Record attribute binary format

[Vicente Romero]

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