Record attribute binary format
Vicente Romero
vicente.romero at oracle.com
Sat Oct 12 01:36:44 UTC 2019
On 10/11/19 6:50 PM, Maurizio Cimadamore wrote:
>
> On 11/10/2019 22:19, forax at univ-mlv.fr wrote:
>> ----- Mail original -----
>>> De: "Brian Goetz" <brian.goetz at oracle.com>
>>> À: "Remi Forax" <forax at univ-mlv.fr>, "amber-spec-experts"
>>> <amber-spec-experts at openjdk.java.net>
>>> Envoyé: Vendredi 11 Octobre 2019 22:57:23
>>> Objet: Re: Record attribute binary format
>>> No need. Varargs-ness is reified with the (mandated) canonical ctor.
>> hum, this looks like a hack, it means you can not just read the
>> Record attribute, you have to crawle all the methods to find the
>> primary constructor.
>
> It _looks_ like an hack, but I think that, after some more thinking
> it's actually more correct than what you are proposing. A record
> contains a bunch of components, the components have a name and a type.
> Vararg-ness is immaterial here; both
>
> record Foo(Object[] arr) { ... }
>
> and
>
> record Bar(Object... arr) { ... }
>
> Denote the same underlying state (e.g. an Object array). The only
> difference between Foo and Bar is that their _construction protocol_
> is different (which might also mean, in the future, that Bar will get
> more liberal _deconstruction_ protocols too!); but this is cleanly
> captured in the canonical constructor method_info.
>
> Pedagolical test: would an 'isVarargs()' predicate on the core
> reflection record component be acceptable?
that method as already added to j.l.r.RecordComponent, see [1],
> Ugh, I don't think so. Varargs is a method concept; record components
> are a bit ephemeral, yes, but they are definitively _not_ methods.
>
> Maurizio
Vicente
[1]
http://hg.openjdk.java.net/amber/amber/file/df5e1c317777/src/java.base/share/classes/java/lang/reflect/RecordComponent.java#l209
>
>
>>
>> and if we take a look to the past, we have added access flags to
>> methods, fields and classes, so there is a non negligible chance that
>> we will want to do the same to record components in the future.
>>
>> Rémi
>>
>>> On 10/11/2019 4:43 PM, Remi Forax wrote:
>>>> It seems we have to add an access_flag for each record component
>>>> because we have
>>>> to mark if the record component is a varargs or not.
>>>>
>>>> So the format should be
>>>>
>>>> Record_attribute {
>>>> u2 attribute_name_index;
>>>> u4 attribute_length;
>>>> u2 number_of_record_components;
>>>> { u2 component_access_flags;
>>>> u2 component_name_index;
>>>> u2 component_descriptor_index;
>>>> u2 attribute_count;
>>>> attribute_info attributes[attributes_count];
>>>> }
>>>> }
>>>>
>>>> with the component_access_flags allowing ACC_VARARGS.
>>>>
>>>> Rémi
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