Java Code Examples for java.util.Spliterator#trySplit()

The following examples show how to use java.util.Spliterator#trySplit() . You can vote up the ones you like or vote down the ones you don't like, and go to the original project or source file by following the links above each example. You may check out the related API usage on the sidebar.

Example 1

Source File: SpliteratorCollisions.java From openjdk-jdk8u-backup with GNU General Public License v2.0

6 votes

private static <T, S extends Spliterator<T>> void testSplitAfterFullTraversal(
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter) {
    // Full traversal using tryAdvance
    Spliterator<T> spliterator = supplier.get();
    while (spliterator.tryAdvance(boxingAdapter.apply(e -> { }))) { }
    Spliterator<T> split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using forEach
    spliterator = supplier.get();
    spliterator.forEachRemaining(boxingAdapter.apply(e -> {
    }));
    split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using tryAdvance then forEach
    spliterator = supplier.get();
    spliterator.tryAdvance(boxingAdapter.apply(e -> { }));
    spliterator.forEachRemaining(boxingAdapter.apply(e -> {
    }));
    split = spliterator.trySplit();
    assertNull(split);
}

Example 2

Source File: SpliteratorTraversingAndSplittingTest.java From jdk8u60 with GNU General Public License v2.0

6 votes

private static <T, S extends Spliterator<T>> void testSplitOnce(
        Collection<T> exp,
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter) {
    S spliterator = supplier.get();
    long sizeIfKnown = spliterator.getExactSizeIfKnown();
    boolean isOrdered = spliterator.hasCharacteristics(Spliterator.ORDERED);

    ArrayList<T> fromSplit = new ArrayList<>();
    Spliterator<T> s1 = supplier.get();
    Spliterator<T> s2 = s1.trySplit();
    long s1Size = s1.getExactSizeIfKnown();
    long s2Size = (s2 != null) ? s2.getExactSizeIfKnown() : 0;
    Consumer<T> addToFromSplit = boxingAdapter.apply(fromSplit::add);
    if (s2 != null)
        s2.forEachRemaining(addToFromSplit);
    s1.forEachRemaining(addToFromSplit);

    if (sizeIfKnown >= 0) {
        assertEquals(sizeIfKnown, fromSplit.size());
        if (s1Size >= 0 && s2Size >= 0)
            assertEquals(sizeIfKnown, s1Size + s2Size);
    }
    assertContents(fromSplit, exp, isOrdered);
}

Example 3

Source File: SpliteratorTestHelper.java From jdk8u60 with GNU General Public License v2.0

6 votes

private static <T, S extends Spliterator<T>> void testSplitAfterFullTraversal(
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter) {
    // Full traversal using tryAdvance
    Spliterator<T> spliterator = supplier.get();
    while (spliterator.tryAdvance(boxingAdapter.apply(e -> { }))) { }
    Spliterator<T> split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using forEach
    spliterator = supplier.get();
    spliterator.forEachRemaining(boxingAdapter.apply(e -> { }));
    split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using tryAdvance then forEach
    spliterator = supplier.get();
    spliterator.tryAdvance(boxingAdapter.apply(e -> { }));
    spliterator.forEachRemaining(boxingAdapter.apply(e -> { }));
    split = spliterator.trySplit();
    assertNull(split);
}

Example 4

Source File: SpliteratorTestHelper.java From TencentKona-8 with GNU General Public License v2.0

6 votes

static<U> void mixedTraverseAndSplit(Consumer<U> b, Spliterator<U> splTop) {
    Spliterator<U> spl1, spl2, spl3;
    splTop.tryAdvance(b);
    spl2 = splTop.trySplit();
    if (spl2 != null) {
        spl2.tryAdvance(b);
        spl1 = spl2.trySplit();
        if (spl1 != null) {
            spl1.tryAdvance(b);
            spl1.forEachRemaining(b);
        }
        spl2.tryAdvance(b);
        spl2.forEachRemaining(b);
    }
    splTop.tryAdvance(b);
    spl3 = splTop.trySplit();
    if (spl3 != null) {
        spl3.tryAdvance(b);
        spl3.forEachRemaining(b);
    }
    splTop.tryAdvance(b);
    splTop.forEachRemaining(b);
}

