/*
 * Hunt - A refined core library for D programming language.
 *
 * Copyright (C) 2018-2019 HuntLabs
 *
 * Website: https://www.huntlabs.net/
 *
 * Licensed under the Apache-2.0 License.
 *
 */

module hunt.util.Spliterator;


enum SpliteratorCharacteristic {
    /**
     * Characteristic value signifying that an encounter order is defined for
     * elements. If so, this Spliterator guarantees that method
     * {@link #trySplit} splits a strict prefix of elements, that method
     * {@link #tryAdvance} steps by one element in prefix order, and that
     * {@link #forEachRemaining} performs actions in encounter order.
     *
     * <p>A {@link Collection} has an encounter order if the corresponding
     * {@link Collection#iterator} documents an order. If so, the encounter
     * order is the same as the documented order. Otherwise, a collection does
     * not have an encounter order.
     *
     * @apiNote Encounter order is guaranteed to be ascending index order for
     * any {@link List}. But no order is guaranteed for hash-based collections
     * such as {@link HashSet}. Clients of a Spliterator that reports
     * {@code ORDERED} are expected to preserve ordering constraints in
     * non-commutative parallel computations.
     */
    ORDERED    = 0x00000010,

    /**
     * Characteristic value signifying that, for each pair of
     * encountered elements {@code x, y}, {@code !x.equals(y)}. This
     * applies for example, to a Spliterator based on a {@link Set}.
     */
    DISTINCT   = 0x00000001,

    /**
     * Characteristic value signifying that encounter order follows a defined
     * sort order. If so, method {@link #getComparator()} returns the associated
     * Comparator, or {@code null} if all elements are {@link Comparable} and
     * are sorted by their natural ordering.
     *
     * <p>A Spliterator that reports {@code SORTED} must also report
     * {@code ORDERED}.
     *
     * @apiNote The spliterators for {@code Collection} classes in the JDK that
     * implement {@link NavigableSet} or {@link SortedSet} report {@code SORTED}.
     */
    SORTED     = 0x00000004,

    /**
     * Characteristic value signifying that the value returned from
     * {@code estimateSize()} prior to traversal or splitting represents a
     * finite size that, in the absence of structural source modification,
     * represents an exact count of the number of elements that would be
     * encountered by a complete traversal.
     *
     * @apiNote Most Spliterators for Collections, that cover all elements of a
     * {@code Collection} report this characteristic. Sub-spliterators, such as
     * those for {@link HashSet}, that cover a sub-set of elements and
     * approximate their reported size do not.
     */
    SIZED      = 0x00000040,

    /**
     * Characteristic value signifying that the source guarantees that
     * encountered elements will not be {@code null}. (This applies,
     * for example, to most concurrent collections, queues, and maps.)
     */
    NONNULL    = 0x00000100,

    /**
     * Characteristic value signifying that the element source cannot be
     * structurally modified; that is, elements cannot be added, replaced, or
     * removed, so such changes cannot occur during traversal. A Spliterator
     * that does not report {@code IMMUTABLE} or {@code CONCURRENT} is expected
     * to have a documented policy (for example throwing
     * {@link ConcurrentModificationException}) concerning structural
     * interference detected during traversal.
     */
    IMMUTABLE  = 0x00000400,

    /**
     * Characteristic value signifying that the element source may be safely
     * concurrently modified (allowing additions, replacements, and/or removals)
     * by multiple threads without external synchronization. If so, the
     * Spliterator is expected to have a documented policy concerning the impact
     * of modifications during traversal.
     *
     * <p>A top-level Spliterator should not report both {@code CONCURRENT} and
     * {@code SIZED}, since the finite size, if known, may change if the source
     * is concurrently modified during traversal. Such a Spliterator is
     * inconsistent and no guarantees can be made about any computation using
     * that Spliterator. Sub-spliterators may report {@code SIZED} if the
     * sub-split size is known and additions or removals to the source are not
     * reflected when traversing.
     *
     * @apiNote Most concurrent collections maintain a consistency policy
     * guaranteeing accuracy with respect to elements present at the point of
     * Spliterator construction, but possibly not reflecting subsequent
     * additions or removals.
     */
    CONCURRENT = 0x00001000,

