to detect cases when the size parameter does not correspond to the dimensions of the underlying data pointer. In these cases, the relationship `size() < dynamic_extent / sizeof(element_type)` is simply one of many ways in which the `size()` could be incorrect, and serves no necessary purpose.

Resolves #1012
2023-05-09 09:05:26 -07:00

843 lines
30 KiB
C++
Raw Blame History

///////////////////////////////////////////////////////////////////////////////
//
// 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.
//
///////////////////////////////////////////////////////////////////////////////
#ifndef GSL_SPAN_H
#define GSL_SPAN_H
#include "assert" // for Expects
#include "byte" // for byte
#include "span_ext" // for span specialization of gsl::at and other span-related extensions
#include "util" // for narrow_cast
#include <array> // for array
#include <cstddef> // for ptrdiff_t, size_t, nullptr_t
#include <iterator> // for reverse_iterator, distance, random_access_...
#include <memory> // for pointer_traits
#include <type_traits> // for enable_if_t, declval, is_convertible, inte...
#if defined(__has_include) && __has_include(<version>)
#include <version>
#endif
#if defined(_MSC_VER) && !defined(__clang__)
#pragma warning(push)
// turn off some warnings that are noisy about our Expects statements
#pragma warning(disable : 4127) // conditional expression is constant
#pragma warning( \
disable : 4146) // unary minus operator applied to unsigned type, result still unsigned
#pragma warning(disable : 4702) // unreachable code
// Turn MSVC /analyze rules that generate too much noise. TODO: fix in the tool.
#pragma warning(disable : 26495) // uninitalized member when constructor calls constructor
#pragma warning(disable : 26446) // parser bug does not allow attributes on some templates
#endif // _MSC_VER
// See if we have enough C++17 power to use a static constexpr data member
// without needing an out-of-line definition
#if !(defined(__cplusplus) && (__cplusplus >= 201703L))
#define GSL_USE_STATIC_CONSTEXPR_WORKAROUND
#endif // !(defined(__cplusplus) && (__cplusplus >= 201703L))
// GCC 7 does not like the signed unsigned missmatch (size_t ptrdiff_t)
// While there is a conversion from signed to unsigned, it happens at
// compiletime, so the compiler wouldn't have to warn indiscriminately, but
// could check if the source value actually doesn't fit into the target type
// and only warn in those cases.
#if defined(__GNUC__) && __GNUC__ > 6
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wsign-conversion"
#endif
namespace gsl
{
// implementation details
namespace details
{
template <class T>
struct is_span_oracle : std::false_type
{
};
template <class ElementType, std::size_t Extent>
struct is_span_oracle<gsl::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, std::size_t Extent>
struct is_std_array_oracle<std::array<ElementType, Extent>> : std::true_type
{
};
template <class T>
struct is_std_array : is_std_array_oracle<std::remove_cv_t<T>>
{
};
template <std::size_t From, std::size_t To>
struct is_allowed_extent_conversion
: std::integral_constant<bool, From == To || To == dynamic_extent>
{
};
template <class From, class To>
struct is_allowed_element_type_conversion
: std::integral_constant<bool, std::is_convertible<From (*)[], To (*)[]>::value>
{
};
template <class Type>
class span_iterator
{
public:
#if defined(__cpp_lib_ranges) || (defined(_MSVC_STL_VERSION) && defined(__cpp_lib_concepts))
using iterator_concept = std::contiguous_iterator_tag;
#endif // __cpp_lib_ranges
using iterator_category = std::random_access_iterator_tag;
using value_type = std::remove_cv_t<Type>;
using difference_type = std::ptrdiff_t;
using pointer = Type*;
using reference = Type&;
#ifdef _MSC_VER
using _Unchecked_type = pointer;
using _Prevent_inheriting_unwrap = span_iterator;
#endif // _MSC_VER
constexpr span_iterator() = default;