Example 5

Source File: SpliteratorTraversingAndSplittingTest.java From jdk8u-jdk with GNU General Public License v2.0

6 votes

private static <T, S extends Spliterator<T>> void testSplitAfterFullTraversal(
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter) {
    // Full traversal using tryAdvance
    Spliterator<T> spliterator = supplier.get();
    while (spliterator.tryAdvance(boxingAdapter.apply(e -> { }))) { }
    Spliterator<T> split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using forEach
    spliterator = supplier.get();
    spliterator.forEachRemaining(boxingAdapter.apply(e -> {
    }));
    split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using tryAdvance then forEach
    spliterator = supplier.get();
    spliterator.tryAdvance(boxingAdapter.apply(e -> { }));
    spliterator.forEachRemaining(boxingAdapter.apply(e -> {
    }));
    split = spliterator.trySplit();
    assertNull(split);
}

Example 6

Source File: SpliteratorCollisions.java From dragonwell8_jdk with GNU General Public License v2.0

6 votes

private static <T, S extends Spliterator<T>> void testSplitAfterFullTraversal(
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter) {
    // Full traversal using tryAdvance
    Spliterator<T> spliterator = supplier.get();
    while (spliterator.tryAdvance(boxingAdapter.apply(e -> { }))) { }
    Spliterator<T> split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using forEach
    spliterator = supplier.get();
    spliterator.forEachRemaining(boxingAdapter.apply(e -> {
    }));
    split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using tryAdvance then forEach
    spliterator = supplier.get();
    spliterator.tryAdvance(boxingAdapter.apply(e -> { }));
    spliterator.forEachRemaining(boxingAdapter.apply(e -> {
    }));
    split = spliterator.trySplit();
    assertNull(split);
}

Example 7

Source File: SpliteratorTraversingAndSplittingTest.java From openjdk-jdk8u with GNU General Public License v2.0

6 votes

private static <T, S extends Spliterator<T>> void testSplitAfterFullTraversal(
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter) {
    // Full traversal using tryAdvance
    Spliterator<T> spliterator = supplier.get();
    while (spliterator.tryAdvance(boxingAdapter.apply(e -> { }))) { }
    Spliterator<T> split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using forEach
    spliterator = supplier.get();
    spliterator.forEachRemaining(boxingAdapter.apply(e -> {
    }));
    split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using tryAdvance then forEach
    spliterator = supplier.get();
    spliterator.tryAdvance(boxingAdapter.apply(e -> { }));
    spliterator.forEachRemaining(boxingAdapter.apply(e -> {
    }));
    split = spliterator.trySplit();
    assertNull(split);
}

Example 8

Source File: SpliteratorTestHelper.java From TencentKona-8 with GNU General Public License v2.0

6 votes

private static <T, S extends Spliterator<T>> void testSplitAfterFullTraversal(
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter) {
    // Full traversal using tryAdvance
    Spliterator<T> spliterator = supplier.get();
    while (spliterator.tryAdvance(boxingAdapter.apply(e -> { }))) { }
    Spliterator<T> split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using forEach
    spliterator = supplier.get();
    spliterator.forEachRemaining(boxingAdapter.apply(e -> { }));
    split = spliterator.trySplit();
    assertNull(split);

    // Full traversal using tryAdvance then forEach
    spliterator = supplier.get();
    spliterator.tryAdvance(boxingAdapter.apply(e -> { }));
    spliterator.forEachRemaining(boxingAdapter.apply(e -> { }));
    split = spliterator.trySplit();
    assertNull(split);
}

Example 9

Source File: SpliteratorTraversingAndSplittingTest.java From dragonwell8_jdk with GNU General Public License v2.0

6 votes

private static <T, S extends Spliterator<T>> void testSplitOnce(
        Collection<T> exp,
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter) {
    S spliterator = supplier.get();
    long sizeIfKnown = spliterator.getExactSizeIfKnown();
    boolean isOrdered = spliterator.hasCharacteristics(Spliterator.ORDERED);

