8000 Add section on copy-view behaviour and mutability by rgommers · Pull Request #66 · data-apis/array-api · GitHub
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Nov 3, 2020
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Add section on copy-view behaviour and mutability #66

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9153f06
Add section on copy-view behaviour and mutability
rgommers Oct 29, 2020
2427d47
Add note on tracing that may make implementing out= impossible.
rgommers Nov 3, 2020
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Add note on tracing that may make implementing out= impossible.
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@rgommers
rgommers committed Nov 3, 2020
commit 2427d47f2fa290feb74dea2a0b6a92df5c0003f3
15 changes: 9 additions & 6 deletions spec/design_topics/copies_views_and_mutation.md
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Expand Up @@ -57,12 +57,15 @@ The situation with `out=` is slightly different - it's less heavily used, and
easier to avoid. It's also not an optimal API, because it mixes an
"efficiency of implementation" consideration ("you're allowed to do this
inplace") with the semantics of a function ("the output _must_ be placed into
this array). There's alternatives, for example the donated arguments in JAX
or working buffers in LAPACK, that allow the user to express "you _may_
overwrite this data, do whatever is fastest". Given that those alternatives
aren't widely used in array libraries today, this API standard chooses to (a)
leave out `out=`, and (b) not specify another method of reusing arrays that
are no longer needed as buffers.
this array). There are libraries that do some form of tracing or abstract
interpretation over a language that does not support mutation (to make
analysis easier); in those cases implementing `out=` with correct handling of
views may even be impossible to do. There's alternatives, for example the
donated arguments in JAX or working buffers in LAPACK, that allow the user to
express "you _may_ overwrite this data, do whatever is fastest". Given that
those alternatives aren't widely used in array libraries today, this API
standard chooses to (a) leave out `out=`, and (b) not specify another method
of reusing arrays that are no longer needed as buffers.

This leaves the problem of the initial example - with this API standard it
remains possible to write code that will not work the same for all array
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