File span.hpp
File List > mstl > tcb > span.hpp
Go to the documentation of this file
/*
This is an implementation of C++20's std::span
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/n4820.pdf
*/
// Copyright Tristan Brindle 2018.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file ../../LICENSE_1_0.txt or copy at
// https://www.boost.org/LICENSE_1_0.txt)
#ifndef TCB_SPAN_HPP_INCLUDED
#define TCB_SPAN_HPP_INCLUDED
#include <array>
#include <cstddef>
#include <cstdint>
#include <type_traits>
#ifndef TCB_SPAN_NO_EXCEPTIONS
// Attempt to discover whether we're being compiled with exception support
#if !(defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND))
#define TCB_SPAN_NO_EXCEPTIONS
#endif
#endif
#ifndef TCB_SPAN_NO_EXCEPTIONS
#include <cstdio>
#include <stdexcept>
#endif
// Various feature test macros
#ifndef TCB_SPAN_NAMESPACE_NAME
#define TCB_SPAN_NAMESPACE_NAME tcb
#endif
#if __cplusplus >= 201703L || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
#define TCB_SPAN_HAVE_CPP17
#endif
#if __cplusplus >= 201402L || (defined(_MSVC_LANG) && _MSVC_LANG >= 201402L)
#define TCB_SPAN_HAVE_CPP14
#endif
namespace TCB_SPAN_NAMESPACE_NAME {
// Establish default contract checking behavior
#if !defined(TCB_SPAN_THROW_ON_CONTRACT_VIOLATION) && \
!defined(TCB_SPAN_TERMINATE_ON_CONTRACT_VIOLATION) && \
!defined(TCB_SPAN_NO_CONTRACT_CHECKING)
#if defined(NDEBUG) || !defined(TCB_SPAN_HAVE_CPP14)
#define TCB_SPAN_NO_CONTRACT_CHECKING
#else
#define TCB_SPAN_TERMINATE_ON_CONTRACT_VIOLATION
#endif
#endif
#if defined(TCB_SPAN_THROW_ON_CONTRACT_VIOLATION)
struct contract_violation_error : std::logic_error {
explicit contract_violation_error(const char* msg) : std::logic_error(msg)
{}
};
inline void contract_violation(const char* msg)
{
throw contract_violation_error(msg);
}
#elif defined(TCB_SPAN_TERMINATE_ON_CONTRACT_VIOLATION)
[[noreturn]] inline void contract_violation(const char* /*unused*/)
{
std::terminate();
}
#endif
#if !defined(TCB_SPAN_NO_CONTRACT_CHECKING)
#define TCB_SPAN_STRINGIFY(cond) #cond
#define TCB_SPAN_EXPECT(cond) \
cond ? (void) 0 : contract_violation("Expected " TCB_SPAN_STRINGIFY(cond))
#else
#define TCB_SPAN_EXPECT(cond)
#endif
#if defined(TCB_SPAN_HAVE_CPP17) || defined(__cpp_inline_variables)
#define TCB_SPAN_INLINE_VAR inline
#else
#define TCB_SPAN_INLINE_VAR
#endif
#if defined(TCB_SPAN_HAVE_CPP14) || \
(defined(__cpp_constexpr) && __cpp_constexpr >= 201304)
#define TCB_SPAN_HAVE_CPP14_CONSTEXPR
#endif
#if defined(TCB_SPAN_HAVE_CPP14_CONSTEXPR)
#define TCB_SPAN_CONSTEXPR14 constexpr
#else
#define TCB_SPAN_CONSTEXPR14
#endif
#if defined(TCB_SPAN_HAVE_CPP14_CONSTEXPR) && \
(!defined(_MSC_VER) || _MSC_VER > 1900)
#define TCB_SPAN_CONSTEXPR_ASSIGN constexpr
#else
#define TCB_SPAN_CONSTEXPR_ASSIGN
#endif
#if defined(TCB_SPAN_NO_CONTRACT_CHECKING)
#define TCB_SPAN_CONSTEXPR11 constexpr
#else
#define TCB_SPAN_CONSTEXPR11 TCB_SPAN_CONSTEXPR14
#endif
#if defined(TCB_SPAN_HAVE_CPP17) || defined(__cpp_deduction_guides)
#define TCB_SPAN_HAVE_DEDUCTION_GUIDES
#endif
#if defined(TCB_SPAN_HAVE_CPP17) || defined(__cpp_lib_byte)
#define TCB_SPAN_HAVE_STD_BYTE
#endif
#if defined(TCB_SPAN_HAVE_CPP17) || defined(__cpp_lib_array_constexpr)
#define TCB_SPAN_HAVE_CONSTEXPR_STD_ARRAY_ETC
#endif
#if defined(TCB_SPAN_HAVE_CONSTEXPR_STD_ARRAY_ETC)
#define TCB_SPAN_ARRAY_CONSTEXPR constexpr
#else
#define TCB_SPAN_ARRAY_CONSTEXPR
#endif
#ifdef TCB_SPAN_HAVE_STD_BYTE
using byte = std::byte;
#else
using byte = unsigned char;
#endif
#if defined(TCB_SPAN_HAVE_CPP17)
#define TCB_SPAN_NODISCARD [[nodiscard]]
#else
#define TCB_SPAN_NODISCARD
#endif
TCB_SPAN_INLINE_VAR constexpr std::size_t dynamic_extent = SIZE_MAX;
template <typename ElementType, std::size_t Extent = dynamic_extent>
class span;
namespace detail {
template <typename E, std::size_t S>
struct span_storage {
constexpr span_storage() noexcept = default;
constexpr span_storage(E* p_ptr, std::size_t /*unused*/) noexcept