constexpr span_iterator(pointer begin, pointer end, pointer current)
: begin_(begin), end_(end), current_(current)
{}
constexpr operator span_iterator<const Type>() const noexcept
{
return {begin_, end_, current_};
}
constexpr reference operator*() const noexcept
{
Expects(begin_ && end_);
Expects(begin_ <= current_ && current_ < end_);
return *current_;
}
constexpr pointer operator->() const noexcept
{
Expects(begin_ && end_);
Expects(begin_ <= current_ && current_ < end_);
return current_;
}
constexpr span_iterator& operator++() noexcept
{
Expects(begin_ && current_ && end_);
Expects(current_ < end_);
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
++current_;
return *this;
}
constexpr span_iterator operator++(int) noexcept
{
span_iterator ret = *this;
++*this;
return ret;
}
constexpr span_iterator& operator--() noexcept
{
Expects(begin_ && end_);
Expects(begin_ < current_);
--current_;
return *this;
}
constexpr span_iterator operator--(int) noexcept
{
span_iterator ret = *this;
--*this;
return ret;
}
constexpr span_iterator& operator+=(const difference_type n) noexcept
{
if (n != 0) Expects(begin_ && current_ && end_);
if (n > 0) Expects(end_ - current_ >= n);
if (n < 0) Expects(current_ - begin_ >= -n);
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
current_ += n;
return *this;
}
constexpr span_iterator operator+(const difference_type n) const noexcept
{
span_iterator ret = *this;
ret += n;
return ret;
}
friend constexpr span_iterator operator+(const difference_type n,
const span_iterator& rhs) noexcept
{
return rhs + n;
}
constexpr span_iterator& operator-=(const difference_type n) noexcept
{
if (n != 0) Expects(begin_ && current_ && end_);
if (n > 0) Expects(current_ - begin_ >= n);
if (n < 0) Expects(end_ - current_ >= -n);
GSL_SUPPRESS(bounds .1)
current_ -= n;
return *this;
}
constexpr span_iterator operator-(const difference_type n) const noexcept
{
span_iterator ret = *this;
ret -= n;
return ret;
}
template <
class Type2,
std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
constexpr difference_type operator-(const span_iterator<Type2>& rhs) const noexcept
{
Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
return current_ - rhs.current_;
}
constexpr reference operator[](const difference_type n) const noexcept
{
return *(*this + n);
}
template <
class Type2,
std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
constexpr bool operator==(const span_iterator<Type2>& rhs) const noexcept
{
Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
return current_ == rhs.current_;
}
template <
class Type2,
std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
constexpr bool operator!=(const span_iterator<Type2>& rhs) const noexcept
{
return !(*this == rhs);
}
template <
class Type2,
std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
constexpr bool operator<(const span_iterator<Type2>& rhs) const noexcept
{
Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
return current_ < rhs.current_;
}
template <
class Type2,
std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
constexpr bool operator>(const span_iterator<Type2>& rhs) const noexcept
{
return rhs < *this;
}
template <
class Type2,
std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
constexpr bool operator<=(const span_iterator<Type2>& rhs) const noexcept
{
return !(rhs < *this);
}
template <
class Type2,
std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
constexpr bool operator>=(const span_iterator<Type2>& rhs) const noexcept
{
return !(*this < rhs);
}
#ifdef _MSC_VER
// MSVC++ iterator debugging support; allows STL algorithms in 15.8+
// to unwrap span_iterator to a pointer type after a range check in STL
// algorithm calls
friend constexpr void _Verify_range(span_iterator lhs, span_iterator rhs) noexcept
{ // test that [lhs, rhs) forms a valid range inside an STL algorithm
Expects(lhs.begin_ == rhs.begin_ // range spans have to match
&& lhs.end_ == rhs.end_ &&
