On Nov 15, 2007, at 2:15 PM, Duncan McGregor wrote:
Hello, I've another rococoa problem.
The return type from objc_msgSend(id theReceiver, SEL theSelector,
...) is id. This seems to be roughly equivalent to VB Variant or Java
Object, now that we have autoboxing, in that it may be a pointer to an
object, or a value. However it does seem to hold the actual value of
an int by value, rather than reference.
I've mapped this like this
public interface FoundationLibrary extends Library {
Pointer objc_msgSend(Pointer receiver, Pointer selector,
Object... args);
}
Where the return type from sending the message is NSObject all is
fine, but sometimes the value answered is, say, the int 1. In this
case I get a Pointer pointed at 0x00000001, and can't get the result
out of it (without parsing its toString or resorting to reflection).
You might make a dedicated PointerType for selector, then derive from
that based on the selector return type (PointerType->Selector-
IntSelector/FloatSelector/etc), with one selector lookup method per
return type. This captures your intent in the signature and types,
rather than exposing it as program logic when you convert Object to
something else after the method call.
Then you could do as many objc_msgSend() variants as you have return
types.
I've purposefully left out arbitrary casts between pointer and
primitive values; you can do it if you really have to but usually
it's better to make your intent explicit in the interface
definitions. If you have a function that can take either an "int" or
a "Pointer",
void func(int value);
void func(Pointer value);
is preferable to
void func(Object value);
It's a little more tricky with return values, since Java can't
overload methods which differ only by return type, so you have to
tweak the arguments to be different.
4 messages in net.java.dev.jna.usersRe: [jna-users] Returning Object type