    ArrayList<T> fromSplit = new ArrayList<>();
    Spliterator<T> s1 = supplier.get();
    Spliterator<T> s2 = s1.trySplit();
    long s1Size = s1.getExactSizeIfKnown();
    long s2Size = (s2 != null) ? s2.getExactSizeIfKnown() : 0;
    Consumer<T> addToFromSplit = boxingAdapter.apply(fromSplit::add);
    if (s2 != null)
        s2.forEachRemaining(addToFromSplit);
    s1.forEachRemaining(addToFromSplit);

    if (sizeIfKnown >= 0) {
        assertEquals(sizeIfKnown, fromSplit.size());
        if (s1Size >= 0 && s2Size >= 0)
            assertEquals(sizeIfKnown, s1Size + s2Size);
    }
    assertContents(fromSplit, exp, isOrdered);
}

Example 10

Source File: SpliteratorTestHelper.java From openjdk-jdk8u with GNU General Public License v2.0

6 votes

static<U> void mixedTraverseAndSplit(Consumer<U> b, Spliterator<U> splTop) {
    Spliterator<U> spl1, spl2, spl3;
    splTop.tryAdvance(b);
    spl2 = splTop.trySplit();
    if (spl2 != null) {
        spl2.tryAdvance(b);
        spl1 = spl2.trySplit();
        if (spl1 != null) {
            spl1.tryAdvance(b);
            spl1.forEachRemaining(b);
        }
        spl2.tryAdvance(b);
        spl2.forEachRemaining(b);
    }
    splTop.tryAdvance(b);
    spl3 = splTop.trySplit();
    if (spl3 != null) {
        spl3.tryAdvance(b);
        spl3.forEachRemaining(b);
    }
    splTop.tryAdvance(b);
    splTop.forEachRemaining(b);
}

Example 11

Source File: UnmodifiableMapEntrySet.java From jdk8u60 with GNU General Public License v2.0

5 votes

void testSpliterator(Supplier<Spliterator<Map.Entry<Integer, Integer>>> ss,
                     // Higher order function that given a spliterator returns a
                     // consumer for that spliterator which traverses elements
                     // using an EntryConsumer
                     Function<Spliterator<Map.Entry<Integer, Integer>>, Consumer<EntryConsumer>> sc) {
    testWithEntryConsumer(sc.apply(ss.get()));

    Spliterator<Map.Entry<Integer, Integer>> s = ss.get();
    Spliterator<Map.Entry<Integer, Integer>> split = s.trySplit();
    if (split != null) {
        testWithEntryConsumer(sc.apply(split));
        testWithEntryConsumer(sc.apply(s));
    }
}

Example 12

Source File: SpliteratorTestHelper.java From openjdk-jdk8u-backup with GNU General Public License v2.0

5 votes

private static <T, S extends Spliterator<T>> void testSplitOnce(
        Collection<T> exp,
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter,
        ContentAsserter<T> asserter) {
    S spliterator = supplier.get();
    long sizeIfKnown = spliterator.getExactSizeIfKnown();
    boolean isOrdered = spliterator.hasCharacteristics(Spliterator.ORDERED);

    ArrayList<T> fromSplit = new ArrayList<>();
    Spliterator<T> s1 = supplier.get();
    Spliterator<T> s2 = s1.trySplit();
    long s1Size = s1.getExactSizeIfKnown();
    long s2Size = (s2 != null) ? s2.getExactSizeIfKnown() : 0;
    Consumer<T> addToFromSplit = boxingAdapter.apply(fromSplit::add);
    if (s2 != null)
        s2.forEachRemaining(addToFromSplit);
    s1.forEachRemaining(addToFromSplit);

    if (sizeIfKnown >= 0) {
        assertEquals(sizeIfKnown, fromSplit.size());
        if (s1Size >= 0 && s2Size >= 0)
            assertEquals(sizeIfKnown, s1Size + s2Size);
    }

    asserter.assertContents(fromSplit, exp, isOrdered);
}

Example 13

Source File: UnmodifiableMapEntrySet.java From openjdk-jdk8u with GNU General Public License v2.0