lhs.current_ <= rhs.current_); // range must not be transposed
}
constexpr void _Verify_offset(const difference_type n) const noexcept
{ // test that *this + n is within the range of this call
if (n != 0) Expects(begin_ && current_ && end_);
if (n > 0) Expects(end_ - current_ >= n);
if (n < 0) Expects(current_ - begin_ >= -n);
}
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
constexpr pointer _Unwrapped() const noexcept
{ // after seeking *this to a high water mark, or using one of the
// _Verify_xxx functions above, unwrap this span_iterator to a raw
// pointer
return current_;
}
// Tell the STL that span_iterator should not be unwrapped if it can't
// validate in advance, even in release / optimized builds:
#if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
static constexpr const bool _Unwrap_when_unverified = false;
#else
static constexpr bool _Unwrap_when_unverified = false;
#endif
// clang-format off
GSL_SUPPRESS(con.3) // NO-FORMAT: attribute // TODO: false positive
// clang-format on
constexpr void _Seek_to(const pointer p) noexcept
{ // adjust the position of *this to previously verified location p
// after _Unwrapped
current_ = p;
}
#endif
pointer begin_ = nullptr;
pointer end_ = nullptr;
pointer current_ = nullptr;
template <typename Ptr>
friend struct std::pointer_traits;
};
}} // namespace gsl::details
namespace std
{
template <class Type>
struct pointer_traits<::gsl::details::span_iterator<Type>>
{
using pointer = ::gsl::details::span_iterator<Type>;
using element_type = Type;
using difference_type = ptrdiff_t;
static constexpr element_type* to_address(const pointer i) noexcept { return i.current_; }
};
} // namespace std
namespace gsl { namespace details {
template <std::size_t Ext>
class extent_type
{
public:
using size_type = std::size_t;
constexpr extent_type() noexcept = default;
constexpr explicit extent_type(extent_type<dynamic_extent>);
constexpr explicit extent_type(size_type size) { Expects(size == Ext); }
constexpr size_type size() const noexcept { return Ext; }
private:
#if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
static constexpr const size_type size_ = Ext; // static size equal to Ext
#else
static constexpr size_type size_ = Ext; // static size equal to Ext
#endif
};
template <>
class extent_type<dynamic_extent>
{
public:
using size_type = std::size_t;
template <size_type Other>
constexpr explicit extent_type(extent_type<Other> ext) : size_(ext.size())
{}
constexpr explicit extent_type(size_type size) : size_(size)
{
Expects(size != dynamic_extent);
}
constexpr size_type size() const noexcept { return size_; }
private:
size_type size_;
};
template <std::size_t Ext>
constexpr extent_type<Ext>::extent_type(extent_type<dynamic_extent> ext)
{
Expects(ext.size() == Ext);
}
template <class ElementType, std::size_t Extent, std::size_t Offset, std::size_t Count>
struct calculate_subspan_type
{
using type = span<ElementType, Count != dynamic_extent
? Count
: (Extent != dynamic_extent ? Extent - Offset : Extent)>;
};
} // namespace details
// [span], class template span
template <class ElementType, std::size_t Extent>
class span
{
public:
// constants and types
using element_type = ElementType;
using value_type = std::remove_cv_t<ElementType>;
using size_type = std::size_t;
using pointer = element_type*;
using const_pointer = const element_type*;
using reference = element_type&;
using const_reference = const element_type&;
using difference_type = std::ptrdiff_t;
using iterator = details::span_iterator<ElementType>;
using reverse_iterator = std::reverse_iterator<iterator>;
#if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
static constexpr const size_type extent{Extent};
#else
static constexpr size_type extent{Extent};
#endif
// [span.cons], span constructors, copy, assignment, and destructor
template <bool Dependent = false,
// "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 greater than 0.
