Implement static-sized spans, and handle overload requirements

Note that span is specialized such that a static-sized span only has a single
data member, making it a suitable replacement for  Type (&arg)[Size]  style
variables/parameters.
This commit is contained in:
Chris Robinson 2019-05-27 15:36:10 -07:00
parent f57fedec7f
commit aad49d666a

View File

@ -43,8 +43,45 @@ constexpr const T* data(std::initializer_list<T> list) noexcept
{ return list.begin(); }
template<typename T>
template<typename T, size_t E=static_cast<size_t>(-1)>
class span;
namespace detail_ {
template<typename... Ts>
struct make_void { using type = void; };
template<typename... Ts>
using void_t = typename make_void<Ts...>::type;
template<typename T>
struct is_span : std::false_type { };
template<typename T, size_t E>
struct is_span<span<T,E>> : std::true_type { };
template<typename T>
struct is_std_array : std::false_type { };
template<typename T, size_t N>
struct is_std_array<std::array<T,N>> : std::true_type { };
template<typename T, typename = void>
struct has_size_and_data : std::false_type { };
template<typename T>
struct has_size_and_data<T,
void_t<decltype(al::size(std::declval<T>())), decltype(al::data(std::declval<T>()))>>
: std::true_type { };
} // namespace detail_
#define REQUIRES(...) typename std::enable_if<(__VA_ARGS__),int>::type = 0
#define IS_VALID_CONTAINER(C) \
!detail_::is_span<typename std::remove_cv<C>::type>::value && \
!detail_::is_std_array<typename std::remove_cv<C>::type>::value && \
!std::is_array<typename std::remove_cv<C>::type>::value && \
detail_::has_size_and_data<typename std::remove_cv<C>::type>::value && \
std::is_convertible<typename std::remove_pointer<decltype(al::data(std::declval<C>()))>::type(*)[],element_type(*)[]>::value
template<typename T, size_t E>
class span {
static constexpr size_t dynamic_extent{static_cast<size_t>(-1)};
public:
using element_type = T;
using value_type = typename std::remove_cv<T>::type;
@ -61,22 +98,131 @@ public:
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
static constexpr size_t extent{E};
template<REQUIRES(extent == 0)>
constexpr span() noexcept { }
constexpr span(pointer ptr, index_type /*count*/) : mData{ptr} { }
constexpr span(pointer first, pointer /*last*/) : mData{first} { }
template<size_t N, REQUIRES(extent == N)>
constexpr span(element_type (&arr)[N]) noexcept : span{al::data(arr), al::size(arr)} { }
template<size_t N, REQUIRES(extent == N && std::is_convertible<value_type(*)[],element_type(*)[]>::value)>
constexpr span(std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
template<size_t N, REQUIRES(extent == N && std::is_convertible<value_type(*)[],element_type(*)[]>::value)>
constexpr span(const std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
constexpr span(U &cont) : span{al::data(cont), al::size(cont)} { }
template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
constexpr span(const U &cont) : span{al::data(cont), al::size(cont)} { }
template<typename U, size_t N, REQUIRES(extent == N && std::is_convertible<U(*)[],element_type(*)[]>::value)>
constexpr span(const span<U,N> &span_) noexcept : span{al::data(span_), al::size(span_)} { }
constexpr span(const span&) noexcept = default;
span& operator=(const span &rhs) noexcept = default;
template<typename U, size_t N, REQUIRES(extent == N && std::is_convertible<U(*)[],element_type(*)[]>::value)>
span& operator=(const span<U,N> &rhs) noexcept
{ mData = rhs.data(); return *this; }
constexpr reference front() const { return *mData; }
constexpr reference back() const { return *(mData+E-1); }
constexpr reference operator[](index_type idx) const { return mData[idx]; }
constexpr pointer data() const noexcept { return mData; }
constexpr index_type size() const noexcept { return E; }
constexpr index_type size_bytes() const noexcept { return E * sizeof(value_type); }
constexpr bool empty() const noexcept { return E == 0; }
constexpr iterator begin() const noexcept { return mData; }
constexpr iterator end() const noexcept { return mData+E; }
constexpr const_iterator cbegin() const noexcept { return mData; }
constexpr const_iterator cend() const noexcept { return mData+E; }
constexpr reverse_iterator rbegin() const noexcept { return end(); }
constexpr reverse_iterator rend() const noexcept { return begin(); }
constexpr const_reverse_iterator crbegin() const noexcept { return cend(); }
constexpr const_reverse_iterator crend() const noexcept { return cbegin(); }
template<size_t C>
constexpr span<element_type,C> first() const
{
static_assert(E >= C, "New size exceeds original capacity");
return span<element_type,C>{mData, C};
}
template<size_t C>
constexpr span<element_type,C> last() const
{
static_assert(E >= C, "New size exceeds original capacity");
return span<element_type,C>{mData+(E-C), C};
}
