jdk/src/java.base/share/classes/java/lang/foreign/SequenceLayout.java

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package java.lang.foreign;

import jdk.internal.foreign.layout.SequenceLayoutImpl;
import jdk.internal.javac.PreviewFeature;

/**
 * A compound layout that denotes a homogeneous repetition of a given <em>element layout</em>.
 * The repetition count is said to be the sequence layout's <em>element count</em>. A sequence layout can be thought of as a
 * struct layout where the sequence layout's element layout is repeated a number of times that is equal to the sequence
 * layout's element count. In other words this layout:
 *
 * {@snippet lang=java :
 * MemoryLayout.sequenceLayout(3, ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN));
 * }
 *
 * is equivalent to the following layout:
 *
 * {@snippet lang=java :
 * MemoryLayout.structLayout(
 *     ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN),
 *     ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN),
 *     ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN));
 * }
 *
 * @implSpec
 * This class is immutable, thread-safe and <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>.
 *
 * @since 19
 */
@PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
public sealed interface SequenceLayout extends MemoryLayout permits SequenceLayoutImpl {


    /**
     * {@return the element layout of this sequence layout}
     */
    MemoryLayout elementLayout();

    /**
     * {@return the element count of this sequence layout}
     */
    long elementCount();

    /**
     * {@return a sequence layout with the same characteristics of this layout, but with the given element count}
     * @param elementCount the new element count.
     * @throws IllegalArgumentException if {@code elementCount} is negative.
     * @throws IllegalArgumentException if {@code elementLayout.bitSize() * elementCount} overflows.
     */
    SequenceLayout withElementCount(long elementCount);

    /**
     * Rearranges the elements in this sequence layout into a multi-dimensional sequence layout.
     * The resulting layout is a sequence layout where element layouts in the {@linkplain #flatten() flattened projection}
     * of this sequence layout are rearranged into one or more nested sequence layouts
     * according to the provided element counts. This transformation preserves the layout size;
     * that is, multiplying the provided element counts must yield the same element count
     * as the flattened projection of this sequence layout.
     * <p>
     * For instance, given a sequence layout of the kind:
     * {@snippet lang=java :
     * var seq = MemoryLayout.sequenceLayout(4, MemoryLayout.sequenceLayout(3, ValueLayout.JAVA_INT));
     * }
     * calling {@code seq.reshape(2, 6)} will yield the following sequence layout:
     * {@snippet lang=java :
     * var reshapeSeq = MemoryLayout.sequenceLayout(2, MemoryLayout.sequenceLayout(6, ValueLayout.JAVA_INT));
     * }
     * <p>
     * If one of the provided element count is the special value {@code -1}, then the element
     * count in that position will be inferred from the remaining element counts and the
     * element count of the flattened projection of this layout. For instance, a layout equivalent to
     * the above {@code reshapeSeq} can also be computed in the following ways:
     * {@snippet lang=java :
     * var reshapeSeqImplicit1 = seq.reshape(-1, 6);
     * var reshapeSeqImplicit2 = seq.reshape(2, -1);
     * }
     * @param elementCounts an array of element counts, of which at most one can be {@code -1}.
     * @return a sequence layout where element layouts in the {@linkplain #flatten() flattened projection} of this
     * sequence layout (see {@link #flatten()}) are re-arranged into one or more nested sequence layouts.
     * @throws IllegalArgumentException if two or more element counts are set to {@code -1}, or if one
     * or more element count is {@code <= 0} (but other than {@code -1}) or, if, after any required inference,
     * multiplying the element counts does not yield the same element count as the flattened projection of this
     * sequence layout.
     */
    SequenceLayout reshape(long... elementCounts);

    /**
     * Returns a flattened sequence layout. The element layout of the returned sequence layout
     * is the first non-sequence layout found by inspecting (recursively, if needed) the element layout of this sequence layout:
     * {@snippet lang=java :
     * MemoryLayout flatElementLayout(SequenceLayout sequenceLayout) {
     *    return switch (sequenceLayout.elementLayout()) {
     *        case SequenceLayout nestedSequenceLayout -> flatElementLayout(nestedSequenceLayout);
     *        case MemoryLayout layout -> layout;
     *    };
     * }
     * }
     * <p>
     * This transformation preserves the layout size; nested sequence layout in this sequence layout will
     * be dropped and their element counts will be incorporated into that of the returned sequence layout.
     * For instance, given a sequence layout of the kind:
     * {@snippet lang=java :
     * var seq = MemoryLayout.sequenceLayout(4, MemoryLayout.sequenceLayout(3, ValueLayout.JAVA_INT));
     * }
     * calling {@code seq.flatten()} will yield the following sequence layout:
     * {@snippet lang=java :
     * var flattenedSeq = MemoryLayout.sequenceLayout(12, ValueLayout.JAVA_INT);
     * }
     * @return a sequence layout with the same size as this layout (but, possibly, with different
     * element count), whose element layout is not a sequence layout.
     */
    SequenceLayout flatten();

    /**
     * {@inheritDoc}
     */
    @Override
    SequenceLayout withName(String name);

    /**
     * {@inheritDoc}
     */
    @Override
    MemoryLayout withoutName();

    /**
     * {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     * @throws IllegalArgumentException if {@code byteAlignment < elementLayout().byteAlignment()}.
     */
    SequenceLayout withByteAlignment(long byteAlignment);
}