class = std::enable_if_t<(Dependent ||
details::is_allowed_extent_conversion<0, Extent>::value)>>
constexpr span() noexcept : storage_(nullptr, details::extent_type<0>())
{}
template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent != dynamic_extent, int> = 0>
constexpr explicit span(pointer ptr, size_type count) noexcept : storage_(ptr, count)
{
Expects(count == Extent);
}
template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent == dynamic_extent, int> = 0>
constexpr span(pointer ptr, size_type count) noexcept : storage_(ptr, count)
{}
template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent != dynamic_extent, int> = 0>
constexpr explicit span(pointer firstElem, pointer lastElem) noexcept
: storage_(firstElem, narrow_cast<std::size_t>(lastElem - firstElem))
{
Expects(lastElem - firstElem == static_cast<difference_type>(Extent));
}
template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent == dynamic_extent, int> = 0>
constexpr span(pointer firstElem, pointer lastElem) noexcept
: storage_(firstElem, narrow_cast<std::size_t>(lastElem - firstElem))
{}
template <std::size_t N,
std::enable_if_t<details::is_allowed_extent_conversion<N, Extent>::value, int> = 0>
constexpr span(element_type (&arr)[N]) noexcept
: storage_(KnownNotNull{arr}, details::extent_type<N>())
{}
template <
class T, std::size_t N,
std::enable_if_t<(details::is_allowed_extent_conversion<N, Extent>::value &&
details::is_allowed_element_type_conversion<T, element_type>::value),
int> = 0>
constexpr span(std::array<T, N>& arr) noexcept
: storage_(KnownNotNull{arr.data()}, details::extent_type<N>())
{}
template <class T, std::size_t N,
std::enable_if_t<
(details::is_allowed_extent_conversion<N, Extent>::value &&
details::is_allowed_element_type_conversion<const T, element_type>::value),
int> = 0>
constexpr span(const std::array<T, N>& arr) noexcept
: storage_(KnownNotNull{arr.data()}, details::extent_type<N>())
{}
// NB: the SFINAE on these constructors uses .data() as an incomplete/imperfect proxy for the
// requirement on Container to be a contiguous sequence container.
template <std::size_t MyExtent = Extent, class Container,
std::enable_if_t<
MyExtent != dynamic_extent && !details::is_span<Container>::value &&
!details::is_std_array<Container>::value &&
std::is_pointer<decltype(std::declval<Container&>().data())>::value &&
std::is_convertible<
std::remove_pointer_t<decltype(std::declval<Container&>().data())> (*)[],
element_type (*)[]>::value,
int> = 0>
constexpr explicit span(Container& cont) noexcept : span(cont.data(), cont.size())
{}
template <std::size_t MyExtent = Extent, class Container,
std::enable_if_t<
MyExtent == dynamic_extent && !details::is_span<Container>::value &&
!details::is_std_array<Container>::value &&
std::is_pointer<decltype(std::declval<Container&>().data())>::value &&
std::is_convertible<
std::remove_pointer_t<decltype(std::declval<Container&>().data())> (*)[],
element_type (*)[]>::value,
int> = 0>
constexpr span(Container& cont) noexcept : span(cont.data(), cont.size())
{}
template <
std::size_t MyExtent = Extent, class Container,
std::enable_if_t<
MyExtent != dynamic_extent && std::is_const<element_type>::value &&
!details::is_span<Container>::value && !details::is_std_array<Container>::value &&
std::is_pointer<decltype(std::declval<const Container&>().data())>::value &&
std::is_convertible<
std::remove_pointer_t<decltype(std::declval<const Container&>().data())> (*)[],
element_type (*)[]>::value,
int> = 0>
constexpr explicit span(const Container& cont) noexcept : span(cont.data(), cont.size())
{}
template <
std::size_t MyExtent = Extent, class Container,
std::enable_if_t<
MyExtent == dynamic_extent && std::is_const<element_type>::value &&
!details::is_span<Container>::value && !details::is_std_array<Container>::value &&
std::is_pointer<decltype(std::declval<const Container&>().data())>::value &&
std::is_convertible<
std::remove_pointer_t<decltype(std::declval<const Container&>().data())> (*)[],
element_type (*)[]>::value,
int> = 0>
constexpr span(const Container& cont) noexcept : span(cont.data(), cont.size())
{}
