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core(view): warn about the implications of without initializing #569

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core(view): warn about the implications of without initializing #569

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core(view): warn about view of views in a warning box
romintomasetti Aug 28, 2024
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core(view): implications of WithoutInitializing
romintomasetti Aug 28, 2024
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12 changes: 11 additions & 1 deletion docs/source/ProgrammingGuide/View.rst
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Expand Up @@ -97,7 +97,9 @@ Finally, note that virtual functions are technically allowed, but calling them i
6.2.3 Can I make a View of Views?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

NOVICES: THE ANSWER FOR YOU IS "NO." PLEASE SKIP THIS SECTION.
.. warning::

NOVICES: THE ANSWER FOR YOU IS "NO." PLEASE SKIP THIS SECTION.
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A "View of Views" is a special case of View, where the type of each entry is itself a View. It is possible to make this, but before you try, please see below.

Expand Down Expand Up @@ -458,6 +460,14 @@ in a way that reflects how first-touch affinity to threads is desired.
Typically it is sufficient to use the parallel iteration index as the index of the location in the
view to write to.

.. warning::

:cppkokkos:`WithoutInitialization` implies that the destructor of each element of the :cppkokkos:`View` **will not be called**.
For instance, if the :cppkokkos:`View`'s value type is not trivially destructible,
you **should not use** :cppkokkos:`WithoutInitialization` unless you are taking care of calling the destructor manually before the :cppkokkos:`View` deallocates its memory.

The mental model is that whenever placement new is used to call the constructor, the destructor also isn't called before the memory is deallocated but it needs to be called manually.
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Suggestion: maybe spell out what to do in the case of both trivially and non-trivially destructible data types, maybe even including a couple of simple code-snippet examples. Perhaps also mention a couple of typical use cases where someone would want to use a View WithoutInitialization.

The sentence on line 469 is not clear, and is a little redundant with the immediately preceding statements. It may not be necessary if the previous verbiage were sharpened up, with spelled out use cases and an couple of simple examples.


6.4.3 Deep copy and HostMirror
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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