    /**
     * Characteristic value signifying that all Spliterators resulting from
     * {@code trySplit()} will be both {@link #SIZED} and {@link #SUBSIZED}.
     * (This means that all child Spliterators, whether direct or indirect, will
     * be {@code SIZED}.)
     *
     * <p>A Spliterator that does not report {@code SIZED} as required by
     * {@code SUBSIZED} is inconsistent and no guarantees can be made about any
     * computation using that Spliterator.
     *
     * @apiNote Some spliterators, such as the top-level spliterator for an
     * approximately balanced binary tree, will report {@code SIZED} but not
     * {@code SUBSIZED}, since it is common to know the size of the entire tree
     * but not the exact sizes of subtrees.
     */
    SUBSIZED = 0x00004000
}

/**
 * An object for traversing and partitioning elements of a source.  The source
 * of elements covered by a Spliterator could be, for example, an array, a
 * {@link Collection}, an IO channel, or a generator function.
 *
 * <p>A Spliterator may traverse elements individually ({@link
 * #tryAdvance tryAdvance()}) or sequentially in bulk
 * ({@link #forEachRemaining forEachRemaining()}).
 *
 * <p>A Spliterator may also partition off some of its elements (using
 * {@link #trySplit}) as another Spliterator, to be used in
 * possibly-parallel operations.  Operations using a Spliterator that
 * cannot split, or does so in a highly imbalanced or inefficient
 * manner, are unlikely to benefit from parallelism.  Traversal
 * and splitting exhaust elements; each Spliterator is useful for only a single
 * bulk computation.
 *
 * <p>A Spliterator also reports a set of {@link #characteristics()} of its
 * structure, source, and elements from among {@link #ORDERED},
 * {@link #DISTINCT}, {@link #SORTED}, {@link #SIZED}, {@link #NONNULL},
 * {@link #IMMUTABLE}, {@link #CONCURRENT}, and {@link #SUBSIZED}. These may
 * be employed by Spliterator clients to control, specialize or simplify
 * computation.  For example, a Spliterator for a {@link Collection} would
 * report {@code SIZED}, a Spliterator for a {@link Set} would report
 * {@code DISTINCT}, and a Spliterator for a {@link SortedSet} would also
 * report {@code SORTED}.  Characteristics are reported as a simple unioned bit
 * set.
 *
 * Some characteristics additionally constrain method behavior; for example if
 * {@code ORDERED}, traversal methods must conform to their documented ordering.
 * New characteristics may be defined in the future, so implementors should not
 * assign meanings to unlisted values.
 *
 * <p><a name="binding">A Spliterator that does not report {@code IMMUTABLE} or
 * {@code CONCURRENT} is expected to have a documented policy concerning:
 * when the spliterator <em>binds</em> to the element source; and detection of
 * structural interference of the element source detected after binding.</a>  A
 * <em>late-binding</em> Spliterator binds to the source of elements at the
 * point of first traversal, first split, or first query for estimated size,
 * rather than at the time the Spliterator is created.  A Spliterator that is
 * not <em>late-binding</em> binds to the source of elements at the point of
 * construction or first invocation of any method.  Modifications made to the
 * source prior to binding are reflected when the Spliterator is traversed.
 * After binding a Spliterator should, on a best-effort basis, throw
 * {@link ConcurrentModificationException} if structural interference is
 * detected.  Spliterators that do this are called <em>fail-fast</em>.  The
 * bulk traversal method ({@link #forEachRemaining forEachRemaining()}) of a
 * Spliterator may optimize traversal and check for structural interference
 * after all elements have been traversed, rather than checking per-element and
 * failing immediately.
 *
 * <p>Spliterators can provide an estimate of the number of remaining elements
 * via the {@link #estimateSize} method.  Ideally, as reflected in characteristic
 * {@link #SIZED}, this value corresponds exactly to the number of elements
 * that would be encountered in a successful traversal.  However, even when not
 * exactly known, an estimated value value may still be useful to operations
 * being performed on the source, such as helping to determine whether it is
 * preferable to split further or traverse the remaining elements sequentially.
 *
 * <p>Despite their obvious utility in parallel algorithms, spliterators are not
 * expected to be thread-safe; instead, implementations of parallel algorithms
 * using spliterators should ensure that the spliterator is only used by one
 * thread at a time.  This is generally easy to attain via <em>serial
 * thread-confinement</em>, which often is a natural consequence of typical
 * parallel algorithms that work by recursive decomposition.  A thread calling