constexpr span(const span& other) noexcept = default;
template <class OtherElementType, std::size_t OtherExtent, std::size_t MyExtent = Extent,
std::enable_if_t<(MyExtent == dynamic_extent || MyExtent == OtherExtent) &&
details::is_allowed_element_type_conversion<OtherElementType,
element_type>::value,
int> = 0>
constexpr span(const span<OtherElementType, OtherExtent>& other) noexcept
: storage_(other.data(), details::extent_type<OtherExtent>(other.size()))
{}
template <class OtherElementType, std::size_t OtherExtent, std::size_t MyExtent = Extent,
std::enable_if_t<MyExtent != dynamic_extent && OtherExtent == dynamic_extent &&
details::is_allowed_element_type_conversion<OtherElementType,
element_type>::value,
int> = 0>
constexpr explicit span(const span<OtherElementType, OtherExtent>& other) noexcept
: storage_(other.data(), details::extent_type<OtherExtent>(other.size()))
{}
~span() noexcept = default;
constexpr span& operator=(const span& other) noexcept = default;
// [span.sub], span subviews
template <std::size_t Count>
constexpr span<element_type, Count> first() const noexcept
{
Expects(Count <= size());
return span<element_type, Count>{data(), Count};
}
template <std::size_t Count>
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
constexpr span<element_type, Count> last() const noexcept
{
Expects(Count <= size());
return span<element_type, Count>{data() + (size() - Count), Count};
}
template <std::size_t Offset, std::size_t Count = dynamic_extent>
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
constexpr auto subspan() const noexcept ->
typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type
{
Expects((size() >= Offset) && (Count == dynamic_extent || (Count <= size() - Offset)));
using type =
typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type;
return type{data() + Offset, Count == dynamic_extent ? size() - Offset : Count};
}
constexpr span<element_type, dynamic_extent> first(size_type count) const noexcept
{
Expects(count <= size());
return {data(), count};
}
constexpr span<element_type, dynamic_extent> last(size_type count) const noexcept
{
Expects(count <= size());
return make_subspan(size() - count, dynamic_extent, subspan_selector<Extent>{});
}
constexpr span<element_type, dynamic_extent>
subspan(size_type offset, size_type count = dynamic_extent) const noexcept
{
return make_subspan(offset, count, subspan_selector<Extent>{});
}
// [span.obs], span observers
constexpr size_type size() const noexcept { return storage_.size(); }
constexpr size_type size_bytes() const noexcept { return size() * sizeof(element_type); }
constexpr bool empty() const noexcept { return size() == 0; }
// [span.elem], span element access
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
constexpr reference operator[](size_type idx) const noexcept
{
Expects(idx < size());
return data()[idx];
}
constexpr reference front() const noexcept
{
Expects(size() > 0);
return data()[0];
}
constexpr reference back() const noexcept
{
Expects(size() > 0);
return data()[size() - 1];
}
constexpr pointer data() const noexcept { return storage_.data(); }
// [span.iter], span iterator support
constexpr iterator begin() const noexcept
{
const auto data = storage_.data();
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
return {data, data + size(), data};
}
constexpr iterator end() const noexcept
{
const auto data = storage_.data();
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
const auto endData = data + storage_.size();
return {data, endData, endData};
}
constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
#ifdef _MSC_VER
// Tell MSVC how to unwrap spans in range-based-for
constexpr pointer _Unchecked_begin() const noexcept { return data(); }
constexpr pointer _Unchecked_end() const noexcept
{
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
return data() + size();
}
#endif // _MSC_VER
private:
// Needed to remove unnecessary null check in subspans
struct KnownNotNull
{
pointer p;
};
// 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:
// KnownNotNull parameter is needed to remove unnecessary null check
// in subspans and constructors from arrays
