New convenience methods on Stream

[Donald Raab]

Hi all,

I’d like to propose adding one or two of the following methods on Stream to cover more surface area of the Collections ecosystem, without requiring a big increase in the size of the Stream interface. Apologies if this has come up for discussion before. 


1. Stream contents into a mutable collection created by a Supplier. 

default <R extends Collection<T>> R toCollection(Supplier<R> supplier)
{
    return this.collect(Collectors.toCollection(supplier));
}

Usage Examples:

HashSet<String> set = stream.toCollection(HashSet::new);
TreeSet<String> sortedSet = stream.toCollection(TreeSet::new);
ArrayDeque<String> deque = stream.toCollection(ArrayDeque::new);


2. Pass the result of toArray directly into a function that can then return a Collection. This should work with Set.of, List.of and any 3rd party collections which take arrays.

default <R extends Collection<T>> R to(Function<T[], R> function)
{
    return function.apply((T[]) this.toArray());
}

Usage Examples:

Set<String> set = stream.to(Set::of);
List<String> list = stream.to(List::of);
List<String> arrayList = stream.to(Arrays::asList);


3. Stream contents directly into any mutable collection. This would then work with all other mutable JDK Collection types.

default <R extends Collection<T>> R into(R result)
{
    Collections.addAll(result, (T[]) this.toArray());
    return result;
}

Usage Examples:

HashSet<String> set = stream.into(new HashSet<>());
TreeSet<String> sortedSet = stream.into(new TreeSet<>(Comparator.reverseOrder()));
CopyOnWriteArrayList<String> list = stream.into(new CopyOnWriteArrayList<>());


There may be better default implementations, but I just wanted something here for illustrative purposes.

Thoughts?

Don