RFR: 8072727 - add variation of Stream.iterate() that's finite

[Paul Sandoz]

Hi Tagir,

> On 21 Feb 2016, at 13:15, Tagir Valeev <amaembo at gmail.com> wrote:
> 
> Thank you for valueable coments, here's updated webrev:
> 
> http://cr.openjdk.java.net/~tvaleev/webrev/8072727/r2/
> 
> Changes:
> - Spec updated according to Brian Goetz suggestion
> - Predicate<? super T> wildcard
> - two-arg versions of iterate() are rewritten with Spliterator and started flag
> - IterateTest rewritten: now withData().stream().expectedResult().exercize() used; expected results added.
> 

Looking good. Just minor comments.

For the primitive streams
—

+        Spliterator.OfDouble spliterator = new Spliterators.AbstractDoubleSpliterator(Long.MAX_VALUE,
+               Spliterator.ORDERED | Spliterator.IMMUTABLE) {
+            double prev;
...
-        return StreamSupport.doubleStream(Spliterators.spliteratorUnknownSize(
-                iterator,
-                Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL), false);

We should retain the NONNULL characteristic.

Thinking a little more that is something that should perhaps be added by default by the primitive abstract spliterators. Something to consider later maybe.


Stream
—

     public static<T> Stream<T> iterate(final T seed, final UnaryOperator<T> f) {
         Objects.requireNonNull(f);

-        final Iterator<T> iterator = new Iterator<T>() {
-            @SuppressWarnings("unchecked")
-            T t = (T) Streams.NONE;

I believe you can now remove the field Streams.NONE?


1186     public static<T> Stream<T> iterate(final T seed, final UnaryOperator<T> f) {
1187         Objects.requireNonNull(f);
1188         Spliterator<T> spliterator = new Spliterators.AbstractSpliterator<T>(Long.MAX_VALUE,
1189                Spliterator.ORDERED | Spliterator.IMMUTABLE) {

I forgot to mention before you can now use the “<>" on the RHS, although IDEs might not like it javac will :-)


1270             @Override
1271             public void forEachRemaining(Consumer<? super T> action) {
1272                 Objects.requireNonNull(action);
1273                 if (finished)
1274                     return;
1275                 T t = started ? f.apply(prev) : seed;
1276                 finished = true;

A really minor thing but if you move “finished = true” above one line, it means there is one less place where unintended recursive traversal can occur.


IterateTest
—

  57             {Arrays.asList(1, 2, 4, 8, 16, 32, 64, 128, 256, 512),
  58                 Factory.ofSupplier("ref.ten", () -> Stream.iterate(1, x -> x < 1000, x -> x * 2))},

We now have the method “List.of", up to you if you wanna update to use that or not.


Thanks,
Paul.