Most recent JEP 401 description

[Brian Goetz]

There are no restrictions in the specification.  However, the object 
layout algorithm is already quite complicated, so it is possible there 
will be implementation limitations, at least at first.

On 5/19/2024 12:18 AM, John Bossons wrote:
> Thanks for the confirmation. Good news!
>
> As to 'no restrictions' re size (horizontal - number of fields), fine. 
> But what about depth (vertical - fields that are value objects that in 
> turn contain fields that are value objects etc. all the way down)? No 
> constraint on depth of nesting?
>
>
>
>
>
> On Sat, May 18, 2024 at 8:21 PM Brian Goetz <brian.goetz at oracle.com> 
> wrote:
>
>     Amazingly, yes, value-capable abstract classes can have fields. 
>     We thought for many years this would never be possible; the Great
>     Initialization Alignment (eliminating `vnew` and `withfield` in
>     favor of the `new` and `putfield` approach) made this possible.
>
>     The language imposes no restrictions on the number of fields of
>     value types.  The VM reserves the right to flatten, or not, based
>     on its whims.  One likely whim is that "large" values are usually
>     not worth flattening.  But this is invisible to the user; the
>     semantics are the same whether or not the object is flattened.
>
>     On 5/18/2024 1:24 PM, John Bossons wrote:
>>     Thanks for making this so very clear.
>>
>>     Two questions/issues:
>>     (1) It would be helpful to include more on the properties of
>>     abstract value classes (AVCs) -- perhaps a labelled subsection? A
>>     specific question not dealt with explicitly in the current
>>     version: Can an AVC have an instance field, now that a value
>>     class utilizes the Flexible Constructor Bodies JEP? (The
>>     alternative is  repetition of that field definition and accessor
>>     in every subtype, which is potentially error-prone).
>>     (2) It would also be helpful to include some commentary on
>>     limitations.
>>     Specifically, although it is clear that the purpose is more
>>     efficiently defined SMALL value objects, (a) How big is 'small'?
>>     And (b) will the compiler accept value types of any size, no
>>     matter how deep?
>>
>>     John
>>
>>
>>     Phone:  (416) 450-3584 (cell)
>
>
>
> -- 
> Phone:  (416) 450-3584 (cell)
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