Into

[Brian Goetz]

> I was just translating a simple example from Uncle Bob's recent FP
> resolution(*).  The most difficult problem given the current state of
> jkd8lambda was trying to print a stream...
>
> Using StringJoiner seems like the coolest way to do this currently:
>
>    stream.into(new StringJoiner(", ", "[", "]"))

Right, that's the current plan.  StringJoiner implements 
Stream.Destination.

> But how's this supposed to work without into()?

Well, that's one of the things to figure out.  I think it fits pretty 
nicely as a mutable reduce.

   make-accumulator() -> new StringJoiner()
   accumulate(a, e) -> a.add(e)
   combine(a1, a2) -> if (!a2.isEmpty) a1.addAll(a2)

This parallelizes well.  The only trickiness is adding the pre/post 
strings, which have to be deferred to the very end.  All doable.

> Btw, the lack of a generic Joiner that accepts any ol' object or
> primitive is causing me some grief.  Given a stream of ints or even
> Integers, having to manually map(Object::toString) seems like something
> StringJoiner should be doing automatically.

Yeah, it should accept Object and call toString on it. 
String.toString() is cheap.