Memory layout benefits of inline classes

Swaranga Sarma sarma.swaranga at
Sun May 3 08:40:47 UTC 2020

Did not see a response on this hence trying again. If this is too soon in
the project for such questions or if folks are too busy please let me know
- it is perfectly understandable.


On Mon, Apr 27, 2020 at 12:44 AM Swaranga Sarma <sarma.swaranga at>

> The examples of the benefits of inline classes that I have seen in demos
> are things like high allocation of data classes in a tight loop. I was
> trying to understand how some of our existing code may benefit by using
> inline classes which is different from the examples seen. I have the
> following questions:
> 1. Optional: If we have a nullable members in a class, we would like to
> return an Optional<T> in the accessor for that member unless we have a
> reason to reduce the allocation. I recall somewhere that Optional might be
> an inline type in the future and this concern may no longer be valid. Is my
> understanding correct?
> 2. CompletableFuture: Similar to Optional, is this a candidate for
> potentially turning into an inline type?
> 3. Regular data classes: In a lot of our code bases, we have data classes
> that look like:
> class Identifier {
>   final @NonNull Name name;
>   final @NonNull Id id;
> }
> class Name {
>   final @NonNull String value;
> }
> class Id {
>   final @NonNull String value;
> }
> We create instances like these and pass these around to other methods.
> Those methods access the necessary values using the access methods like
> or These classes are
> probably good candidates for migrating to records. But I was also
> interested to understand if we also made them inline classes what memory
> layout benefits would we get. Would the pointer de-referencing problem go
> away in such cases?
> To put it in another way, most of our data classes boil down to Strings,
> and assuming String will not become an inline type, would there be any
> memory-layout benefits of making such classes inline?
> Regards
> Swaranga

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