Array fields in value objects

[John Bossons]

Thanks for the clarification.

Maybe this is a suggestion for a future JEP (flattening of immutable
arrays)? Emphasis on "future".

John

On Mon, May 19, 2025 at 2:21 PM Brian Goetz <brian.goetz at oracle.com> wrote:

> Arrays are always identity objects; JEP 401 will not change this.
> PostCodeCA can be flattened into a single object reference, which is still
> plenty useful but it won’t flatten the underlying array.
>
> > On May 19, 2025, at 2:15 PM, John Bossons <jbossons at gmail.com> wrote:
> >
> > The current version of JEP 401 describes the potential flattening of
> value object array elements, but leaves unspecified the treatment of value
> object fields that are themselves (immutable) arrays. Some questions:
> >
> > 1) Is a primitive array field (a field that is an array of primitives)
> necessarily accessed by reference (like an identity object) or can it be
> accessed as a bit vector (like a scalar primitive)?
> > Example (fixed char array length):
> > value class PostCodeCA {
> >     char[] codeValue;  // 6-char code, Ascii letter/number chars, could
> store as byte[]
> >     PostCodeCA(String s) {
> >     codeValue = s.toCharArray();
> >     // validation code, inter alia checks length == 6
> >     }
> >     ...  // Note that array elements are immutable because private
> > }
> > Can a PostCodeCA instance be stored as a bit vector, avoiding the
> indirection of a String reference?
> >
> > 2) Can the following be flattened (apart from the inescapable String
> ref)?
> > value record AddressCA { String streetAddress, enum provCA, PostCodeCA
> zipCode }
> > Note that use of the PostCodeCA class ensures the zipCode value is
> immutable.
> >
> > 3) Does it matter if an array field is of varying length?
> > Example:
> > value class CampaignArea {
> >     int areaID;
> >     PostCodeCA[] zipCodes;  // varying array length, again immutable
> because private
> >     CampaignArea(int areaID, List<PostCodeCA> zipCodes) { ... }
> >     ...
> > }
> > Does this class definition potentially permit flattening of a
> CampaignArea instance?
> >
> > This isn't just about strings, but they illustrate the issue as well as
> the potential. Also, it would be useful if this could be clarified in the
> JEP 401 text.
> >
> > John
> >
> > --
> > Phone:  (416) 450-3584 (cell)
>
>

-- 
Phone:  (416) 450-3584 (cell)
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