template <class OtherExtentType>
constexpr storage_type(KnownNotNull data, OtherExtentType ext)
: ExtentType(ext), data_(data.p)
{}
template <class OtherExtentType>
constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data)
{
Expects(data || ExtentType::size() == 0);
}
constexpr pointer data() const noexcept { return data_; }
private:
pointer data_;
};
storage_type<details::extent_type<Extent>> storage_;
// The rest is needed to remove unnecessary null check
// in subspans and constructors from arrays
constexpr span(KnownNotNull ptr, size_type count) noexcept : storage_(ptr, count) {}
template <std::size_t CallerExtent>
class subspan_selector
{
};
template <std::size_t CallerExtent>
constexpr span<element_type, dynamic_extent>
make_subspan(size_type offset, size_type count, subspan_selector<CallerExtent>) const noexcept
{
const span<element_type, dynamic_extent> tmp(*this);
return tmp.subspan(offset, count);
}
// clang-format off
GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
// clang-format on
constexpr span<element_type, dynamic_extent>
make_subspan(size_type offset, size_type count, subspan_selector<dynamic_extent>) const noexcept
{
Expects(size() >= offset);
if (count == dynamic_extent) { return {KnownNotNull{data() + offset}, size() - offset}; }
Expects(size() - offset >= count);
return {KnownNotNull{data() + offset}, count};
}
};
#if (defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L))
// Deduction Guides
template <class Type, std::size_t Extent>
span(Type (&)[Extent]) -> span<Type, Extent>;
template <class Type, std::size_t Size>
span(std::array<Type, Size>&) -> span<Type, Size>;
template <class Type, std::size_t Size>
span(const std::array<Type, Size>&) -> span<const Type, Size>;
template <class Container,
class Element = std::remove_pointer_t<decltype(std::declval<Container&>().data())>>
span(Container&) -> span<Element>;
template <class Container,
class Element = std::remove_pointer_t<decltype(std::declval<const Container&>().data())>>
span(const Container&) -> span<Element>;
#endif // ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
#if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
template <class ElementType, std::size_t Extent>
constexpr const typename span<ElementType, Extent>::size_type span<ElementType, Extent>::extent;
#endif
namespace 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 std::size_t, but older compilers may not see it as
// constexpr
// and so will fail compilation of the template
template <class ElementType, std::size_t Extent>
struct calculate_byte_size : std::integral_constant<std::size_t, sizeof(ElementType) * Extent>
{
static_assert(Extent < dynamic_extent / sizeof(ElementType), "Size is too big.");
};
template <class ElementType>
struct calculate_byte_size<ElementType, dynamic_extent>
: std::integral_constant<std::size_t, dynamic_extent>
{
};
} // namespace details
// [span.objectrep], views of object representation
template <class ElementType, std::size_t Extent>
span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
as_bytes(span<ElementType, Extent> s) noexcept
{
using type = span<const byte, details::calculate_byte_size<ElementType, Extent>::value>;
// clang-format off
GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
// clang-format on
return type{reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
}
template <class ElementType, std::size_t Extent,
std::enable_if_t<!std::is_const<ElementType>::value, int> = 0>
span<byte, details::calculate_byte_size<ElementType, Extent>::value>
as_writable_bytes(span<ElementType, Extent> s) noexcept
{
using type = span<byte, details::calculate_byte_size<ElementType, Extent>::value>;
// clang-format off
GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
// clang-format on
return type{reinterpret_cast<byte*>(s.data()), s.size_bytes()};
}
} // namespace gsl
#if defined(_MSC_VER) && !defined(__clang__)
#pragma warning(pop)
#endif // _MSC_VER
#if defined(__GNUC__) && __GNUC__ > 6
#pragma GCC diagnostic pop
#endif // __GNUC__ > 6
#endif // GSL_SPAN_H
Reference in New Issue View Git Blame Copy Permalink