CompletableFuture

[Doug Lea]

On 11/28/12 11:09, Remi Forax wrote:

>> The void completion methods don't return new CompletableFuture (no need)
>> but just "return this" to be nice to fluency fans.
>
> aaaaaah,
> It means that with
>    CompletableFuture<T> c = completableFuture.then(e -> foo(e));
> c.isDone() can be true even if foo() has still not finished.
>
> Having a fluent interface is a nice trick but here, the resulting semantics is
> too weird IMO.
>

Thanks. Good point. I initially defined these as void (as opposed to
the Function ones, that return a new one to maintain value). Changing
to "return this" makes them much simpler to use but as you point
out makes it look like the "." in a compound expression refers
to the wrong thing. I guess the best way out is to
actually create/return a little CompletableFuture<Void> here,
which doesn't appreciably inflate cost and precludes misinterpretation.
So...

    /**
      * Creates and returns a CompletableFuture> that is completed
      * after performing the given action with the result of this
      * CompletableFuture if/when it completes normally.
      *
      * @return the new CompletableFuture
      */
     public CompletableFuture<Void> then(Block<? super T> action);


And similarly for and(), or(), exceptionally().
We still have the function vs action method overriding issue though.

-Doug