[Bug]: unexpected data type for `List` fields in OPM

[JoelGaechter]

What happened?

When trying to query multiple values as a collection using a single tag, as follows, the (inner) datatypes returned do not match the field.

@PlcTag("input-register:1:UINT[2]")
private List<Integer> registers;

The field on the returned (ByteBuddy proxy) instance would be of type List<PlcUINT>. The problem is that if we then want to use list elements as Integer, this causes a ClassCastException.

The expected behavior IMO would be that the list is of type List<Integer> similar as it works for single values, e.g, @PlcTag("input-register:1:UINT") => int.

Note:
When trying to use an array, e.g., int[] instead, the field can not be assigned at all, as the call returns a list.

Version

v0.12.0

Programming Languages

• plc4j
• plc4go
• plc4c
• plc4net

Protocols

• AB-Ethernet
• ADS /AMS
• BACnet/IP
• CANopen
• DeltaV
• DF1
• EtherNet/IP
• Firmata
• KNXnet/IP
• Modbus
• OPC-UA
• S7

[JoelGaechter]

As off right now, these fields are se using the fallback behavior of PlcEntityInterceptor::getTyped:

Object responseObject = response.getObject(sourceFieldName);
if (clazz.isAssignableFrom(responseObject.getClass())) {
    return responseObject;
}

The preferrable option would be to call the respective PlcReadResponse::getAll... instead of PlcReadResponse::getObject if the field type is a collection (or array). For this, the generic type might need to be determined though. While for arrays, this can be done using Class::getComponentType, for collections TypeToken might be the way to go. Additionally, if specific collection types should be supported, further processing might be required as PlcReadResponse::getAll... returns a generic Collection.