 * {@link #trySplit()} may hand over the returned Spliterator to another thread,
 * which in turn may traverse or further split that Spliterator.  The behaviour
 * of splitting and traversal is undefined if two or more threads operate
 * concurrently on the same spliterator.  If the original thread hands a
 * spliterator off to another thread for processing, it is best if that handoff
 * occurs before any elements are consumed with {@link #tryAdvance(Consumer)
 * tryAdvance()}, as certain guarantees (such as the accuracy of
 * {@link #estimateSize()} for {@code SIZED} spliterators) are only valid before
 * traversal has begun.
 *
 * <p>Primitive subtype specializations of {@code Spliterator} are provided for
 * {@link OfInt int}, {@link OfLong long}, and {@link OfDouble double} values.
 * The subtype default implementations of
 * {@link Spliterator#tryAdvance(hunt.util.functional.Consumer)}
 * and {@link Spliterator#forEachRemaining(hunt.util.functional.Consumer)} box
 * primitive values to instances of their corresponding wrapper class.  Such
 * boxing may undermine any performance advantages gained by using the primitive
 * specializations.  To avoid boxing, the corresponding primitive-based methods
 * should be used.  For example,
 * {@link Spliterator.OfInt#tryAdvance(hunt.util.functional.IntConsumer)}
 * and {@link Spliterator.OfInt#forEachRemaining(hunt.util.functional.IntConsumer)}
 * should be used in preference to
 * {@link Spliterator.OfInt#tryAdvance(hunt.util.functional.Consumer)} and
 * {@link Spliterator.OfInt#forEachRemaining(hunt.util.functional.Consumer)}.
 * Traversal of primitive values using boxing-based methods
 * {@link #tryAdvance tryAdvance()} and
 * {@link #forEachRemaining(hunt.util.functional.Consumer) forEachRemaining()}
 * does not affect the order in which the values, transformed to boxed values,
 * are encountered.
 *
 * @apiNote
 * <p>Spliterators, like {@code Iterator}s, are for traversing the elements of
 * a source.  The {@code Spliterator} API was designed to support efficient
 * parallel traversal in addition to sequential traversal, by supporting
 * decomposition as well as single-element iteration.  In addition, the
 * protocol for accessing elements via a Spliterator is designed to impose
 * smaller per-element overhead than {@code Iterator}, and to avoid the inherent
 * race involved in having separate methods for {@code hasNext()} and
 * {@code next()}.
 *
 * <p>For mutable sources, arbitrary and non-deterministic behavior may occur if
 * the source is structurally interfered with (elements added, replaced, or
 * removed) between the time that the Spliterator binds to its data source and
 * the end of traversal.  For example, such interference will produce arbitrary,
 * non-deterministic results when using the {@code java.util.stream} framework.
 *
 * <p>Structural interference of a source can be managed in the following ways
 * (in approximate order of decreasing desirability):
 * <ul>
 * <li>The source cannot be structurally interfered with.
 * <br>For example, an instance of
 * {@link hunt.concurrency.CopyOnWriteArrayList} is an immutable source.
 * A Spliterator created from the source reports a characteristic of
 * {@code IMMUTABLE}.</li>
 * <li>The source manages concurrent modifications.
 * <br>For example, a key set of a {@link hunt.concurrency.ConcurrentHashMap}
 * is a concurrent source.  A Spliterator created from the source reports a
 * characteristic of {@code CONCURRENT}.</li>
 * <li>The mutable source provides a late-binding and fail-fast Spliterator.
 * <br>Late binding narrows the window during which interference can affect
 * the calculation; fail-fast detects, on a best-effort basis, that structural
 * interference has occurred after traversal has commenced and throws
 * {@link ConcurrentModificationException}.  For example, {@link ArrayList},
 * and many other non-concurrent {@code Collection} classes in the JDK, provide
 * a late-binding, fail-fast spliterator.</li>
 * <li>The mutable source provides a non-late-binding but fail-fast Spliterator.
 * <br>The source increases the likelihood of throwing
 * {@code ConcurrentModificationException} since the window of potential
 * interference is larger.</li>
 * <li>The mutable source provides a late-binding and non-fail-fast Spliterator.
 * <br>The source risks arbitrary, non-deterministic behavior after traversal
 * has commenced since interference is not detected.
 * </li>
 * <li>The mutable source provides a non-late-binding and non-fail-fast
 * Spliterator.
 * <br>The source increases the risk of arbitrary, non-deterministic behavior
 * since non-detected interference may occur after construction.
 * </li>
 * </ul>
 *
 * <p><b>Example.</b> Here is a class (not a very useful one, except
 * for illustration) that maintains an array in which the actual data
 * are held in even locations, and unrelated tag data are held in odd