: ptr(p_ptr)
{}
E* ptr = nullptr;
static constexpr std::size_t size = S;
};
template <typename E>
struct span_storage<E, dynamic_extent> {
constexpr span_storage() noexcept = default;
constexpr span_storage(E* p_ptr, std::size_t p_size) noexcept
: ptr(p_ptr), size(p_size)
{}
E* ptr = nullptr;
std::size_t size = 0;
};
// Reimplementation of C++17 std::size() and std::data()
#if defined(TCB_SPAN_HAVE_CPP17) || \
defined(__cpp_lib_nonmember_container_access)
using std::data;
using std::size;
#else
template <class C>
constexpr auto size(const C& c) -> decltype(c.size())
{
return c.size();
}
template <class T, std::size_t N>
constexpr std::size_t size(const T (&)[N]) noexcept
{
return N;
}
template <class C>
constexpr auto data(C& c) -> decltype(c.data())
{
return c.data();
}
template <class C>
constexpr auto data(const C& c) -> decltype(c.data())
{
return c.data();
}
template <class T, std::size_t N>
constexpr T* data(T (&array)[N]) noexcept
{
return array;
}
template <class E>
constexpr const E* data(std::initializer_list<E> il) noexcept
{
return il.begin();
}
#endif // TCB_SPAN_HAVE_CPP17
#if defined(TCB_SPAN_HAVE_CPP17) || defined(__cpp_lib_void_t)
using std::void_t;
#else
template <typename...>
using void_t = void;
#endif
template <typename T>
using uncvref_t =
typename std::remove_cv<typename std::remove_reference<T>::type>::type;
template <typename>
struct is_span : std::false_type {};
template <typename T, std::size_t S>
struct is_span<span<T, S>> : std::true_type {};
template <typename>
struct is_std_array : std::false_type {};
template <typename T, std::size_t N>
struct is_std_array<std::array<T, N>> : std::true_type {};
template <typename, typename = void>
struct has_size_and_data : std::false_type {};
template <typename T>
struct has_size_and_data<T, void_t<decltype(detail::size(std::declval<T>())),
decltype(detail::data(std::declval<T>()))>>
: std::true_type {};
template <typename C, typename U = uncvref_t<C>>
struct is_container {
static constexpr bool value =
!is_span<U>::value && !is_std_array<U>::value &&
!std::is_array<U>::value && has_size_and_data<C>::value;
};
template <typename T>
using remove_pointer_t = typename std::remove_pointer<T>::type;
template <typename, typename, typename = void>
struct is_container_element_type_compatible : std::false_type {};
template <typename T, typename E>
struct is_container_element_type_compatible<
T, E,
typename std::enable_if<
!std::is_same<
typename std::remove_cv<decltype(detail::data(std::declval<T>()))>::type,
void>::value &&
std::is_convertible<
remove_pointer_t<decltype(detail::data(std::declval<T>()))> (*)[],
E (*)[]>::value
>::type>
: std::true_type {};
template <typename, typename = size_t>
struct is_complete : std::false_type {};
template <typename T>
struct is_complete<T, decltype(sizeof(T))> : std::true_type {};
} // namespace detail
template <typename ElementType, std::size_t Extent>
class span {
static_assert(std::is_object<ElementType>::value,
"A span's ElementType must be an object type (not a "
"reference type or void)");
static_assert(detail::is_complete<ElementType>::value,
"A span's ElementType must be a complete type (not a forward "
"declaration)");
static_assert(!std::is_abstract<ElementType>::value,
"A span's ElementType cannot be an abstract class type");
using storage_type = detail::span_storage<ElementType, Extent>;
public:
// constants and types
using element_type = ElementType;
using value_type = typename std::remove_cv<ElementType>::type;
using size_type = std::size_t;
using difference_type = std::ptrdiff_t;
using pointer = element_type*;
using const_pointer = const element_type*;
using reference = element_type&;
using const_reference = const element_type&;
using iterator = pointer;
using reverse_iterator = std::reverse_iterator<iterator>;
static constexpr size_type extent = Extent;
// [span.cons], span constructors, copy, assignment, and destructor
template <
