[foreign-memaccess+abi] RFR: 8291639: Improve the ability to visualize a MemorySegment in human readable forms [v3]

[Glavo]

On Fri, 26 May 2023 16:05:50 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:
> 
>   Assert the invariant the typ is not Record itself

src/java.base/share/classes/jdk/internal/foreign/LayoutRecordMapper.java line 312:

> 310:             var mt = MethodType.methodType(type, MemorySegment.class);
> 311:             // Fold the many identical MemorySegment arguments into a single argument
> 312:             ctor = MethodHandles.permuteArguments(ctor, mt, IntStream.range(0, handles.length)

What is the special meaning of using `IntStream`? Why not `new int[handles.length]`?

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/833#discussion_r1207159151