 * locations. Its Spliterator ignores the tags.
 *
 * <pre> {@code
 * class TaggedArray!(T) {
 *   private final Object[] elements; // immutable after construction
 *   TaggedArray(T[] data, Object[] tags) {
 *     int size = data.length;
 *     if (tags.length != size) throw new IllegalArgumentException();
 *     this.elements = new Object[2 * size];
 *     for (int i = 0, j = 0; i < size; ++i) {
 *       elements[j++] = data[i];
 *       elements[j++] = tags[i];
 *     }
 *   }
 *
 *   public Spliterator!(T) spliterator() {
 *     return new TaggedArraySpliterator<>(elements, 0, elements.length);
 *   }
 *
 *   static class TaggedArraySpliterator!(T) : Spliterator!(T) {
 *     private final Object[] array;
 *     private int origin; // current index, advanced on split or traversal
 *     private final int fence; // one past the greatest index
 *
 *     TaggedArraySpliterator(Object[] array, int origin, int fence) {
 *       this.array = array; this.origin = origin; this.fence = fence;
 *     }
 *
 *     public void forEachRemaining(Consumer!(T) action) {
 *       for (; origin < fence; origin += 2)
 *         action.accept((T) array[origin]);
 *     }
 *
 *     public bool tryAdvance(Consumer!(T) action) {
 *       if (origin < fence) {
 *         action.accept((T) array[origin]);
 *         origin += 2;
 *         return true;
 *       }
 *       else // cannot advance
 *         return false;
 *     }
 *
 *     public Spliterator!(T) trySplit() {
 *       int lo = origin; // divide range in half
 *       int mid = ((lo + fence) >>> 1) & ~1; // force midpoint to be even
 *       if (lo < mid) { // split out left half
 *         origin = mid; // reset this Spliterator's origin
 *         return new TaggedArraySpliterator<>(array, lo, mid);
 *       }
 *       else       // too small to split
 *         return null;
 *     }
 *
 *     public long estimateSize() {
 *       return (long)((fence - origin) / 2);
 *     }
 *
 *     public int characteristics() {
 *       return ORDERED | SIZED | IMMUTABLE | SUBSIZED;
 *     }
 *   }
 * }}</pre>
 *
 * <p>As an example how a parallel computation framework, such as the
 * {@code java.util.stream} package, would use Spliterator in a parallel
 * computation, here is one way to implement an associated parallel forEach,
 * that illustrates the primary usage idiom of splitting off subtasks until
 * the estimated amount of work is small enough to perform
 * sequentially. Here we assume that the order of processing across
 * subtasks doesn't matter; different (forked) tasks may further split
 * and process elements concurrently in undetermined order.  This
 * example uses a {@link hunt.concurrency.CountedCompleter};
 * similar usages apply to other parallel task constructions.
 *
 * <pre>{@code
 * static !(T) void parEach(TaggedArray!(T) a, Consumer!(T) action) {
 *   Spliterator!(T) s = a.spliterator();
 *   long targetBatchSize = s.estimateSize() / (ForkJoinPool.getCommonPoolParallelism() * 8);
 *   new ParEach(null, s, action, targetBatchSize).invoke();
 * }
 *
 * static class ParEach!(T) extends CountedCompleter!(void) {
 *   final Spliterator!(T) spliterator;
 *   final Consumer!(T) action;
 *   final long targetBatchSize;
 *
 *   ParEach(ParEach!(T) parent, Spliterator!(T) spliterator,
 *           Consumer!(T) action, long targetBatchSize) {
 *     super(parent);
 *     this.spliterator = spliterator; this.action = action;
 *     this.targetBatchSize = targetBatchSize;
 *   }
 *
 *   public void compute() {
 *     Spliterator!(T) sub;
 *     while (spliterator.estimateSize() > targetBatchSize &&
 *            (sub = spliterator.trySplit()) !is null) {
 *       addToPendingCount(1);
 *       new ParEach<>(this, sub, action, targetBatchSize).fork();
 *     }
 *     spliterator.forEachRemaining(action);
 *     propagateCompletion();
 *   }
 * }}</pre>
 *
 * @implNote
 * If the bool system property {@code org.openjdk.java.util.stream.tripwire}
 * is set to {@code true} then diagnostic warnings are reported if boxing of
 * primitive values occur when operating on primitive subtype specializations.
 *
 * @param (T) the type of elements returned by this Spliterator
 *
 * @see Collection
 */
interface Spliterator(T) {
//     /**
//      * If a remaining element exists, performs the given action on it,
//      * returning {@code true}; else returns {@code false}.  If this
//      * Spliterator is {@link #ORDERED} the action is performed on the
//      * next element in encounter order.  Exceptions thrown by the
//      * action are relayed to the caller.
//      *
//      * @param action The action
//      * @return {@code false} if no remaining elements existed
//      * upon entry to this method, else {@code true}.
//      * @throws NullPointerException if the specified action is null
//      */
//     bool tryAdvance(Consumer!(T) action);

