Where has the map method on Optional moved?

[Remi Forax]

On 02/26/2013 08:19 AM, Remi Forax wrote:
> Yes, I vote to remove it because it doesn't map :) well with the java 
> mindset.
> That said, we already discussed that and other alternatives are less 
> nice to use, at least until we use the static import trick (as with 
> reducers)

just to be crystal clear.
interface Optionalizer<T, R> {  // good name needed
   abstract R result(boolean isPresent, T element);

   public static <T> Optionalizer<T,T> orDefaultValue(T defaultValue) {
     return (isPresent, element) -> isPresent? element: defaultValue;
   }

   public static <T> Optionalizer<T, Boolean> isPresent() {
     return (isPresent, element) -> isPresent;
   }

   public static <T> Optionalizer<T, Void> andIfPresent(Consumer<? super 
T> consumer) {
     return (isPresent, element) -> {
       if (isPresent) {
         consumer.accept(element);
       }
     };
   }

   public static <T> Optionalizer<T, T> T orNull() {
     // doesn't use orDefaultValue(null) because the returned lambda is 
not constant :)
     // maybe better to do a null check in orDefaultValue
     return (isPresent, element) -> isPresent? element: null:
   }
}

with:
interface Stream<T> {
    <R> R findFirst(Optionalizer<? super T, ? extends R> optionalizer);
}

examples:
   String s = streamOfString.findFirst(orDefaultValue("<no value>")):
   boolean isPresent = streamOfString.findFirst(isPresent());
   streamOfString.findFirst(andIfPresent(System.out::println));
   String s2 = streamOfString.findFirst(orNull()):

I think i can like this.

Rémi

>
>
>
> Sent from my Phone
>
> ----- Reply message -----
> From: "Sam Pullara" <sam at sampullara.com>
> To: <lambda-libs-spec-experts at openjdk.java.net>
> Subject: Where has the map method on Optional moved?
> Date: Tue, Feb 26, 2013 06:16
>
>
> I've never been comfortable with this. I'm glad Jed is calling it out.
> Can we make Optional first class or remove it?
>
> Sam
>
> On Mon, Feb 25, 2013 at 9:12 PM, Jed Wesley-Smith <jed at wesleysmith.io> 
> wrote:
> > Hi Paul,
> >
> > You don't get a choice, it is a (or forms a) monad, you just removed
> > the useful methods (map/flatMap aka fmap/bind). This leaves clients to
> > implement them (or the functionality) in an ad-hoc and possibly buggy
> > form themselves.
> >
> > It is a monad if there exists some pair of functions:
> >
> > A -> Option<A>
> > Option<A> -> (A -> Option<B>) -> Option<B>
> >
> > The first is Optional.of, the second is currently:
> >
> > Optional<A> a = …
> > Optional<B> b = …
> > Function<A, Optional<B> f = …
> > if (a.isPresent) {
> >   b = f.apply(a.get());
> > } else {
> >   b = Optional.empty();
> > }
> >
> > rather than:
> >
> > Optional<A> a = …
> > Function<A, Optional<B> f = …
> > final Optional<B> b = a.flatMap(f);
> >
> > cheers,
> > jed.
> >
> > On 26 February 2013 00:12, Paul Sandoz <paul.sandoz at oracle.com> wrote:
> >> Hi Dhananjay,
> >>
> >> It is not missing it was removed.
> >>
> >> java.util.Optional has a narrower scope that optional things in 
> other languages. We are not trying to shoe-horn in an option monad.
> >>
> >> Paul.
> >>
> >> On Feb 23, 2013, at 12:27 AM, Dhananjay Nene 
> <dhananjay.nene at gmail.com> wrote:
> >>
> >>> It seemed to be there on the Optional class in b61 but is missing 
> now. Is
> >>> there some way to run map/flatMap operations on an Optional?
> >>>
> >>> Thanks
> >>> Dhananjay
> >>>
> >>
> >>
> >