On invoke dynamic and method handles

[Rémi Forax]

Iulian Dragos a écrit :
> I noticed several differences between what JSR 292
> (http://jcp.org/en/jsr/detail?id=292) says and the current
> implementation. I know this is work in progress, but at least one
> difference seems small enough to be an oversight.
>   
Currently, the first draft of the spec is outdated
and the implemntation is not up to date too.

> The signature of the bootstrap method is defined as Object(CallSite
> cs, Object... args) in code, but the JSR lists it as Object(CallSite
> cs, Object receiver, Object... args). The latter has a great
> advantage: the arguments are already prepared for a reflective call.
>   
The current idea is to implement invokedynamic like invokestatic,
i.e without a receiver.
> The contract of 'bootstrap' is that it makes the call and returns a
> value, possibly setting a target for future calls. In the current
> implementation, one would have to create a new array and strip the
> first element:
>
> cs.setTarget(mh);
> Object[] args1 = new Object[args.length - 1];
> System.arraycopy(args, 1, args1, 0, args.length - 1);
> return rm.invoke(args[0], args1);
>
> I find this to be a typical scenario, so I wonder why this deviation
> from the JSR.
>   
The spec is outdated.
> A second question: Is there a way to invoke a method handle
> generically? That means by passing an Object array, as done above
> using java.lang.reflect.Method. In other words, could method handles
> be used in the bootstrap method instead of reflect.Method?
>   
You can directly call a MethodHandle without put object in a array
by calling a invoke method with any arguments you want:
MethodHandle mh=...
mh.invoke(3,"foo");     // here 3 is not boxed

> Thanks,
> Iulia
Rémi