//     /**
//      * Performs the given action for each remaining element, sequentially in
//      * the current thread, until all elements have been processed or the action
//      * throws an exception.  If this Spliterator is {@link #ORDERED}, actions
//      * are performed in encounter order.  Exceptions thrown by the action
//      * are relayed to the caller.
//      *
//      * @implSpec
//      * The default implementation repeatedly invokes {@link #tryAdvance} until
//      * it returns {@code false}.  It should be overridden whenever possible.
//      *
//      * @param action The action
//      * @throws NullPointerException if the specified action is null
//      */
//     default void forEachRemaining(Consumer!(T) action) {
//         do { } while (tryAdvance(action));
//     }

//     /**
//      * If this spliterator can be partitioned, returns a Spliterator
//      * covering elements, that will, upon return from this method, not
//      * be covered by this Spliterator.
//      *
//      * <p>If this Spliterator is {@link #ORDERED}, the returned Spliterator
//      * must cover a strict prefix of the elements.
//      *
//      * <p>Unless this Spliterator covers an infinite number of elements,
//      * repeated calls to {@code trySplit()} must eventually return {@code null}.
//      * Upon non-null return:
//      * <ul>
//      * <li>the value reported for {@code estimateSize()} before splitting,
//      * must, after splitting, be greater than or equal to {@code estimateSize()}
//      * for this and the returned Spliterator; and</li>
//      * <li>if this Spliterator is {@code SUBSIZED}, then {@code estimateSize()}
//      * for this spliterator before splitting must be equal to the sum of
//      * {@code estimateSize()} for this and the returned Spliterator after
//      * splitting.</li>
//      * </ul>
//      *
//      * <p>This method may return {@code null} for any reason,
//      * including emptiness, inability to split after traversal has
//      * commenced, data structure constraints, and efficiency
//      * considerations.
//      *
//      * @apiNote
//      * An ideal {@code trySplit} method efficiently (without
//      * traversal) divides its elements exactly in half, allowing
//      * balanced parallel computation.  Many departures from this ideal
//      * remain highly effective; for example, only approximately
//      * splitting an approximately balanced tree, or for a tree in
//      * which leaf nodes may contain either one or two elements,
//      * failing to further split these nodes.  However, large
//      * deviations in balance and/or overly inefficient {@code
//      * trySplit} mechanics typically result in poor parallel
//      * performance.
//      *
//      * @return a {@code Spliterator} covering some portion of the
//      * elements, or {@code null} if this spliterator cannot be split
//      */
//     Spliterator!(T) trySplit();

//     /**
//      * Returns an estimate of the number of elements that would be
//      * encountered by a {@link #forEachRemaining} traversal, or returns {@link
//      * Long#MAX_VALUE} if infinite, unknown, or too expensive to compute.
//      *
//      * <p>If this Spliterator is {@link #SIZED} and has not yet been partially
//      * traversed or split, or this Spliterator is {@link #SUBSIZED} and has
//      * not yet been partially traversed, this estimate must be an accurate
//      * count of elements that would be encountered by a complete traversal.
//      * Otherwise, this estimate may be arbitrarily inaccurate, but must decrease
//      * as specified across invocations of {@link #trySplit}.
//      *
//      * @apiNote
//      * Even an inexact estimate is often useful and inexpensive to compute.
//      * For example, a sub-spliterator of an approximately balanced binary tree
//      * may return a value that estimates the number of elements to be half of
//      * that of its parent; if the root Spliterator does not maintain an
//      * accurate count, it could estimate size to be the power of two
//      * corresponding to its maximum depth.
//      *
//      * @return the estimated size, or {@code Long.MAX_VALUE} if infinite,
//      *         unknown, or too expensive to compute.
//      */
//     long estimateSize();

