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package java.util.stream;
import java.util.Spliterator;
import java.util.function.IntFunction;
/**
* Helper class for executing <a href="package-summary.html#StreamOps">
* stream pipelines</a>, capturing all of the information about a stream
* pipeline (output shape, intermediate operations, stream flags, parallelism,
* etc) in one place.
*
* <p>
* A {@code PipelineHelper} describes the initial segment of a stream pipeline,
* including its source, intermediate operations, and may additionally
* incorporate information about the terminal (or stateful) operation which
* follows the last intermediate operation described by this
* {@code PipelineHelper}. The {@code PipelineHelper} is passed to the
* {@link TerminalOp#evaluateParallel(PipelineHelper, java.util.Spliterator)},
* {@link TerminalOp#evaluateSequential(PipelineHelper, java.util.Spliterator)},
* and {@link AbstractPipeline#opEvaluateParallel(PipelineHelper, java.util.Spliterator,
* java.util.function.IntFunction)}, methods, which can use the
* {@code PipelineHelper} to access information about the pipeline such as
* head shape, stream flags, and size, and use the helper methods
* such as {@link #wrapAndCopyInto(Sink, Spliterator)},
* {@link #copyInto(Sink, Spliterator)}, and {@link #wrapSink(Sink)} to execute
* pipeline operations.
*
* @param <P_OUT> type of output elements from the pipeline
* @since 1.8
*/
abstract class PipelineHelper<P_OUT> {
/**
* Gets the stream shape for the source of the pipeline segment.
*
* @return the stream shape for the source of the pipeline segment.
*/
abstract StreamShape getSourceShape();
/**
* Gets the combined stream and operation flags for the output of the described
* pipeline. This will incorporate stream flags from the stream source, all
* the intermediate operations and the terminal operation.
*
* @return the combined stream and operation flags
* @see StreamOpFlag
*/
abstract int getStreamAndOpFlags();
/**
* Returns the exact output size of the portion of the output resulting from
* applying the pipeline stages described by this {@code PipelineHelper} to
* the the portion of the input described by the provided
* {@code Spliterator}, if known. If not known or known infinite, will
* return {@code -1}.
*
* @apiNote
* The exact output size is known if the {@code Spliterator} has the
* {@code SIZED} characteristic, and the operation flags
* {@link StreamOpFlag#SIZED} is known on the combined stream and operation
* flags.
*
* @param spliterator the spliterator describing the relevant portion of the
* source data
* @return the exact size if known, or -1 if infinite or unknown
*/
abstract<P_IN> long exactOutputSizeIfKnown(Spliterator<P_IN> spliterator);
/**
* Applies the pipeline stages described by this {@code PipelineHelper} to
* the provided {@code Spliterator} and send the results to the provided
* {@code Sink}.
*
* @implSpec
* The implementation behaves as if:
* <pre>{@code
* intoWrapped(wrapSink(sink), spliterator);
* }</pre>
*
* @param sink the {@code Sink} to receive the results
* @param spliterator the spliterator describing the source input to process
*/
abstract<P_IN, S extends Sink<P_OUT>> S wrapAndCopyInto(S sink, Spliterator<P_IN> spliterator);
/**
* Pushes elements obtained from the {@code Spliterator} into the provided
* {@code Sink}. If the stream pipeline is known to have short-circuiting
* stages in it (see {@link StreamOpFlag#SHORT_CIRCUIT}), the
* {@link Sink#cancellationRequested()} is checked after each
* element, stopping if cancellation is requested.
*
* @implSpec
* This method conforms to the {@code Sink} protocol of calling
* {@code Sink.begin} before pushing elements, via {@code Sink.accept}, and
* calling {@code Sink.end} after all elements have been pushed.
*
* @param wrappedSink the destination {@code Sink}
* @param spliterator the source {@code Spliterator}
*/
abstract<P_IN> void copyInto(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator);
/**
* Pushes elements obtained from the {@code Spliterator} into the provided
* {@code Sink}, checking {@link Sink#cancellationRequested()} after each
* element, and stopping if cancellation is requested.
*
* @implSpec
* This method conforms to the {@code Sink} protocol of calling
* {@code Sink.begin} before pushing elements, via {@code Sink.accept}, and
* calling {@code Sink.end} after all elements have been pushed or if
* cancellation is requested.
*
* @param wrappedSink the destination {@code Sink}
* @param spliterator the source {@code Spliterator}
*/
abstract <P_IN> void copyIntoWithCancel(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator);
/**
* Takes a {@code Sink} that accepts elements of the output type of the
* {@code PipelineHelper}, and wrap it with a {@code Sink} that accepts
* elements of the input type and implements all the intermediate operations
* described by this {@code PipelineHelper}, delivering the result into the
* provided {@code Sink}.
*
* @param sink the {@code Sink} to receive the results
* @return a {@code Sink} that implements the pipeline stages and sends
* results to the provided {@code Sink}
*/
abstract<P_IN> Sink<P_IN> wrapSink(Sink<P_OUT> sink);
/**
*
* @param spliterator
* @param <P_IN>
* @return
*/
abstract<P_IN> Spliterator<P_OUT> wrapSpliterator(Spliterator<P_IN> spliterator);
/**
* Constructs a @{link Node.Builder} compatible with the output shape of
* this {@code PipelineHelper}.
*
* @param exactSizeIfKnown if >=0 then a builder will be created that has a
* fixed capacity of exactly sizeIfKnown elements; if < 0 then the
* builder has variable capacity. A fixed capacity builder will fail
* if an element is added after the builder has reached capacity.
* @param generator a factory function for array instances
* @return a {@code Node.Builder} compatible with the output shape of this
* {@code PipelineHelper}
*/
abstract Node.Builder<P_OUT> makeNodeBuilder(long exactSizeIfKnown,
IntFunction<P_OUT[]> generator);
/**
* Collects all output elements resulting from applying the pipeline stages
* to the source {@code Spliterator} into a {@code Node}.
*
* @implNote
* If the pipeline has no intermediate operations and the source is backed
* by a {@code Node} then that {@code Node} will be returned (or flattened
* and then returned). This reduces copying for a pipeline consisting of a
* stateful operation followed by a terminal operation that returns an
* array, such as:
* <pre>{@code
* stream.sorted().toArray();
* }</pre>
*
* @param spliterator the source {@code Spliterator}
* @param flatten if true and the pipeline is a parallel pipeline then the
* {@code Node} returned will contain no children, otherwise the
* {@code Node} may represent the root in a tree that reflects the
* shape of the computation tree.
* @param generator a factory function for array instances
* @return the {@code Node} containing all output elements
*/
abstract<P_IN> Node<P_OUT> evaluate(Spliterator<P_IN> spliterator,
boolean flatten,
IntFunction<P_OUT[]> generator);
}