Strict long type casting

[Ty Young]

On 4/6/20 8:12 PM, Maurizio Cimadamore wrote:
> Hi Ty,
> I'd need to have a look at the code of MemoryNumber/MemoryLong to 
> understand what's going on.


The abstract class can be found here:


https://github.com/BlueGoliath/Crosspoint/blob/master/src/main/java/org/goliath/crosspoint/abstracts/NativeNumber.java


implementation:


https://github.com/BlueGoliath/Crosspoint/blob/master/src/main/java/org/goliath/crosspoint/numbers/NativeLong.java


(classes have just been renamed. Same code)


Basic usage:


NativeLong test = new NativeLong();

test.setValue(Long.MAX_VALUE);

System.out.println(test.byteValue());


Which fails with:


Caused by: java.lang.invoke.WrongMethodTypeException: cannot convert 
MethodHandle(VarHandle,MemoryAddress)long to (VarHandle,MemoryAddress)int
     at 
java.base/java.lang.invoke.MethodHandle.asTypeUncached(MethodHandle.java:881)
     at 
java.base/java.lang.invoke.MethodHandle.asType(MethodHandle.java:866)
     at 
java.base/java.lang.invoke.VarHandleGuards.guard_L_I(VarHandleGuards.java:106)
     at 
org.goliath.crosspoint/org.goliath.crosspoint.abstracts.NativeNumber.intValue(NativeNumber.java:46)
     at java.base/java.lang.Number.byteValue(Number.java:104)


...but only with long.



>
> Thanks
> Maurizio
>
> On 07/04/2020 01:49, Ty Young wrote:
>> Hi all,
>>
>>
>> I'm trying to create a way of reading primitive number based struct 
>> values(since VarHandle.get is polymorphic) by combining Java's Number 
>> abstract class with my abstraction like so:
>>
>>
>> public abstract class MemoryNumber<E extends Number> extends Number 
>> implements MemoryValue<E>
>>
>>
>> Which is then extended by classes like "MemoryLong".
>>
>>
>> The problem here is that with long(and only long) the type casting is 
>> strict and fails. Attempting to call byteValue() fails on intValue(). 
>> This doesn't, for whatever reason, happen with normal on-heap long 
>> values nor does it happen with an MemoryInt implementation either.
>>
>>
>> I tried looking in the source code of Long.class and I couldn't find 
>> anything that I was doing differently besides using Panama, so I'm a 
>> bit lost here. Does anyone know what's going on?
>>