//     /**
//      * Convenience method that returns {@link #estimateSize()} if this
//      * Spliterator is {@link #SIZED}, else {@code -1}.
//      * @implSpec
//      * The default implementation returns the result of {@code estimateSize()}
//      * if the Spliterator reports a characteristic of {@code SIZED}, and
//      * {@code -1} otherwise.
//      *
//      * @return the exact size, if known, else {@code -1}.
//      */
//     default long getExactSizeIfKnown() {
//         return (characteristics() & SIZED) == 0 ? -1L : estimateSize();
//     }

//     /**
//      * Returns a set of characteristics of this Spliterator and its
//      * elements. The result is represented as ORed values from {@link
//      * #ORDERED}, {@link #DISTINCT}, {@link #SORTED}, {@link #SIZED},
//      * {@link #NONNULL}, {@link #IMMUTABLE}, {@link #CONCURRENT},
//      * {@link #SUBSIZED}.  Repeated calls to {@code characteristics()} on
//      * a given spliterator, prior to or in-between calls to {@code trySplit},
//      * should always return the same result.
//      *
//      * <p>If a Spliterator reports an inconsistent set of
//      * characteristics (either those returned from a single invocation
//      * or across multiple invocations), no guarantees can be made
//      * about any computation using this Spliterator.
//      *
//      * @apiNote The characteristics of a given spliterator before splitting
//      * may differ from the characteristics after splitting.  For specific
//      * examples see the characteristic values {@link #SIZED}, {@link #SUBSIZED}
//      * and {@link #CONCURRENT}.
//      *
//      * @return a representation of characteristics
//      */
//     int characteristics();

//     /**
//      * Returns {@code true} if this Spliterator's {@link
//      * #characteristics} contain all of the given characteristics.
//      *
//      * @implSpec
//      * The default implementation returns true if the corresponding bits
//      * of the given characteristics are set.
//      *
//      * @param characteristics the characteristics to check for
//      * @return {@code true} if all the specified characteristics are present,
//      * else {@code false}
//      */
//     default bool hasCharacteristics(int characteristics) {
//         return (characteristics() & characteristics) == characteristics;
//     }

//     /**
//      * If this Spliterator's source is {@link #SORTED} by a {@link Comparator},
//      * returns that {@code Comparator}. If the source is {@code SORTED} in
//      * {@linkplain Comparable natural order}, returns {@code null}.  Otherwise,
//      * if the source is not {@code SORTED}, throws {@link IllegalStateException}.
//      *
//      * @implSpec
//      * The default implementation always throws {@link IllegalStateException}.
//      *
//      * @return a Comparator, or {@code null} if the elements are sorted in the
//      * natural order.
//      * @throws IllegalStateException if the spliterator does not report
//      *         a characteristic of {@code SORTED}.
//      */
//     default Comparator<T> getComparator() {
//         throw new IllegalStateException();
//     }



//     /**
//      * A Spliterator specialized for primitive values.
//      *
//      * @param (T) the type of elements returned by this Spliterator.  The
//      * type must be a wrapper type for a primitive type, such as {@code Integer}
//      * for the primitive {@code int} type.
//      * @param <T_CONS> the type of primitive consumer.  The type must be a
//      * primitive specialization of {@link hunt.util.functional.Consumer} for
//      * {@code T}, such as {@link hunt.util.functional.IntConsumer} for
//      * {@code Integer}.
//      * @param <T_SPLITR> the type of primitive Spliterator.  The type must be
//      * a primitive specialization of Spliterator for {@code T}, such as
//      * {@link Spliterator.OfInt} for {@code Integer}.
//      *
//      * @see Spliterator.OfInt
//      * @see Spliterator.OfLong
//      * @see Spliterator.OfDouble
//      * @since 1.8
//      */
//     public interface OfPrimitive<T, T_CONS, T_SPLITR extends Spliterator.OfPrimitive<T, T_CONS, T_SPLITR>>
//             extends Spliterator!(T) {
//         @Override
//         T_SPLITR trySplit();

