Where has the map method on Optional moved?

[Paul Sandoz]

Hi Jed,

An Optional.flatMap is somewhat different to Stream.flatMap(FlatMapper ). Should we also add filter, forEach and reduce methods to have some parity to that of Stream? that is what i am getting at when i used the expression "shoe-horn".

Stream.flatMap has been through a number of renames/redesigns and has very recently somewhat circled back on itself *and* we have added the following convenience method to Stream<T>:

    default <R> Stream<R> flatMap(Function<T, Stream<? extends R>> mapper) {
        return flatMap((T t, Consumer<R> sink) -> mapper.apply(t).sequential().forEach(sink));
    }

Since we are using the "flatMap" name it was felt important to have one method follow the pattern expected of it.

Hmm... maybe under such circumstances it is OK to add an Optional.flatMap ? Or alternatively choose a completely different name to disassociate from Stream e.g. like Guava's Optional.transform.

Paul.

On Feb 26, 2013, at 6:12 AM, 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
>>> 
>> 
>>