std::size_t E = Extent,
typename std::enable_if<(E == dynamic_extent || E <= 0), int>::type = 0>
constexpr span() noexcept
{}
TCB_SPAN_CONSTEXPR11 span(pointer ptr, size_type count)
: storage_(ptr, count)
{
TCB_SPAN_EXPECT(extent == dynamic_extent || count == extent);
}
TCB_SPAN_CONSTEXPR11 span(pointer first_elem, pointer last_elem)
: storage_(first_elem, last_elem - first_elem)
{
TCB_SPAN_EXPECT(extent == dynamic_extent ||
last_elem - first_elem ==
static_cast<std::ptrdiff_t>(extent));
}
template <std::size_t N, std::size_t E = Extent,
typename std::enable_if<
(E == dynamic_extent || N == E) &&
detail::is_container_element_type_compatible<
element_type (&)[N], ElementType>::value,
int>::type = 0>
constexpr span(element_type (&arr)[N]) noexcept : storage_(arr, N)
{}
template <typename T, std::size_t N, std::size_t E = Extent,
typename std::enable_if<
(E == dynamic_extent || N == E) &&
detail::is_container_element_type_compatible<
std::array<T, N>&, ElementType>::value,
int>::type = 0>
TCB_SPAN_ARRAY_CONSTEXPR span(std::array<T, N>& arr) noexcept
: storage_(arr.data(), N)
{}
template <typename T, std::size_t N, std::size_t E = Extent,
typename std::enable_if<
(E == dynamic_extent || N == E) &&
detail::is_container_element_type_compatible<
const std::array<T, N>&, ElementType>::value,
int>::type = 0>
TCB_SPAN_ARRAY_CONSTEXPR span(const std::array<T, N>& arr) noexcept
: storage_(arr.data(), N)
{}
template <
typename Container, std::size_t E = Extent,
typename std::enable_if<
E == dynamic_extent && detail::is_container<Container>::value &&
detail::is_container_element_type_compatible<
Container&, ElementType>::value,
int>::type = 0>
constexpr span(Container& cont)
: storage_(detail::data(cont), detail::size(cont))
{}
template <
typename Container, std::size_t E = Extent,
typename std::enable_if<
E == dynamic_extent && detail::is_container<Container>::value &&
detail::is_container_element_type_compatible<
const Container&, ElementType>::value,
int>::type = 0>
constexpr span(const Container& cont)
: storage_(detail::data(cont), detail::size(cont))
{}
constexpr span(const span& other) noexcept = default;
template <typename OtherElementType, std::size_t OtherExtent,
typename std::enable_if<
(Extent == dynamic_extent || OtherExtent == dynamic_extent ||
Extent == OtherExtent) &&
std::is_convertible<OtherElementType (*)[],
ElementType (*)[]>::value,
int>::type = 0>
constexpr span(const span<OtherElementType, OtherExtent>& other) noexcept
: storage_(other.data(), other.size())
{}
~span() noexcept = default;
TCB_SPAN_CONSTEXPR_ASSIGN span&
operator=(const span& other) noexcept = default;
// [span.sub], span subviews
template <std::size_t Count>
TCB_SPAN_CONSTEXPR11 span<element_type, Count> first() const
{
TCB_SPAN_EXPECT(Count <= size());
return {data(), Count};
}
template <std::size_t Count>
TCB_SPAN_CONSTEXPR11 span<element_type, Count> last() const
{
TCB_SPAN_EXPECT(Count <= size());
return {data() + (size() - Count), Count};
}
template <std::size_t Offset, std::size_t Count = dynamic_extent>
using subspan_return_t =
span<ElementType, Count != dynamic_extent
? Count
: (Extent != dynamic_extent ? Extent - Offset
: dynamic_extent)>;
template <std::size_t Offset, std::size_t Count = dynamic_extent>
TCB_SPAN_CONSTEXPR11 subspan_return_t<Offset, Count> subspan() const
{
TCB_SPAN_EXPECT(Offset <= size() &&
(Count == dynamic_extent || Offset + Count <= size()));
return {data() + Offset,
Count != dynamic_extent ? Count : size() - Offset};
}
TCB_SPAN_CONSTEXPR11 span<element_type, dynamic_extent>
first(size_type count) const
{
TCB_SPAN_EXPECT(count <= size());
return {data(), count};
}
TCB_SPAN_CONSTEXPR11 span<element_type, dynamic_extent>
last(size_type count) const
{
TCB_SPAN_EXPECT(count <= size());
return {data() + (size() - count), count};
}
TCB_SPAN_CONSTEXPR11 span<element_type, dynamic_extent>
subspan(size_type offset, size_type count = dynamic_extent) const
{
