Array

Defined in header <Kokkos_Array.hpp> which is included from <Kokkos_Core.hpp>

Description

Array is a contiguous aggregate owning container storing a fixed size sequence of objects (models holding exactly N elements).

  • This is intended as a replacement for std::array<T, N>.

  • This container is an owning container (the data is embedded in the container itself).

  • This container is an aggregate type with the same semantics as a struct holding a C-style array T[N] as its only non-static data member when N > 0; otherwise, it is an empty container.

  • Unlike a C-style array, it doesn’t decay to T* automatically.

  • As an aggregate type, it can be initialized with aggregate-initialization given at most N initializers that are convertible to T: Kokkos::Array<int, 3> a = { 1, 2, 3 };.

Interface

Changed in version 4.4.0.

template<class T, size_t N>
struct Array

Template Parameters

Template Parameters:

  • T – The type of the element being stored.

  • N – The number of elements being stored.

Public Types

using value_type = T
using pointer = T*
using const_pointer = const T*
using reference = T&
using const_reference = const T&
using size_type = size_t
using difference_type = ptrdiff_t

Public Member Functions

static constexpr bool empty() noexcept
Returns:

N == 0

Since:

noexcept since 5.0

static constexpr size_type size() noexcept
constexpr size_type max_size() const noexcept
Returns:

N

Since:

noexcept since 5.0

template<class iType>
constexpr reference operator[](const iType &i)
template<class iType>
constexpr const_reference operator[](const iType &i) const
Template Parameters:

iType – An integral type or an unscoped enum type.

Returns:

A reference to the i-th element of the array.

constexpr pointer data() noexcept
constexpr const_pointer data() const noexcept
Returns:

A pointer to the first element of the array. If N == 0, the return value is unspecified and not dereferenceable.

Since:

noexcept since 5.0

Deduction Guides

template<class T, class ...U>
Array(T, U...) -> Array<T, 1 + sizeof...(U)>

Non-Member Functions

template<class T, size_t N>
constexpr bool operator==(const Array<T, N> &l, const Array<T, N> &r) noexcept
Returns:

true if and only if ∀ the elements in l and r compare equal.

template<class T, size_t N>
constexpr bool operator!=(const Array<T, N> &l, const Array<T, N> &r) noexcept
Returns:

!(l == r)

template<class T, size_t N>
constexpr kokkos_swap(Array<T, N> &l, Array<T, N> &r) noexcept(N == 0 || is_nothrow_swappable_V<T>)
Returns:

If T is swappable or N == 0, each of the elements in l and r are swapped via kokkos_swap.

template<class T, size_t N>
constexpr Array<remove_cv_t<T>, N> to_array(T (&a)[N])
template<class T, size_t N>
constexpr Array<remove_cv_t<T>, N> to_array(T (&&a)[N])
Returns:

An Array containing the elements copied/moved from a.

template<size_t I, class T, size_t N>
constexpr T &get(Array<T, N> &a) noexcept
template<size_t I, class T, size_t N>
constexpr const T &get(const Array<T, N> &a) noexcept
Returns:

a[I] for (tuple protocol / structured binding support)

template<size_t I, class T, size_t N>
constexpr T &&get(Array<T, N> &&a) noexcept
template<size_t I, class T, size_t N>
constexpr const T &&get(const Array<T, N> &&a) noexcept
Returns:

std::move(a[I]) (for tuple protocol / structured binding support)

template<class T, size_t N>
constexpr T *begin(Array<T, N> &a) noexcept
template<class T, size_t N>
constexpr const T *begin(const Array<T, N> &a) noexcept
Returns:

a.data()

template<class T, size_t N>
constexpr T *end(Array<T, N> &a) noexcept
template<class T, size_t N>
constexpr const T *end(const Array<T, N> &a) noexcept
Returns:

a.data() + a.size()

Deprecated Interface

Deprecated since version 4.4.00.

template<class T = void, size_t N = KOKKOS_INVALID_INDEX, class Proxy = void>
struct Array

  • The primary template was an contiguous aggregate owning container of exactly N elements of type T.

