From Function<T, Boolean> to t Predicate<T> - What is preferred ?

[Brian Goetz]

There is a lot of flexibility permitted when adapting method references 
to functional interfaces, for this very reason.  So Iters::beginsWithA 
should easily convert to either a Predicate<String> or a 
Function<String, Boolean>.

Capturing a stateless lambda (static method reference, unbound instance 
method reference, or lambda that captures nothing from the environment) 
is basically free.  Capturing a bound method reference or stateful 
lambda is (currently) exactly as costly as creating an inner class 
instance.

In the future, we may well be able to optimize these capture costs; we 
have a lot of plans on the drawing board, but the implementation 
strategy for 8 has already converged.  So for the time being, capturing 
map::apply is an object creation, whereas capturing Iters::beginWithA is 
not.

On 12/31/2012 1:50 PM, Boaz Nahum wrote:
> So Predicate<T> is not Function<T, Boolean>
>
> class Iters {
>
>      static boolean beginWithA(String s) {
>          return s.startsWith("a");
>      }
> }
>
> Function<String, Boolean> map = Iters::beginWithA;
>
> Should we
>
>            Predicate<String> filter = Iters::beginWithA;
>
> Or this is not too bad:
> Predicate<String> filter = map::apply
>
> Will optimization come to rescue us in the second case
>
> Thanks
> Boaz
>