Updated State of the Lambda

[Peter Levart]

On 10/18/10, Rémi Forax wrote:
> > Why could the compiler not recognise the use of (lambda) this and
> > provide it as an argument as you suggest?
> 
> Because it's not the same object. If you mutate a method handle, you
> create a new one
> due to its immutable nature.
> 
> MethodHandle mh = #{ MethodHandle anotherMH -> mh == anotherMH };
> mh.invokeGeneric(mh) // false
> 
> because, it's translated to:
> 
> static boolean lambda$1(MethodHandle mh, MethodHandle anotherMH) {
> return mh == anotherMH;
> }
> 
> MethodHandle mh = #lambda$1;
> mh = mh.bindTo(mh);
> 
> mh.invokeGeneric(mh); // return mh == #lambda$1 => false
> 

If the identity of MethodHandle matters, another trick could be:

static boolean lambda$1(MethodHandle[] mh, MethodHandle anotherMH) {
  return mh[0] == anotherMH;
}

MethodHandle mh = #lambda$1;
MethodHandle[] temp$1 = new MethodHandle[1];
mh = mh.bindTo(temp$1);
temp$1[0] = mh;

mh.invokeGeneric(mh); // return mh == #lambda$1 => true


...for the price of another object on the heap.


Peter