RFR: 8308645: Javadoc of FFM API needs to be refreshed [v4]

[Maurizio Cimadamore]

On Thu, 1 Jun 2023 19:25:38 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/foreign/MemoryLayout.java line 645:
>> 
>>> 643:      * is 1. As such, regardless of its size, in the absence of an {@linkplain #withByteAlignment(long) explicit}
>>> 644:      * alignment constraint, a padding layout does not affect the alignment constraint of the group or sequence layout
>>> 645:      * it is nested into.
>> 
>> It is possible to override the alignment constraints of group and sequence layouts, so maybe this should say _natural alignment_.
>> Suggestion:
>> 
>>      * alignment constraint, a padding layout does not affect the natural alignment of the group or sequence layout
>>      * it is nested into.
>
> On a related note: should we even allow sequences of padding layouts?

I let sequence of padding slide on the basis that groups of padding are allowed. But it's a somewhat arbitrary line. That said, we do use stuff like that in jextract, where we model types we don't support (or bitfields) as padding. I think starting to ban padding in certain places would result in a less compositional API - and perhaps tools would have to workaround some of these limitations.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14098#discussion_r1213672976