[records] Compile-time constants can be used in local classes static members but cannot be used in records

[Mateusz Romanowski]

Hi Tagir,
Sorry for being flippant earlier.

My concern is orthogonal to const-expressiveness.
It just seems wrong to see a source code where instance method's local
variable value is assigned into a static constant..

Another aspect for consideration in the new nesting story..

W dniu czwartek, 30 stycznia 2020 Tagir Valeev <amaembo at gmail.com>
napisał(a):
>
>
> чт, 30 янв. 2020 г., 0:46 Mateusz Romanowski <romanowski.mateusz at gmail.com
>:
>>
>> Hi Alex et al.,
>>
>> How would we understand an up-level `final Object lock = new Object();`
>> then?
>
> Constant expressions are strictly defined by spec (15.28). This is not
compile time constant.
> With best regards,
> Tagir Valeev
>>
>> Should we perhaps resurrect C-like `static final` variables inside
methods
>> to allow static nested non-constexpr variables?
>>
>> /Mateusz
>>
>>
>> W dniu środa, 29 stycznia 2020 Alex Buckley <alex.buckley at oracle.com>
>> napisał(a):
>> > Note that the up-level variable in this case -- `final int x = 2;` --
is
>> a constant variable, but not a static constant variable (or a static
member
>> of anything). Still, the simple name `x` is in scope in the body of
nested
>> {class, record} X, and counts as a constant expression, so RecordTest
>> should compile in 15 once when JDK-8236189 is undone/relaxed.
>> >
>> > Alex
>> >
>> > On 1/29/2020 6:44 AM, Brian Goetz wrote:
>> >>
>> >> Tagir is right, and this is yet another aspect of our technical debt
>> with regard to nesting.  Nested entities of all stripes (static vs
>> instance, class vs interface vs record vs enum) can access static members
>> from lexically enclosing contexts.
>> >>
>> >>
>> >>
>> >> On 1/29/2020 2:03 AM, Tagir Valeev wrote:
>> >>>
>> >>> But:
>> >>>
>> >>> 1. Compile time constant is not the state.
>> >>> 2. Static field of local class also cannot capture any state, even
>> >>> technically (because there's no place to store the state). Yet, this
>> code
>> >>> is allowed. I observe asymmetry here.
>> >>>
>> >>> With best regards,
>> >>> Tagir Valeev.
>> >>>
>> >>> ср, 29 янв. 2020 г., 10:39 Vicente Romero <vicente.romero at oracle.com
>:
>> >>>
>> >>>> Hi Tagir,
>> >>>>
>> >>>> This behavior is in accordance with the spec: a local record is not
a
>> >>>> local class, local records are not allowed to capture any state from
>> its
>> >>>> enclosing type. We plan to revisit this in the future not only for
>> >>>> record but as a general effort on nested-ness but for the time
being we
>> >>>> preferred to let local records immune to any capture rule that
applies
>> >>>> to local classes
>> >>>>
>> >>>> Vicente
>> >>>>
>> >>>> On 1/28/20 10:01 PM, Tagir Valeev wrote:
>> >>>>>
>> >>>>> Hello!
>> >>>>>
>> >>>>> This code is perfectly compilable (javac 14-ea+33-1439):
>> >>>>>
>> >>>>> public class RecordTest {
>> >>>>>       public static void main(String[] args) {
>> >>>>>           final int x = 2;
>> >>>>>           class X {
>> >>>>>               static final int y = x;
>> >>>>>           }
>> >>>>>       }
>> >>>>> }
>> >>>>>
>> >>>>> This is not (simply changed class to record, leaving everything
else
>> the
>> >>>>
>> >>>> same):
>> >>>>>
>> >>>>> public class RecordTest {
>> >>>>>       public static void main(String[] args) {
>> >>>>>           final int x = 2;
>> >>>>>           record X() {
>> >>>>>               static final int y = x;
>> >>>>>           }
>> >>>>>       }
>> >>>>> }
>> >>>>>
>> >>>>> Error:(5, 34) java: non-static variable x cannot be referenced
from a
>> >>>>> static context
>> >>>>>
>> >>>>> This looks counter-intuitive to me: why static field in one case
can
>> >>>>> refer to compile-time constant and in another case cannot?
>> >>>>>
>> >>>>> With best regards,
>> >>>>> Tagir Valeev
>> >>>>
>> >>
>> >
>