Working with immutable collections

[Johan Haleby]

Alright that would probably work, thanks for your answer. How ever
personally I'd like to endorse immutability to a greater extent and think
it's quite an important concept that has many nice side effects. I can
imagine that it doesn't come natural for most people to use a custom
CollectionBuilder and thus working immutable data structures will feel like
a "second-class citizen" and possible neglected because it's harder and
requires extra work. By having an explicit and simple way to create an
immutable collection from a stream would probably lower the bar by quite a
margin.

Regards,
/Johan

On Mon, Nov 19, 2012 at 5:06 PM, Brian Goetz <brian.goetz at oracle.com> wrote:

> 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
>>
>>