[foreign-memaccess+abi] RFR: 8291639: Improve the ability to visualize a MemorySegment in human readable forms [v18]

[Maurizio Cimadamore]

On Wed, 31 May 2023 12:05:43 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR proposes to add a "Record Mapper" that allows `MemorySegment` instances to be projected onto `Record` types given `GroupLayout` instances.
>> 
>> Here is a simple example of how to use the mapper:
>> 
>> 
>>     private static final GroupLayout POINT_LAYOUT = MemoryLayout.structLayout(
>>             JAVA_INT.withName("x"),
>>             JAVA_INT.withName("y"));
>> 
>>     MemorySegment segment =  MemorySegment.ofArray(new int[]{3, 4});
>> 
>>     Point point = POINT_LAYOUT.recordMapper(Point.class)
>>           .apply(segment); // Point[x=3, y=4]
>> 
>> 
>> I think the implementation can be improved later, for example by de-duplicating handling of arrays and maybe add recursive "un-pealing" of multidimensional arrays.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Clean up code

src/java.base/share/classes/jdk/internal/foreign/LayoutRecordMapper.java line 470:

> 468: 
> 469:         R[] result = (R[]) Array.newInstance(type, Math.toIntExact(count));
> 470:         Spliterator<MemorySegment> spliterator = segment.spliterator(elementLayout);

Using MemorySegment::elements allows you to avoid interacting with the spliterator directly (which I don't think you need here?)

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/833#discussion_r1211604761