incompatible types compile error

[Henry Jen]

On Nov 19, 2012, at 10:10 PM, Ricky Clarkson <ricky.clarkson at gmail.com> wrote:

> From the original post:
> 
>  .sorted(comparing((Mapper<Comparable, Album>) album ->
> 
> Note the raw Comparable.
> 

Yes, but I assume that was at the point where Mapper have the type declaration of Mapper<To, From>, in that case, Comparators.comparing should still return Comparator<Album>. I must miss some point.

Cheers,
Henry


> 
> On Tue, Nov 20, 2012 at 2:55 AM, Henry Jen <henry.jen at oracle.com> wrote:
> On 11/19/2012 05:37 AM, Maurizio Cimadamore wrote:
> > The problem is that, since you are using Comparable (note the absence of
> > type-parameters) you are effectively triggering an uunchecked conversion
> > there - the result would be that the erased signature of 'into' will be
> > used instead - that is, the return type of into will be simply
> > Destination - not the type inferred from the argument - hence the
> > incompatible types error.
> >
> 
> I don't quite understand this Comparable cause erased signature for into.
> 
> Comparators.comparing<Function<Album, ? extends Comparable>> should
> return a Comparator<Album> given correct Function type, then in
> sorted(Comparator<Album>) should gave a Stream<Album>, isn't the type
> obvious?
> 
> Apology if this is a dumb question, I don't know how exactly type
> inference works. But seems to me, the target type is available. What am
> I missing? Thanks in advance.
> 
> Cheers,
> Henry
> 
> 
> > Btw - I'm getting the error for both versions of the example you sent.
> >
> > Maurizio
> >
> > On 16/11/12 23:01, Arul Dhesiaseelan wrote:
> >> This works, btw.
> >>
> >> List<Album> sortedFavs = new ArrayList<Album>();
> >> albums.stream()
> >>              .filter(a -> a.tracks.stream().anyMatch(t -> (t.rating >= 4)))
> >>              .sorted(comparing((Mapper<Comparable, Album>) album ->
> >> album.name))
> >>              .into(sortedFavs);
> >>
> >>
> >>
> >> On Fri, Nov 16, 2012 at 12:38 PM, Remi Forax <forax at univ-mlv.fr> wrote:
> >>
> >>> On 11/16/2012 10:57 PM, Arul Dhesiaseelan wrote:
> >>>> Hi,
> >>>>
> >>>> I am trying to run a slightly modified version from the latest State of
> >>> the
> >>>> Lambda libraries edition.
> >>>>
> >>>>       List<Album> sortedFavs =
> >>>>           albums.stream()
> >>>>               .filter(a -> a.tracks.stream().anyMatch(t -> (t.rating >=
> >>> 4)))
> >>>>               .sorted(comparing((Mapper<Comparable, Album>) album ->
> >>>> album.name))
> >>>>               .into(new ArrayList<Album>());
> >>>>
> >>>> java: incompatible types: java.util.stream.Stream.Destination cannot be
> >>>> converted to java.util.List<Album>
> >>>>
> >>>> Any idea what could be wrong here?
> >>> the signature of the method into.
> >>>
> >>>> -Arul
> >>>>
> >>> Rémi
> >>>
> >>>
> >>>
> >
> >
> 
> 
>