Additional Collectors

[Tim Peierls]

On Wed, Apr 3, 2013 at 1:27 PM, Brian Goetz <brian.goetz at oracle.com> wrote:

> People also expressed concern that the "toMap()" (nee mappedTo,
> joiningWith) is not flexible enough.  As a reminder, what toMap does is
> take a Stream<T> and a function T->U and produces a Map<T,U>.  Some people
> call this "backwards"; they would rather have something that takes a
> Stream<T> and function T->K and produces a Map<K,T>.  And others would
> rather have something that takes two functions T->K and T->U and produces a
> Map<K,U>.
>

The second form (Stream<T> and T->K producing Map<K, T>) could be called
"indexing", so toIndexMap or toIndex would seem appropriate. I don't have a
sense of a natural name for the third form. toMap still seems good for the
first form.



> All of these are useful enough.  The question is how to fit them into the
> API.  I think the name "toMap" is a bit of a challenge, since there are
> several "modes" and not all of them can be easily handled by overloads.
>  Maybe:
>
>   toMap(T->U) // first version
>   toMap(T->K, T->U) // third version
>
> and leave the second version out, since the third version can easily
> simulate the second?
>

Maybe, but I like the thought of toIndex or something like that.

--tim