JuliaDiff / JuliaDiff/ChainRulesTestUtils.jl

Support MutableTangent automatically

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mutation
Dominant language
Julia
Stars
50
Forks
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Description

This is a follow up to https://github.com/JuliaDiff/ChainRulesCore.jl/issues/105#issuecomment-1655958008

Right now, using https://github.com/JuliaDiff/ChainRulesCore.jl/pull/626 if you want to test something that MutableTangent that does work e.g.:
test_frule(setfield!, MDemo(3.5)⊢MutableTangent{MDemo}(x=2.0), :x, 5.0)

But if you just do:
test_frule(setfield!, MDemo(3.5), :x, 5.0)
you get an error because the default type we use for structural tangents is the immutable Tangent

We could use the StructuralTangent constructor to automatically chose MutableTangent for mutable primals.
we would want to do that forwardward mode, at least. Not sure if we should also do that in reverse

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Read the linked issue comment and PR 626, then inspect the StructuralTangent and test_frule entry points. Verify that mutable primals select MutableTangent automatically in forward mode, and determine whether reverse mode should receive the same treatment. Done means the provided setfield! example works without an explicit tangent type.

Written by the indexing model from the issue text.

Assessment

Tech stack
julia
Domain
testing
Issue type
Feature
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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