Enet4/faiss-rs

Dynamically casting the wrapped quantizer when casting a IndexImpl to a IVFScalarQuantizerIndex?

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#100 opened on Sep 4, 2025

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enhancementhelp wanted

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Description

So I'm trying to read an IVFScalarQuantizer index from a file but it seems like IndexImpl::into_ivf_scalar_quantizer allows me to build a IVFScalarQuantizerIndex<IndexImpl>, but then there is no way to downcast the wrapped quantizer into a concrete type like FlatIndex (to get the ConcurrentIndex impl for it).

Thoughts on letting the quantizer also be specified during the conversion?

- pub fn into_ivf_scalar_quantizer(self) -> Result<IVFScalarQuantizerIndexImpl<IndexImpl>>
+ pub fn into_ivf_scalar_quantizer<Q>(self) -> Result<IVFScalarQuantizerIndexImpl<Q>>

This would allow the caller to assume a concrete type for the quantizer, which would then enable other traits like ConcurrentIndex (if the quantizer index is itself a ConcurrentIndex).

Contributor guide

Research direction
Examine the current `into ivf scalar quantizer` implementation and understand how the quantizer is stored. Explore how to make the function generic over the quantizer type while preserving the downcast behavior. Look for existing generic conversion patterns in the crate to model the change.
Tech stack
rust
Domain
developer experience
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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Active
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Clear
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RustGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75