  • This container did not support move semantics.

template<class T, class Proxy>
struct Array<T, 0, Proxy>

  • This container was an empty container.

template<class T>
struct Array<T, KOKKOS_INVALID_INDEX, Array<>::contiguous>

  • This container was a non-owning container.

  • This container had its size determined at construction time.

  • This container could be assigned from any Array<T, N , Proxy>.

  • Assignment did not change the size of this container.

  • This container did not support move semantics.

template<class T>
struct Array<T, KOKKOS_INVALID_INDEX, Array<>::strided>

  • This container was a non-owning container.

  • This container had its size and stride determined at construction time.

  • This container could be assigned from any Array<T, N , Proxy>.

  • Assignment did not change the size or stride of this container.

  • This container did not support move semantics.

template<>
struct Array<void, KOKKOS_INVALID_INDEX, void>

Public Types

type contiguous
type stided

  • This specialization defined the embedded tag types: contiguous and strided.

Examples

#include "Kokkos_Core.hpp"
#include <algorithm>
#include <iostream>
#include <iterator>
#include <memory>
#include <string>
#include <string_view>
#include <type_traits>
#include <utility>

// creates a constexpr array of string_view's
constexpr auto w1n = Kokkos::to_array<std::string_view>(
    {"Mary", "Patricia", "Linda", "Barbara", "Elizabeth", "Jennifer"});
static_assert(
    std::is_same_v<decltype(w1n), const Kokkos::Array<std::string_view, 6>>);
static_assert(w1n.size() == 6 and w1n[5] == "Jennifer");

extern int Main(int /* argc */, char const *const /* argv */[]);
int Main(int /* argc */, char const *const /* argv */[]) {
  Kokkos::ScopeGuard _;

  // Construction uses aggregate initialization
  [[maybe_unused]] Kokkos::Array<int, 3> a1{
      {1, 2, 3}}; // Double-braces required in C++11
                  // and still allowed in C++14 and beyond

  Kokkos::Array<int, 3> a2 = {1, 2, 3}; // Double braces never required after =

  // Output is 3 2 1
  std::reverse_copy(std::data(a2), end(a2),
                    std::ostream_iterator<int>(std::cout, " "));
  std::cout << '\n';

  // Ranged for loop is supported
  // Output is E Ǝ
  Kokkos::Array<std::string, 2> a3{"E", "\u018E"};
  for (const auto &s : a3)
    std::cout << s << ' ';
  std::cout << '\n';

  // Deduction guide for array creation
  [[maybe_unused]] Kokkos::Array a4{3.0, 1.0, 4.0}; // Kokkos::Array<double, 3>

  // Behavior of unspecified elements is the same as with built-in arrays
  [[maybe_unused]] Kokkos::Array<int, 2> a5; // No list init, a5[0] and a5[1]
                                             // are default initialized
  [[maybe_unused]] Kokkos::Array<int, 2>
      a6{}; // List init, both elements are value
            // initialized, a6[0] = a6[1] = 0
  [[maybe_unused]] Kokkos::Array<int, 2> a7{
      1}; // List init, unspecified element is value
          // initialized, a7[0] = 1, a7[1] = 0

  // copies a string literal
  auto t1 = Kokkos::to_array("foo");
  static_assert(t1.size() == 4);

  // deduces both element type and length
  auto t2 = Kokkos::to_array({0, 2, 1, 3});
  static_assert(std::is_same_v<decltype(t2), Kokkos::Array<int, 4>>);

  // deduces length with element type specified
  // implicit conversion happens
  auto t3 = Kokkos::to_array<long>({0, 1, 3});
  static_assert(std::is_same_v<decltype(t3), Kokkos::Array<long, 3>>);

  auto t4 = Kokkos::to_array<std::pair<int, float>>(
      {{3, 0.0f}, {4, 0.1f}, {4, 0.1e23f}});
  static_assert(t4.size() == 3);

  // creates a non-copyable Kokkos::Array
  auto t5 = Kokkos::to_array({std::make_unique<int>(3)});
  static_assert(t5.size() == 1);

  // error: copying multidimensional arrays is not supported
  // char s[2][6] = {"nice", "thing"};
  // auto t6 = Kokkos::to_array(s);

  return 0;
}