Working with immutable collections

[Brian Goetz]

I understand the use case.

The specific suggestion (add a new stream operation for this one use 
case, that cannot help with others, and will invariably give birth to 
cries for many more) would be a serious mistake.

What I think you want is a Builder that implements Destination, 
therefore piggybacking on the mechanism that lets into work with any 
Collection type (and more).  Then it is entirely supported within the 
library:

   class MyCollectionBuilder<T> implements Stream.Destination {
     void addAll(...)

     T build() ...
   }

and then you could say

   stream.filter(...).blah(...)
         .into(new MyCollectionBuilder(new ArrayList())).build();



On 11/19/2012 9:39 AM, Johan Haleby wrote:
> Hi,
>
> I'm sorry if this has been discussed before but here goes:
>
> Let's say I have an immutable list called "xList" that I want to filter and
> return the result as a new *immutable* list. I could do something like this:
>
> Collections.unmodifiableList(xList.filter(obj -> obj.something()).into(new
> ArrayList<X>())));
>
> How ever I think this is quite verbose and doesn't follow the fluent style
> of the API. What I would like to have is something a long these lines:
>
> xList.filter(obj -> obj.something()).intoImmutable(new ArrayList<X>()));
>
> "intoImmutable" could then do "Collections.unmodifiableList(..)" for me so
> I don't need to wrap all statements where I want to return an immutable
> collection.
>
> What are your thoughts on this?
>
> Regards,
> /Johan
>