Module java.base

Package java.lang.foreign

Interface SequenceLayout

All Superinterfaces:

MemoryLayout

public sealed interface SequenceLayout
extends MemoryLayout

A compound layout that denotes a homogeneous repetition of a given element layout. The repetition count is said to be the sequence layout's element count. 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:

MemoryLayout.sequenceLayout(3, ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN));

is equivalent to the following layout:

MemoryLayout.structLayout(
    ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN),
    ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN),
    ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN));

Implementation Requirements:

This class is immutable, thread-safe and value-based.

Since:

22

Nested Class Summary

Nested classes/interfaces declared in interface java.lang.foreign.MemoryLayout

MemoryLayout.PathElement

Method Summary

Modifier and Type	Method	Description
long	elementCount()	Returns the element count of this sequence layout.
MemoryLayout	elementLayout()	Returns the element layout of this sequence layout.
SequenceLayout	flatten()	Returns a flattened sequence layout.
SequenceLayout	reshape(long... elementCounts)	Rearranges the elements in this sequence layout into a multidimensional sequence layout.
SequenceLayout	withByteAlignment(long byteAlignment)	Returns a memory layout with the same characteristics as this layout, but with the given alignment constraint (in bytes).
SequenceLayout	withElementCount(long elementCount)	Returns a sequence layout with the same characteristics of this layout, but with the given element count.
SequenceLayout	withName(String name)	Returns a memory layout with the same characteristics as this layout, but with the given name.

Methods declared in interface java.lang.foreign.MemoryLayout

arrayElementVarHandle, byteAlignment, byteOffset, byteOffsetHandle, byteSize, equals, hashCode, name, scale, scaleHandle, select, sliceHandle, toString, varHandle, withoutName

Method Details

elementLayout

MemoryLayout elementLayout()

Returns the element layout of this sequence layout.

Returns:

the element layout of this sequence layout

elementCount

long elementCount()

Returns the element count of this sequence layout.

Returns:

the element count of this sequence layout

withElementCount

SequenceLayout withElementCount(long elementCount)

Returns a sequence layout with the same characteristics of this layout, but with the given element count.

Parameters:

elementCount - the new element count

Returns:

a sequence layout with the same characteristics of this layout, but with the given element count

Throws:

IllegalArgumentException - if elementCount is negative

IllegalArgumentException - if elementLayout.bitSize() * elementCount overflows

reshape

SequenceLayout reshape(long... elementCounts)

Rearranges the elements in this sequence layout into a multidimensional sequence layout. The resulting layout is a sequence layout where element layouts in the 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.

For instance, given a sequence layout of the kind:

var seq = MemoryLayout.sequenceLayout(4, MemoryLayout.sequenceLayout(3, ValueLayout.JAVA_INT));

calling seq.reshape(2, 6) will yield the following sequence layout:

var reshapeSeq = MemoryLayout.sequenceLayout(2, MemoryLayout.sequenceLayout(6, ValueLayout.JAVA_INT));

If one of the provided element counts is the special value -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 reshapeSeq can also be computed in the following ways:

var reshapeSeqImplicit1 = seq.reshape(-1, 6);
var reshapeSeqImplicit2 = seq.reshape(2, -1);

Parameters:

elementCounts - an array of element counts, of which at most one can be -1

Returns:

a sequence layout where element layouts in the flattened projection of this sequence layout (see flatten()) are re-arranged into one or more nested sequence layouts

Throws:

IllegalArgumentException - if two or more element counts are set to -1, or if one or more element count is <= 0 (but other than -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

flatten

SequenceLayout flatten()

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:

MemoryLayout flatElementLayout(SequenceLayout sequenceLayout) {
   return switch (sequenceLayout.elementLayout()) {
       case SequenceLayout nestedSequenceLayout -> flatElementLayout(nestedSequenceLayout);
       case MemoryLayout layout -> layout;
   };
}

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:

var seq = MemoryLayout.sequenceLayout(4, MemoryLayout.sequenceLayout(3, ValueLayout.JAVA_INT));

calling seq.flatten() will yield the following sequence layout:

var flattenedSeq = MemoryLayout.sequenceLayout(12, ValueLayout.JAVA_INT);

Returns:

a sequence layout with the same size as this layout (but, possibly, with different element count), whose element layout is not a sequence layout

withName

SequenceLayout withName(String name)

Returns a memory layout with the same characteristics as this layout, but with the given name.

Specified by:

withName in interface MemoryLayout

Parameters:

name - the layout name

Returns:

a memory layout with the same characteristics as this layout, but with the given name

See Also:

• MemoryLayout.name()

withByteAlignment

SequenceLayout withByteAlignment(long byteAlignment)

Returns a memory layout with the same characteristics as this layout, but with the given alignment constraint (in bytes).

Specified by:

withByteAlignment in interface MemoryLayout

Parameters:

byteAlignment - the layout alignment constraint, expressed in bytes

Returns:

a memory layout with the same characteristics as this layout, but with the given alignment constraint (in bytes)

Throws:

IllegalArgumentException - if byteAlignment is not a power of two

IllegalArgumentException - if byteAlignment < elementLayout().byteAlignment()