Space Accessibility
===================

.. role::cpp(code)
    :language: cpp

.. _ExecutionSpace: execution_spaces.html#executionspaceconcept

.. |ExecutionSpace| replace:: ``ExecutionSpace``

.. _MemorySpace: memory_spaces.html#memoryspaceconcept

.. |MemorySpace| replace:: ``MemorySpace``

``Kokkos::SpaceAccessibility<>`` is a traits class template that takes an |ExecutionSpace|_ type or |MemorySpace|_ type as the first template argument and a |MemorySpace|_ type as the second type and expresses details about the relationship between those entities. Given memory space types ``MSp1`` and ``MSp2`` and an execution space type ``Ex``, the following expressions will be valid with the specified meaning:

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.. code-block:: cpp
    
    Kokkos::SpaceAccessibility<Ex, MSp1>::accessible

A compile-time value convertible to ``bool`` guaranteed to be ``true`` if and only if accessing memory allocated by an instance of ``MSp1`` from a thread of execution provided by an instance of ``Ex`` (e.g., within a parallel pattern launched on an instance of ``Ex``) is well-defined and valid within the Kokkos programming model for *all* instances of ``Ex`` and *all* instances of ``MSp1``.

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.. code-block:: cpp
    
    Kokkos::SpaceAccessibility<MSp1, MSp2>::accessible

Equivalent to ``Kokkos::SpaceAccessibility<MSp1::execution_space, MSp2>::accessible``.

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.. code-block:: cpp
    
    Kokkos::SpaceAccessibility<MSp1, MSp2>::assignable

.. _KokkosView: view/view.html

.. |KokkosView| replace:: ``Kokkos::View``

A compile-time value convertible to ``bool`` guaranteed to be ``true`` if and only if it is valid within the Kokkos programming model to assign values from  any (otherwise valid) instance of |KokkosView|_ type ``V2`` (with ``std::is_same<V2::memory_space, MSp2>::value`` equal to ``true``) to references retrieved from any (otherwise valid) instance of a ``View`` type ``V1`` (with ``std::is_same<V1::memory_space, MSp1>::value`` equal to ``true``).

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.. code-block:: cpp
    
    Kokkos::SpaceAccessibility<Ex, MSp1>::assignable

Equivalent to ``Kokkos::SpaceAccessibility<Ex::memory_space, MSp1>::assignable``.

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.. code-block:: cpp
    
    Kokkos::SpaceAccessibility<MSp1, MSp2>::deepcopy

.. _KokkosDeepCopy: view/deep_copy.html

.. |KokkosDeepCopy| replace:: ``Kokkos::deep_copy``

A compile-time value convertible to ``bool`` guaranteed to be ``true`` if and only if it is valid within the Kokkos programming model to |KokkosDeepCopy|_ from any (otherwise valid) instance of |KokkosView|_ type ``V2`` (with ``std::is_same<V2::memory_space, MSp2>::value`` equal to ``true``) to any (otherwise valid and otherwise compatible) instance of a ``View`` type ``V1`` (with ``std::is_same<V1::memory_space, MSp1>::value`` equal to ``true``).  In other words, if ``v2`` is a valid instance of ``V2`` and ``v1`` is a valid instance of ``V1`` (with shape and other attributes otherwise compatible with ``v2``), the following expression will be well-defined and valid in the Kokkos programming model:

.. code-block:: cpp
    
    Kokkos::deep_copy(v1, v2);

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.. code-block:: cpp
    
    Kokkos::SpaceAccessibility<Ex, MSp1>::deepcopy

Equivalent to ``Kokkos::SpaceAccessibility<Ex::memory_space, MSp1>::deepcopy``.

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Additionally, the following nested type names will be defined:

.. code-block:: cpp
    
    Kokkos::SpaceAccessibility<Ex, MSp1>::space

An "intercessory" memory space that should be used to deep copy memory for access by any instance of ``Ex``. Formally, a type meeting the requirements of ``Kokkos::Device`` with the following expressions all ``true`` at compile-time:

* ``Kokkos::SpaceAccessibility<Ex, Kokkos::SpaceAccessibility<Ex, MSp1>::space::memory_space>::accessible``
* ``Kokkos::SpaceAccessibility<Kokkos::SpaceAccessibility<Ex, MSp1>::space::memory_space, MSp1>::deepcopy``
* ``Kokkos::SpaceAccessibility<Ex, Kokkos::SpaceAccessibility<Ex, MSp1>::space::memory_space>::deepcopy``

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.. code-block:: cpp
    
    Kokkos::SpaceAccessibility<MSp1, MSp2>::space

Equivalent to ``Kokkos::SpaceAccessibility<MSp1::execution_space, MSp2>::space``.