Question about MapStream.intoMulti

[Brian Goetz]

This one is a leftover from when we had a separate stream shape for multimap.   Now you can simulate this with 

mapStream.mapValues(v -> singletonList(v))

Sent from my iPhone

On May 5, 2012, at 6:02 AM, François Sarradin <fsarradin at gmail.com> wrote:

> Hi all,
> 
> I would like to know what is the purpose of the method MapStream.intoMulti?
> Is it convert a MapStream into a Map of Collection[s] ?
> 
> Here is an example that I have tried with this method:
> 
>    public static Map<DevelopmentStage, Collection<Person>>
> distribute(Iterable<Person> persons) {
>        return persons
>                     .groupBy(Age::getDevelopmentStage)
>                     .intoMulti(
>                         new HashMap<DevelopmentStage,
> Collection<Person>>(),
>                         () -> new ArrayList<Person>());
>    }
> 
> But this code generates this error:
> 
> error: method intoMulti in interface MapStream<K,V> cannot be applied to
> given types;
> required: A,Factory<C>
> found: HashMap<DevelopmentStage,Collection<Person>>,lambda
> reason: invalid inferred types for A,C
> reason: inferred type does not conform to declared bound(s)
> inferred: HashMap<DevelopmentStage,Collection<Person>>
> bound(s): Map<? super DevelopmentStage,ArrayList<Person>>
> where A,C,V,K are type-variables:
> A extends Map<? super DevelopmentStage,C> declared in method
> <A,C>intoMulti(A,Factory<C>)
> C extends Collection<? super V> declared in method
> <A,C>intoMulti(A,Factory<C>)
> V extends Object declared in interface MapStream
> K extends Object declared in interface MapStream
> 
> Am I wrong ? Why the lambda expression is not inferred into
> Factory<Collection<Person>> ?
> 
> Thanks,
> 
> Francois Sarradin
>