5 votes

void testSpliterator(Supplier<Spliterator<Map.Entry<Integer, Integer>>> ss,
                     // Higher order function that given a spliterator returns a
                     // consumer for that spliterator which traverses elements
                     // using an EntryConsumer
                     Function<Spliterator<Map.Entry<Integer, Integer>>, Consumer<EntryConsumer>> sc) {
    testWithEntryConsumer(sc.apply(ss.get()));

    Spliterator<Map.Entry<Integer, Integer>> s = ss.get();
    Spliterator<Map.Entry<Integer, Integer>> split = s.trySplit();
    if (split != null) {
        testWithEntryConsumer(sc.apply(split));
        testWithEntryConsumer(sc.apply(s));
    }
}

Example 14

Source File: UnmodifiableMapEntrySet.java From jdk8u-jdk with GNU General Public License v2.0

5 votes

void testSpliterator(Supplier<Spliterator<Map.Entry<Integer, Integer>>> ss,
                     // Higher order function that given a spliterator returns a
                     // consumer for that spliterator which traverses elements
                     // using an EntryConsumer
                     Function<Spliterator<Map.Entry<Integer, Integer>>, Consumer<EntryConsumer>> sc) {
    testWithEntryConsumer(sc.apply(ss.get()));

    Spliterator<Map.Entry<Integer, Integer>> s = ss.get();
    Spliterator<Map.Entry<Integer, Integer>> split = s.trySplit();
    if (split != null) {
        testWithEntryConsumer(sc.apply(split));
        testWithEntryConsumer(sc.apply(s));
    }
}

Example 15

Source File: UnmodifiableMapEntrySet.java From openjdk-jdk8u-backup with GNU General Public License v2.0

5 votes

void testSpliterator(Supplier<Spliterator<Map.Entry<Integer, Integer>>> ss,
                     // Higher order function that given a spliterator returns a
                     // consumer for that spliterator which traverses elements
                     // using an EntryConsumer
                     Function<Spliterator<Map.Entry<Integer, Integer>>, Consumer<EntryConsumer>> sc) {
    testWithEntryConsumer(sc.apply(ss.get()));

    Spliterator<Map.Entry<Integer, Integer>> s = ss.get();
    Spliterator<Map.Entry<Integer, Integer>> split = s.trySplit();
    if (split != null) {
        testWithEntryConsumer(sc.apply(split));
        testWithEntryConsumer(sc.apply(s));
    }
}

Example 16

Source File: SpliteratorTestHelper.java From dragonwell8_jdk with GNU General Public License v2.0

5 votes

private static <T, S extends Spliterator<T>> void testSplitOnce(
        Collection<T> exp,
        Supplier<S> supplier,
        UnaryOperator<Consumer<T>> boxingAdapter,
        ContentAsserter<T> asserter) {
    S spliterator = supplier.get();
    long sizeIfKnown = spliterator.getExactSizeIfKnown();
    boolean isOrdered = spliterator.hasCharacteristics(Spliterator.ORDERED);

    ArrayList<T> fromSplit = new ArrayList<>();
    Spliterator<T> s1 = supplier.get();
    Spliterator<T> s2 = s1.trySplit();
    long s1Size = s1.getExactSizeIfKnown();
    long s2Size = (s2 != null) ? s2.getExactSizeIfKnown() : 0;
    Consumer<T> addToFromSplit = boxingAdapter.apply(fromSplit::add);
    if (s2 != null)
        s2.forEachRemaining(addToFromSplit);
    s1.forEachRemaining(addToFromSplit);

    if (sizeIfKnown >= 0) {
        assertEquals(sizeIfKnown, fromSplit.size());
        if (s1Size >= 0 && s2Size >= 0)
            assertEquals(sizeIfKnown, s1Size + s2Size);
    }

    asserter.assertContents(fromSplit, exp, isOrdered);
}

Example 17

Source File: SpliteratorCollisions.java From TencentKona-8 with GNU General Public License v2.0

