Array of booleans

[forax at univ-mlv.fr]

> De: "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>
> À: "Remi Forax" <forax at univ-mlv.fr>, "panama-dev at openjdk.java.net'"
> <panama-dev at openjdk.java.net>
> Envoyé: Jeudi 18 Mars 2021 16:09:01
> Objet: Re: Array of booleans

> On 18/03/2021 15:04, Remi Forax wrote:

>> Hi everybody,
>> It seems it's not possible to create a VarHandle on array of booleans
>>  static final VarHandle BOOLEAN_HANDLE = ofSequence(ofValueBits(8,
>>   LITTLE_ENDIAN))
>>         .varHandle(boolean.class, sequenceElement());

>> Is there a reason for that ?

>> From the JVM POV, a boolean is stores on 8 bits and in the bytecode
>> baload/bastore can load/store from either an array of booleans or an array of
>> bytes.

> If I'm not mistaken, that representation is not specfied? E.g. hotspot uses it,
> but there is latitude? Quoting from VM spec:

> ```

> In Oracle’s Java Virtual Machine implementation, boolean arrays in the Java
> programming language are encoded as Java Virtual Machine byte arrays, using 8
> bits per boolean element.
> ```

> Note "Oracle" :-)

> That was the rationale for omitting booleans. It should be possible to use
> custom adapters if you want to speculate on the shape of e.g. a boolean array -
> but we'd prefer not to add VM impl-specific assumption - or that was the idea
> at least.
It works with JNI, boolean is mapped into an unsigned 8 bits 
https://docs.oracle.com/en/java/javase/16/docs/specs/jni/types.html 

> Maurizio
Rémi