TCB_SPAN_EXPECT(offset <= size() &&
(count == dynamic_extent || offset + count <= size()));
return {data() + offset,
count == dynamic_extent ? size() - offset : count};
}
// [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);
}
TCB_SPAN_NODISCARD constexpr bool empty() const noexcept
{
return size() == 0;
}
// [span.elem], span element access
TCB_SPAN_CONSTEXPR11 reference operator[](size_type idx) const
{
TCB_SPAN_EXPECT(idx < size());
return *(data() + idx);
}
TCB_SPAN_CONSTEXPR11 reference front() const
{
TCB_SPAN_EXPECT(!empty());
return *data();
}
TCB_SPAN_CONSTEXPR11 reference back() const
{
TCB_SPAN_EXPECT(!empty());
return *(data() + (size() - 1));
}
constexpr pointer data() const noexcept { return storage_.ptr; }
// [span.iterators], span iterator support
constexpr iterator begin() const noexcept { return data(); }
constexpr iterator end() const noexcept { return data() + size(); }
TCB_SPAN_ARRAY_CONSTEXPR reverse_iterator rbegin() const noexcept
{
return reverse_iterator(end());
}
TCB_SPAN_ARRAY_CONSTEXPR reverse_iterator rend() const noexcept
{
return reverse_iterator(begin());
}
private:
storage_type storage_{};
};
#ifdef TCB_SPAN_HAVE_DEDUCTION_GUIDES
/* Deduction Guides */
template <class T, size_t N>
span(T (&)[N])->span<T, N>;
template <class T, size_t N>
span(std::array<T, N>&)->span<T, N>;
template <class T, size_t N>
span(const std::array<T, N>&)->span<const T, N>;
template <class Container>
span(Container&)->span<typename std::remove_reference<
decltype(*detail::data(std::declval<Container&>()))>::type>;
template <class Container>
span(const Container&)->span<const typename Container::value_type>;
#endif // TCB_HAVE_DEDUCTION_GUIDES
template <typename ElementType, std::size_t Extent>
constexpr span<ElementType, Extent>
make_span(span<ElementType, Extent> s) noexcept
{
return s;
}
template <typename T, std::size_t N>
constexpr span<T, N> make_span(T (&arr)[N]) noexcept
{
return {arr};
}
template <typename T, std::size_t N>
TCB_SPAN_ARRAY_CONSTEXPR span<T, N> make_span(std::array<T, N>& arr) noexcept
{
return {arr};
}
template <typename T, std::size_t N>
TCB_SPAN_ARRAY_CONSTEXPR span<const T, N>
make_span(const std::array<T, N>& arr) noexcept
{
return {arr};
}
template <typename Container>
constexpr span<typename std::remove_reference<
decltype(*detail::data(std::declval<Container&>()))>::type>
make_span(Container& cont)
{
return {cont};
}
template <typename Container>
constexpr span<const typename Container::value_type>
make_span(const Container& cont)
{
return {cont};
}
template <typename ElementType, std::size_t Extent>
span<const byte, ((Extent == dynamic_extent) ? dynamic_extent
: sizeof(ElementType) * Extent)>
as_bytes(span<ElementType, Extent> s) noexcept
{
return {reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
}
template <
class ElementType, size_t Extent,
typename std::enable_if<!std::is_const<ElementType>::value, int>::type = 0>
span<byte, ((Extent == dynamic_extent) ? dynamic_extent
: sizeof(ElementType) * Extent)>
as_writable_bytes(span<ElementType, Extent> s) noexcept
{
return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
}
template <std::size_t N, typename E, std::size_t S>
constexpr auto get(span<E, S> s) -> decltype(s[N])
{
return s[N];
}
} // namespace TCB_SPAN_NAMESPACE_NAME
namespace std {
template <typename ElementType, size_t Extent>
class tuple_size<TCB_SPAN_NAMESPACE_NAME::span<ElementType, Extent>>
: public integral_constant<size_t, Extent> {};
template <typename ElementType>
class tuple_size<TCB_SPAN_NAMESPACE_NAME::span<
ElementType, TCB_SPAN_NAMESPACE_NAME::dynamic_extent>>; // not defined
template <size_t I, typename ElementType, size_t Extent>
class tuple_element<I, TCB_SPAN_NAMESPACE_NAME::span<ElementType, Extent>> {
public:
static_assert(Extent != TCB_SPAN_NAMESPACE_NAME::dynamic_extent &&
I < Extent,
"");
using type = ElementType;
};
} // end namespace std
#endif // TCB_SPAN_HPP_INCLUDED