//         /**
//          * If a remaining element exists, performs the given action on it,
//          * returning {@code true}; else returns {@code false}.  If this
//          * Spliterator is {@link #ORDERED} the action is performed on the
//          * next element in encounter order.  Exceptions thrown by the
//          * action are relayed to the caller.
//          *
//          * @param action The action
//          * @return {@code false} if no remaining elements existed
//          * upon entry to this method, else {@code true}.
//          * @throws NullPointerException if the specified action is null
//          */
//     
//         bool tryAdvance(T_CONS action);

//         /**
//          * Performs the given action for each remaining element, sequentially in
//          * the current thread, until all elements have been processed or the
//          * action throws an exception.  If this Spliterator is {@link #ORDERED},
//          * actions are performed in encounter order.  Exceptions thrown by the
//          * action are relayed to the caller.
//          *
//          * @implSpec
//          * The default implementation repeatedly invokes {@link #tryAdvance}
//          * until it returns {@code false}.  It should be overridden whenever
//          * possible.
//          *
//          * @param action The action
//          * @throws NullPointerException if the specified action is null
//          */
//     
//         default void forEachRemaining(T_CONS action) {
//             do { } while (tryAdvance(action));
//         }
//     }

//     /**
//      * A Spliterator specialized for {@code int} values.
//      * @since 1.8
//      */
//     public interface OfInt extends OfPrimitive<Integer, IntConsumer, OfInt> {

//         @Override
//         OfInt trySplit();

//         @Override
//         bool tryAdvance(IntConsumer action);

//         @Override
//         default void forEachRemaining(IntConsumer action) {
//             do { } while (tryAdvance(action));
//         }

//         /**
//          * {@inheritDoc}
//          * @implSpec
//          * If the action is an instance of {@code IntConsumer} then it is cast
//          * to {@code IntConsumer} and passed to
//          * {@link #tryAdvance(hunt.util.functional.IntConsumer)}; otherwise
//          * the action is adapted to an instance of {@code IntConsumer}, by
//          * boxing the argument of {@code IntConsumer}, and then passed to
//          * {@link #tryAdvance(hunt.util.functional.IntConsumer)}.
//          */
//         @Override
//         default bool tryAdvance(Consumer<Integer> action) {
//             if (action instanceof IntConsumer) {
//                 return tryAdvance((IntConsumer) action);
//             }
//             else {
//                 if (Tripwire.ENABLED)
//                     Tripwire.trip(getClass(),
//                                   "{0} calling Spliterator.OfInt.tryAdvance((IntConsumer) action::accept)");
//                 return tryAdvance((IntConsumer) action::accept);
//             }
//         }

//         /**
//          * {@inheritDoc}
//          * @implSpec
//          * If the action is an instance of {@code IntConsumer} then it is cast
//          * to {@code IntConsumer} and passed to
//          * {@link #forEachRemaining(hunt.util.functional.IntConsumer)}; otherwise
//          * the action is adapted to an instance of {@code IntConsumer}, by
//          * boxing the argument of {@code IntConsumer}, and then passed to
//          * {@link #forEachRemaining(hunt.util.functional.IntConsumer)}.
//          */
//         @Override
//         default void forEachRemaining(Consumer<Integer> action) {
//             if (action instanceof IntConsumer) {
//                 forEachRemaining((IntConsumer) action);
//             }
//             else {
//                 if (Tripwire.ENABLED)
//                     Tripwire.trip(getClass(),
//                                   "{0} calling Spliterator.OfInt.forEachRemaining((IntConsumer) action::accept)");
//                 forEachRemaining((IntConsumer) action::accept);
//             }
//         }
//     }

//     /**
//      * A Spliterator specialized for {@code long} values.
//      * @since 1.8
//      */
//     public interface OfLong extends OfPrimitive<Long, LongConsumer, OfLong> {

//         @Override
//         OfLong trySplit();

//         @Override
//         bool tryAdvance(LongConsumer action);

//         @Override
//         default void forEachRemaining(LongConsumer action) {
//             do { } while (tryAdvance(action));
//         }

