Updated State of the Lambda

[Peter Levart]

On 10/18/10, Rémi Forax wrote:
>   Le 18/10/2010 16:14, Maurizio Cimadamore a écrit :
> > On 18/10/10 15:05, Peter Levart wrote:
> >> 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.
> >>>
> >>>
> >> Ah, now I understand your concern. You would like lambda expressions to be convertible to method handles (java.dyn.MethodHandle) as well as to SAM types.
> >>
> >>
> >>> 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
> >>>
> >> Why couldn't compiler translate it to:
> >>
> >> static boolean lambda$1(MethodHandle anotherMH) {
> >>     return #lambda$1 == anotherMH;
> >> }
> >>
> >> MethodHandle mh = #lambda$1;
> >>
> >> mh.invokeGeneric(mh); // return #lambda$1 == #lambda$1 =>   true?
> >>
> > Hi Peter,
> > note that the bindTo/insertArgs solution avoids the problem that one or
> > more 'synthetic' arguments could not be available anymore when the
> > lambda expression is called (i.e. when the Sam type escapes its creation
> > context). You really want clients to just specify the arguments required
> > by the SAM method, regardless of any other synthetic arg that the
> > compiler might have inserted in the translated code.
> >
> > Maurizio
> 
> As Maurizio said, it doesn't work if the lambda capture variable 
> contents from outer scope.

Why not. Example:

final String s = "abc";
final MethodHandle mh = #{ String str -> str.startsWith(s) || !str.isEmpty() && mh.invokeGeneric(str.substring(1)) };

Could be translated to:

static boolean lambda$2(String _s, String str) {
  MethodHandle _mh = (#lambda$2).bindTo(_s);
  return str.startsWith(_s) || !str.isEmpty() && _mh.invokeGeneric(str.substring(1));
}
...
final String s = "abc";
final MethodHandle mh = (#lambda$2).bindTo(s);


Peter

> 
> >> Peter
> 
> Rémi
> 
>