4 votes

private static <T> void testSplitUntilNull(SplitNode<T> e) {
    // Use an explicit stack to avoid a StackOverflowException when testing a Spliterator
    // that when repeatedly split produces a right-balanced (and maybe degenerate) tree, or
    // for a spliterator that is badly behaved.
    Deque<SplitNode<T>> stack = new ArrayDeque<>();
    stack.push(e);

    int iteration = 0;
    while (!stack.isEmpty()) {
        assertTrue(iteration++ < MAXIMUM_STACK_CAPACITY, "Exceeded maximum stack modification count of 1 << 18");

        e = stack.pop();
        Spliterator<T> parentAndRightSplit = e.s;

        long parentEstimateSize = parentAndRightSplit.estimateSize();
        assertTrue(parentEstimateSize >= 0,
                   String.format("Split size estimate %d < 0", parentEstimateSize));

        long parentSize = parentAndRightSplit.getExactSizeIfKnown();
        Spliterator<T> leftSplit = parentAndRightSplit.trySplit();
        if (leftSplit == null) {
            parentAndRightSplit.forEachRemaining(e.c);
            continue;
        }

        assertSpliterator(leftSplit, e.rootCharacteristics);
        assertSpliterator(parentAndRightSplit, e.rootCharacteristics);

        if (parentEstimateSize != Long.MAX_VALUE && leftSplit.estimateSize() > 0 && parentAndRightSplit.estimateSize() > 0) {
            assertTrue(leftSplit.estimateSize() < parentEstimateSize,
                       String.format("Left split size estimate %d >= parent split size estimate %d", leftSplit.estimateSize(), parentEstimateSize));
            assertTrue(parentAndRightSplit.estimateSize() < parentEstimateSize,
                       String.format("Right split size estimate %d >= parent split size estimate %d", leftSplit.estimateSize(), parentEstimateSize));
        }
        else {
            assertTrue(leftSplit.estimateSize() <= parentEstimateSize,
                       String.format("Left split size estimate %d > parent split size estimate %d", leftSplit.estimateSize(), parentEstimateSize));
            assertTrue(parentAndRightSplit.estimateSize() <= parentEstimateSize,
                       String.format("Right split size estimate %d > parent split size estimate %d", leftSplit.estimateSize(), parentEstimateSize));
        }

        long leftSize = leftSplit.getExactSizeIfKnown();
        long rightSize = parentAndRightSplit.getExactSizeIfKnown();
        if (parentSize >= 0 && leftSize >= 0 && rightSize >= 0)
            assertEquals(parentSize, leftSize + rightSize,
                         String.format("exact left split size %d + exact right split size %d != parent exact split size %d",
                                       leftSize, rightSize, parentSize));

        // Add right side to stack first so left side is popped off first
        stack.push(e.fromSplit(parentAndRightSplit));
        stack.push(e.fromSplit(leftSplit));
    }
}

Example 18

Source File: Main.java From Java-Coding-Problems with MIT License

4 votes

public static void main(String[] args) throws IOException {
    
    String str = "Character Information 字 Development and Maintenance "
            + "Project 盤 for e-Government MojiJoho-Kiban 事 Project";
            
    Spliterator<Character> spliterator = new IdeographicSpliterator(str);
    Stream<Character> stream = StreamSupport.stream(spliterator, true);
    
    // force spliterator to do its job
    stream.collect(Collectors.toList());
            
    System.out.println("\n---------------------------------------------\n");
    
    List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

    Spliterator<Integer> s1 = numbers.spliterator();

    s1.tryAdvance(e -> System.out.println("Advancing to the first element of s1: " + e));

    System.out.println("\nEstimated size of s1: " + s1.estimateSize());

    Spliterator<Integer> s2 = s1.trySplit();

    System.out.println("\nSplitting s1 ...");
    System.out.println("Estimated size s1: " + s1.estimateSize());
    System.out.println("Estimated size s2: " + s2.estimateSize());