//         /**
//          * {@inheritDoc}
//          * @implSpec
//          * If the action is an instance of {@code LongConsumer} then it is cast
//          * to {@code LongConsumer} and passed to
//          * {@link #tryAdvance(hunt.util.functional.LongConsumer)}; otherwise
//          * the action is adapted to an instance of {@code LongConsumer}, by
//          * boxing the argument of {@code LongConsumer}, and then passed to
//          * {@link #tryAdvance(hunt.util.functional.LongConsumer)}.
//          */
//         @Override
//         default bool tryAdvance(Consumer<Long> action) {
//             if (action instanceof LongConsumer) {
//                 return tryAdvance((LongConsumer) action);
//             }
//             else {
//                 if (Tripwire.ENABLED)
//                     Tripwire.trip(getClass(),
//                                   "{0} calling Spliterator.OfLong.tryAdvance((LongConsumer) action::accept)");
//                 return tryAdvance((LongConsumer) action::accept);
//             }
//         }

//         /**
//          * {@inheritDoc}
//          * @implSpec
//          * If the action is an instance of {@code LongConsumer} then it is cast
//          * to {@code LongConsumer} and passed to
//          * {@link #forEachRemaining(hunt.util.functional.LongConsumer)}; otherwise
//          * the action is adapted to an instance of {@code LongConsumer}, by
//          * boxing the argument of {@code LongConsumer}, and then passed to
//          * {@link #forEachRemaining(hunt.util.functional.LongConsumer)}.
//          */
//         @Override
//         default void forEachRemaining(Consumer<Long> action) {
//             if (action instanceof LongConsumer) {
//                 forEachRemaining((LongConsumer) action);
//             }
//             else {
//                 if (Tripwire.ENABLED)
//                     Tripwire.trip(getClass(),
//                                   "{0} calling Spliterator.OfLong.forEachRemaining((LongConsumer) action::accept)");
//                 forEachRemaining((LongConsumer) action::accept);
//             }
//         }
//     }

//     /**
//      * A Spliterator specialized for {@code double} values.
//      * @since 1.8
//      */
//     public interface OfDouble extends OfPrimitive<Double, DoubleConsumer, OfDouble> {

//         @Override
//         OfDouble trySplit();

//         @Override
//         bool tryAdvance(DoubleConsumer action);

//         @Override
//         default void forEachRemaining(DoubleConsumer action) {
//             do { } while (tryAdvance(action));
//         }

//         /**
//          * {@inheritDoc}
//          * @implSpec
//          * If the action is an instance of {@code DoubleConsumer} then it is
//          * cast to {@code DoubleConsumer} and passed to
//          * {@link #tryAdvance(hunt.util.functional.DoubleConsumer)}; otherwise
//          * the action is adapted to an instance of {@code DoubleConsumer}, by
//          * boxing the argument of {@code DoubleConsumer}, and then passed to
//          * {@link #tryAdvance(hunt.util.functional.DoubleConsumer)}.
//          */
//         @Override
//         default bool tryAdvance(Consumer<Double> action) {
//             if (action instanceof DoubleConsumer) {
//                 return tryAdvance((DoubleConsumer) action);
//             }
//             else {
//                 if (Tripwire.ENABLED)
//                     Tripwire.trip(getClass(),
//                                   "{0} calling Spliterator.OfDouble.tryAdvance((DoubleConsumer) action::accept)");
//                 return tryAdvance((DoubleConsumer) action::accept);
//             }
//         }

//         /**
//          * {@inheritDoc}
//          * @implSpec
//          * If the action is an instance of {@code DoubleConsumer} then it is
//          * cast to {@code DoubleConsumer} and passed to
//          * {@link #forEachRemaining(hunt.util.functional.DoubleConsumer)};
//          * otherwise the action is adapted to an instance of
//          * {@code DoubleConsumer}, by boxing the argument of
//          * {@code DoubleConsumer}, and then passed to
//          * {@link #forEachRemaining(hunt.util.functional.DoubleConsumer)}.
//          */
//         @Override
//         default void forEachRemaining(Consumer<Double> action) {
//             if (action instanceof DoubleConsumer) {
//                 forEachRemaining((DoubleConsumer) action);
//             }
//             else {
//                 if (Tripwire.ENABLED)
//                     Tripwire.trip(getClass(),
//                                   "{0} calling Spliterator.OfDouble.forEachRemaining((DoubleConsumer) action::accept)");
//                 forEachRemaining((DoubleConsumer) action::accept);
//             }
//         }
//     }
}