I'm currently implementing a JNA wrapper around GTK. On GObjects we can set and get properties. These properties can be different types (Boolean, Integer, GObjects, etc). So the mapped methods look like:

g_object_set(GObject on, GPropertyByValue...property); g_object_get(GObject from, GPropertyByReference...propertyPointer);

where:

public class GPropertyByReference<T> extends GProperty<T> implements ByValue {

public String propertyName; public Pointer propertyData;

... }

public class GPropertyByValue<T> extends GProperty<T> {

public String propertyName; public T propertyData;

... }

I wanted to make GPropertyByValue and GPropertyByReference generic. I have managed it with GPropertyByReference because I can do the 'marshalling' back from the Pointer on a getValue() call as I know the type when I initially create the property (i.e. I have a contructor that takes the type). But I get stuck with GPropertyByValue.

When JNA tries to marshall this, it gets the type of the propertyData field as Object which it doesn't know what to do with.

The problem, as I see it, is that calculateSize is doing a little too much so I can't, for example, inject the type in anywhere without completely losing calculateSize. As I don't want to re-invent-the-wheel I was wondering if re-factoring the calculateSize out a little would be possible. I guess a getFieldType() method would do the trick, although I was even thinking that a seperate method for creating the structFields, which could then be overloaded, would be useful?

Other than this, is there another way to use generics in this way?

PS. I know I've called GPropertyByReference 'ByReference' when in Structure terms it's 'ByValue', but it's to indicate that the data contained within is ByReference (or Pointer).