Add `SplitAt`, `derive(SplitAt)` #2433

jswrenn · 2025-03-10T19:07:32Z

Makes progress towards #1290.

src/lib.rs

src/pointer/inner.rs

src/lib.rs

src/pointer/inner.rs

src/pointer/ptr.rs

src/util/mod.rs

src/lib.rs

src/pointer/inner.rs

src/lib.rs

src/util/mod.rs

src/lib.rs

zerocopy-derive/src/lib.rs

src/lib.rs

joshlf · 2025-03-24T16:25:48Z

@kupiakos I know you had an interest in this regarding #1289. Let us know if this API (specifically, the SplitAt trait and its methods) looks like it'd support your use case? (Though I'm not sure if you actually had a specific use case or were just generally interested in the problem)

codecov-commenter · 2025-03-24T19:09:14Z

Codecov Report

Attention: Patch coverage is 96.56566% with 17 lines in your changes missing coverage. Please review.

Project coverage is 90.69%. Comparing base (079fe9c) to head (52751cd).
Report is 41 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib.rs	93.75%	11 Missing ⚠️
src/util/mod.rs	96.11%	4 Missing ⚠️
src/pointer/inner.rs	99.04%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2433      +/-   ##
==========================================
+ Coverage   90.38%   90.69%   +0.31%     
==========================================
  Files          18       18              
  Lines        7287     7714     +427     
==========================================
+ Hits         6586     6996     +410     
- Misses        701      718      +17

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This derivable trait provides generalized splitting for slice DSTs. Splitting a DST `T` produces a pair `(T, [T::Elem])`, where `T::Elem` is the element type of `T`'s trailing slice. We expose this functionality as a derivable trait, so as to not violate the privacy of the trailing slice. Makes progress towards #1290.

kupiakos · 2025-03-28T01:08:21Z

actually had a specific use case

IIRC, our original use case is also solved with FromBytes::ref_from_prefix_with_elems. How we ended up implementing in 0.7 was the usual way when DSTs don't work out: a struct with fields pointing to the header and dynamic tail. It was fine because we only needed to FromBytes, not construct an owned version.

In any case, this would also make this use case when using DSTs much less fallible.

jswrenn force-pushed the generalized-splits branch from c83d465 to b194be4 Compare March 13, 2025 23:26

joshlf requested changes Mar 13, 2025

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jswrenn force-pushed the generalized-splits branch 2 times, most recently from 7955ba1 to a7a8bba Compare March 17, 2025 18:55

joshlf requested changes Mar 17, 2025

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jswrenn force-pushed the generalized-splits branch from a7a8bba to 66c7ab9 Compare March 17, 2025 19:07

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