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RFC: add `"mutable arrays"` to `capabilities`

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#845 21 comments 4 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Quiet
Tech stack
python
Domain
documentation

Research direction

Start with the linked array_api.info.capabilities documentation, then read the 21-comment RFC thread to understand the unresolved design questions around a mutability capability. Done means the project reaches a decision on the capability and records the agreed behavior in the Array API standard.

Written by the indexing model from the issue text.

Description

API extension Needs Discussion RFC topic: Inspection

Several parts of the Array API standard assume that array objects are mutable. Some array API implementations (notably JAX) do not support mutating array objects. This has led to array API implementations currently being developed in scipy and sklearn to be entirely unusable in JAX.

Given this, downstream implementations have a few choices:

  1. Use mutability semantics, excluding libraries like JAX.
  2. Avoid mutability semantics to support libraries like JAX.
  3. Explicitly special-case arrays of type jax.numpy.Array, changing the implementation logic for that case.

(1) is a bad choice, because it means JAX will not be supported. (2) is a bad choice, because for libraries like NumPy, it leads to excessive copying of buffers, worsening performance. (3) is a bad choice because it hard-codes the presence of specific implementations in a context that is supposed to be implementation-agnostic.

One way the Array API standard could address this is by adding "mutable arrays" or something similar to the existing capabilities dict. Then downstream implementations could use strategy (3) without special-casing particular implementations.

Dominant language
Python
Stars
281
Forks
52
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