RFR: 8369564: Provide a MemorySegment API to read strings with known lengths [v10]

[Maurizio Cimadamore]

On Fri, 21 Nov 2025 14:14:06 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> Liam Miller-Cushon has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Review feedback
>>   
>>   * handle numChars + srcIndex overflow, and add tests
>>   * replace yen with a character that round trips
>
> Latest version looks good to me. Left one last suggestion inline.

> I think overall it makes sense -- I believe @JornVernee proposed something similar in the past. It's true it's inconsistent with other `copy` method and, in hindsight, it would have perhaps been useful to always return a length (given that in other cases length is expressed in "elements" -- either array elements, or elements expressed in a given layout) -- although in the other cases the copy length can usually be computed using a shift operation.

Also, I believe the need for returning a copy length is probably driven by the fact that we have dropped the `MemorySegment::ofString(String, Charset)` view that we originally anticipated. If we had that method, returning a length wouldn't have been as important -- although perhaps, to compensate fully, we would also have needed a view that took a char index and a char length -- e.g. to view a _substring_ as a memory segment.

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PR Comment: https://git.openjdk.org/jdk/pull/28043#issuecomment-3571270973