[foreign-memaccess+abi] RFR: 8291639: Improve the ability to visualize a MemorySegment in human readable forms [v2]

[Rémi Forax]

On Fri, 26 May 2023 13:06:57 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 with a new target base due to a merge or a rebase. The pull request now contains 29 commits:
> 
>  - Merge master
>  - Fix typos
>  - Clean up toString methods
>  - Add support for MemoryAddress arrays and improve docs
>  - Improve javadoc
>  - Change to IAE if mapper fails
>  - Remove caching
>  - Add tests for initial issue examples
>  - Clean up and optimize
>  - Add support for multidimensional records
>  - ... and 19 more: https://git.openjdk.org/panama-foreign/compare/bee4503b...1d7db589

src/java.base/share/classes/jdk/internal/foreign/LayoutRecordMapper.java line 108:

> 106:             throw new IllegalArgumentException("There is no mapping for " +
> 107:                     missingComponents + " in " + type.getName() +
> 108:                     "(" + String.join(", ", recordComponents.stream().map(RecordComponent::getName).collect(Collectors.joining(", "))) + ")" +

Two joins, String.join and Collectors.joining() ??

src/java.base/share/classes/jdk/internal/foreign/LayoutRecordMapper.java line 123:

> 121:         // where X is the component type.
> 122:         MethodHandle[] handles = componentAndLayoutList.stream()
> 123:                 .map(cl -> {

map() + filter(Object::isNull) should be a flatMap() or a mapMulti()

src/java.base/share/classes/jdk/internal/foreign/LayoutRecordMapper.java line 128:

> 126:                     long byteOffset = layout.byteOffset(pathElement) + offset;
> 127: 
> 128:                     return switch (cl.layout()) {

this switch is too big, there is even a switch in that switch, which makes the code hard to read

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/833#discussion_r1206753921
PR Review Comment: https://git.openjdk.org/panama-foreign/pull/833#discussion_r1206758374
PR Review Comment: https://git.openjdk.org/panama-foreign/pull/833#discussion_r1206756692