    System.out.println("\nPrint remaining elements of s1:");
    s1.forEachRemaining(System.out::println);
    System.out.println("\nPrint remaining elements of s2:");
    s2.forEachRemaining(System.out::println);

    System.out.println("\nCharacteristics:");
    System.out.println(s1.characteristics());
    System.out.println(s2.characteristics());

    System.out.println("\nCheck that s1 is ordered:");
    if (s1.hasCharacteristics(Spliterator.ORDERED)) {
        System.out.println("ORDERED");
    }

    System.out.println("\nCheck that s1 is sized:");
    if (s1.hasCharacteristics(Spliterator.SIZED)) {
        System.out.println("SIZED");
    }         
}

Example 19

Source File: SpliteratorTestHelper.java From openjdk-jdk8u with GNU General Public License v2.0

4 votes

private static <T> void testSplitUntilNull(SplitNode<T> e) {
    // Use an explicit stack to avoid a StackOverflowException when testing a Spliterator
    // that when repeatedly split produces a right-balanced (and maybe degenerate) tree, or
    // for a spliterator that is badly behaved.
    Deque<SplitNode<T>> stack = new ArrayDeque<>();
    stack.push(e);

    int iteration = 0;
    while (!stack.isEmpty()) {
        assertTrue(iteration++ < MAXIMUM_STACK_CAPACITY, "Exceeded maximum stack modification count of 1 << 18");

        e = stack.pop();
        Spliterator<T> parentAndRightSplit = e.s;

        long parentEstimateSize = parentAndRightSplit.estimateSize();
        assertTrue(parentEstimateSize >= 0,
                   String.format("Split size estimate %d < 0", parentEstimateSize));

        long parentSize = parentAndRightSplit.getExactSizeIfKnown();
        Spliterator<T> leftSplit = parentAndRightSplit.trySplit();
        if (leftSplit == null) {
            parentAndRightSplit.forEachRemaining(e.c);
            continue;
        }

        assertSpliterator(leftSplit, e.rootCharacteristics);
        assertSpliterator(parentAndRightSplit, e.rootCharacteristics);

        if (parentEstimateSize != Long.MAX_VALUE && leftSplit.estimateSize() > 0
            && parentAndRightSplit.estimateSize() > 0) {
            assertTrue(leftSplit.estimateSize() < parentEstimateSize,
                       String.format("Left split size estimate %d >= parent split size estimate %d",
                                     leftSplit.estimateSize(), parentEstimateSize));
            assertTrue(parentAndRightSplit.estimateSize() < parentEstimateSize,
                       String.format("Right split size estimate %d >= parent split size estimate %d",
                                     leftSplit.estimateSize(), parentEstimateSize));
        }
        else {
            assertTrue(leftSplit.estimateSize() <= parentEstimateSize,
                       String.format("Left split size estimate %d > parent split size estimate %d",
                                     leftSplit.estimateSize(), parentEstimateSize));
            assertTrue(parentAndRightSplit.estimateSize() <= parentEstimateSize,
                       String.format("Right split size estimate %d > parent split size estimate %d",
                                     leftSplit.estimateSize(), parentEstimateSize));
        }

        long leftSize = leftSplit.getExactSizeIfKnown();
        long rightSize = parentAndRightSplit.getExactSizeIfKnown();
        if (parentSize >= 0 && leftSize >= 0 && rightSize >= 0)
            assertEquals(parentSize, leftSize + rightSize,
                         String.format("exact left split size %d + exact right split size %d != parent exact split size %d",
                                       leftSize, rightSize, parentSize));

        // Add right side to stack first so left side is popped off first
        stack.push(e.fromSplit(parentAndRightSplit));
        stack.push(e.fromSplit(leftSplit));
    }
}

Example 20

Source File: MoreStreams.java From mug with Apache License 2.0

4 votes

private static <F, T> T splitThenWrap(
    Spliterator<F> from, Function<? super Spliterator<F>, ? extends T> wrapper) {
  Spliterator<F> it = from.trySplit();
  return it == null ? null : wrapper.apply(it);
}