hg: valhalla/valhalla/langtools: Values types must be "all final".

Paul Benedict pbenedict at apache.org
Thu Jul 31 07:21:15 UTC 2014


Richard, it's off-topic but I'll say extending an enum makes no sense with
polymorphism. An enum defines the world (so to speak) of values. You then
can't allow subclasses to sneak in and change the world by introducing new
values.
On Jul 31, 2014 12:20 AM, "Richard Steiger" <rsteiger at ensemblesoft.net>
wrote:

> I'm new to this list, so may well have missed previous discussions about
> the rationale for the "Value types must be all final" pronouncement.
>
> While I'm not at all sure that value-type-finality is relevant to the
> following, I'd like to go on record stating that one of the more irritating
> aspects of the current enum semantics is the inability to extend an
> existing enum type with additional values.   I appreciate that there might
> be numerous subtleties that would need to be addressed in making enums "not
> quite final", i.e. extensible in a limited way (no overrides, etc.), the
> boon to application developers and others seems to me to justify at least
> thinking-through the issues.
>
> On 7/30/2014 8:31 PM, Paul Benedict wrote:
>
>> I've been thinking about this. When it comes to how enums were speced,
>> they
>> didn't need "final" or "class" specifiers (yes, an enum literal can be a
>> subclass but ignore that for now). So I am not sure all these explicit
>> qualifiers are helpful for writing value classes too. Granted, this is the
>> straw man implementation, but I would like to hear anyone's thoughts on
>> just making it "public value ClassName".
>> On Jul 30, 2014 5:08 PM, <paul.govereau at oracle.com> wrote:
>>
>>  Changeset: ecff516ac894
>>> Author:    pgovereau
>>> Date:      2014-07-30 17:05 -0400
>>> URL:
>>> http://hg.openjdk.java.net/valhalla/valhalla/langtools/rev/ecff516ac894
>>>
>>> Values types must be "all final".
>>>
>>> ! src/share/classes/com/sun/tools/javac/comp/TransValues.java
>>> ! src/share/classes/com/sun/tools/javac/resources/compiler.properties
>>> + test/tools/javac/diags/examples/ValueFinal.java
>>> + test/tools/javac/valhalla/values/CheckFInal.out
>>> + test/tools/javac/valhalla/values/CheckFinal.java
>>> + test/tools/javac/valhalla/values/CheckFinal.out
>>>
>>>
>>>
>


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