template<size_t O, size_t C, size_t RealC=((C==dynamic_extent) ? E-O : C)>
constexpr span<element_type,RealC> subspan() const
{
static_assert(E >= O, "Offset exceeds extent");
static_assert(E-O >= RealC, "New size exceeds original capacity");
return span<element_type,RealC>{mData+O, RealC};
}
/* NOTE: Can't declare objects of a specialized template class prior to
* defining the specialization. As a result, these methods need to be
* defined later.
*/
constexpr span<element_type,dynamic_extent> first(size_t count) const;
constexpr span<element_type,dynamic_extent> last(size_t count) const;
constexpr span<element_type,dynamic_extent> subspan(size_t offset, size_t count=dynamic_extent) const;
private:
pointer mData{nullptr};
};
template<typename T>
class span<T,static_cast<size_t>(-1)> {
static constexpr size_t dynamic_extent{static_cast<size_t>(-1)};
public:
using element_type = T;
using value_type = typename std::remove_cv<T>::type;
using index_type = size_t;
using difference_type = ptrdiff_t;
using pointer = T*;
using const_pointer = const T*;
using reference = T&;
using const_reference = const T&;
using iterator = pointer;
using const_iterator = const_pointer;
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
static constexpr size_t extent{static_cast<size_t>(-1)};
constexpr span() noexcept = default;
constexpr span(pointer ptr, index_type count) : mData{ptr}, mDataEnd{ptr+count} { }
constexpr span(pointer first, pointer last) : mData{first}, mDataEnd{last} { }
template<size_t N>
constexpr span(element_type (&arr)[N]) noexcept : span{al::data(arr), al::size(arr)} { }
template<size_t N>
template<size_t N, REQUIRES(std::is_convertible<value_type(*)[],element_type(*)[]>::value)>
constexpr span(std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
template<size_t N>
template<size_t N, REQUIRES(std::is_convertible<value_type(*)[],element_type(*)[]>::value)>
constexpr span(const std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
template<typename U>
template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
constexpr span(U &cont) : span{al::data(cont), al::size(cont)} { }
template<typename U>
template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
constexpr span(const U &cont) : span{al::data(cont), al::size(cont)} { }
template<typename U, size_t N, REQUIRES(std::is_convertible<U(*)[],element_type(*)[]>::value)>
constexpr span(const span<U,N> &span_) noexcept : span{al::data(span_), al::size(span_)} { }
constexpr span(const span&) noexcept = default;
span& operator=(const span &rhs) noexcept = default;
template<typename U, size_t N, REQUIRES(std::is_convertible<U(*)[],element_type(*)[]>::value)>
span& operator=(const span<U,N> &rhs) noexcept
{
mData = rhs.data();
mDataEnd = mData + rhs.size();
return *this;
}
constexpr reference front() const { return *mData; }
constexpr reference back() const { return *(mDataEnd-1); }
@ -97,11 +243,25 @@ public:
constexpr const_reverse_iterator crbegin() const noexcept { return cend(); }
constexpr const_reverse_iterator crend() const noexcept { return cbegin(); }
template<size_t C>
constexpr span<element_type,C> first() const
{ return span<element_type,C>{mData, C}; }
constexpr span first(size_t count) const
{ return (count >= size()) ? *this : span{mData, mData+count}; }
template<size_t C>
constexpr span<element_type,C> last() const
{ return span<element_type,C>{mDataEnd-C, C}; }
constexpr span last(size_t count) const
{ return (count >= size()) ? *this : span{mDataEnd-count, mDataEnd}; }
constexpr span subspan(size_t offset, size_t count=static_cast<size_t>(-1)) const
template<size_t O, size_t C>
constexpr span<element_type,C> subspan() const
{ return span<element_type,C>{mData+O, C}; }
constexpr span subspan(size_t offset, size_t count=dynamic_extent) const
{
return (offset >= size()) ? span{} :
(count >= size()-offset) ? span{mData+offset, mDataEnd} :
@ -113,6 +273,31 @@ private:
pointer mDataEnd{nullptr};
};
template<typename T, size_t E>
constexpr inline auto span<T,E>::first(size_t count) const -> span<element_type,dynamic_extent>
{
return (count >= size()) ? span<element_type>{mData, extent} :
span<element_type>{mData, count};
}
template<typename T, size_t E>
constexpr inline auto span<T,E>::last(size_t count) const -> span<element_type,dynamic_extent>
{
return (count >= size()) ? span<element_type>{mData, extent} :
span<element_type>{mData+extent-count, count};
}
template<typename T, size_t E>
constexpr inline auto span<T,E>::subspan(size_t offset, size_t count) const -> span<element_type,dynamic_extent>
{
return (offset >= size()) ? span<element_type>{} :
(count >= size()-offset) ? span<element_type>{mData+offset, mData+extent} :
span<element_type>{mData+offset, mData+offset+count};
}
#undef IS_VALID_CONTAINER
#undef REQUIRES
} // namespace al
#endif /* AL_SPAN_H */