UtkarshSahay123 commented on PR #9015: URL: https://github.com/apache/arrow-rs/pull/9015#issuecomment-3669214607
Thanks for the clarification — that helps. You’re absolutely right that slicing a (Large)StringArray does not change the underlying data buffer, and that the stored offsets remain relative to that buffer. The concern here is not that slicing mutates offsets, but that substring operates on value-relative ranges derived from the offset pairs, while the existing UTF-8 boundary validation reasons about the full buffer. This means the validation is effectively checking a stronger condition than required: that the offset is a UTF-8 boundary in the entire buffer, rather than within the value’s byte range. Conceptually, substring only needs to ensure that the computed offset is a valid UTF-8 boundary relative to the value slice `[offsets[i], offsets[i+1])`. Validating against the full buffer can reject offsets that are value-aligned but not globally meaningful outside that range. That said, I agree that this distinction is subtle, and without a concrete example where the current implementation produces incorrect results, the change may not be justified. I will try to construct a minimal reproducer or add a targeted test demonstrating this behavior. If I’m unable to do so, I’m happy to drop or revise the change. Thanks again for taking the time to review this — I appreciate the guidance. Utkarsh Sahay On Thu, 18 Dec 2025, 1:53 pm Martin Hilton, ***@***.***> wrote: > ***@***.**** commented on this pull request. > > I don't understand why this change is necessary. Slicing a > (Large)StringArray doesn't change the data buffer, so the offsets into > the data buffer also do not change. Do you have an example of a StringArray > where the existing code produces incorrect results? > > — > Reply to this email directly, view it on GitHub > <https://github.com/apache/arrow-rs/pull/9015#pullrequestreview-3591379860>, > or unsubscribe > <https://github.com/notifications/unsubscribe-auth/AYHU2BMNJILFA3HEP4Q7QTD4CJP7PAVCNFSM6AAAAACPMSF64KVHI2DSMVQWIX3LMV43YUDVNRWFEZLROVSXG5CSMV3GSZLXHMZTKOJRGM3TSOBWGA> > . > You are receiving this because you authored the thread.Message ID: > ***@***.***> > -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
