SmolStrBuilder: move rather than alloc + copy on finish #21194
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Removing unnessecary len checks as well as 1 redundant alloc + copy on finishing a Builder into a SmolStr
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I think i tried this and couldn't produce a benchmark improvement. Do you see better perf with this, e.g. with the format benchmark? Btw this doesn't solve rust-analyzer/smol_str#94 as, iirc that was about the String -> Arc extra allocation. But such an optimisation does make some sense, though I doubt it's worth making a breaking api change for it. A new method + deprecation could avoid this. |
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| SmolStrBuilderRepr::Heap(heap) => Repr::new(heap), | ||
| SmolStrBuilderRepr::Heap(heap) => Repr::Heap(Arc::from(heap.into_boxed_str())), |
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This will allocate more, not less. Arc::from will allocate anyway, so this just has the extra allocation for into_boxed_str().
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As explained in the comment there isn't any actual optimization done here, therefore this is definitely not worth the API breakage. |
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Removing unnessecary len checks as well as 1 redundant alloc + copy on finishing a Builder into a SmolStr.
Browsing the old repo for smolstr i came about an issue that mentioned a redundant alloc + copy when finishing a SmolStrBuilder (rust-analyzer/smol_str#94) by @alexheretic.
The solution passes all tests and skips the conditional tests in the Repr::new(), and as long as the internal String has not too much unused capacity the will skip a reallocation + copy. (into_boxed_str() uses shrink_to_fit)
NOTE: It does change the finish function signature. finish() took a &self so far. This is contrary to what a user would understand from the word finish, imo.
Someone with merging power needs to decide if this change of signature is acceptable.