Module java.base
Package java.lang.foreign

Interface MemoryLayout.PathElement

Enclosing interface:
MemoryLayoutPREVIEW
public static sealed interface MemoryLayout.PathElement
PathElement is a preview API of the Java platform.
Programs can only use PathElement when preview features are enabled.
Preview features may be removed in a future release, or upgraded to permanent features of the Java platform.
An element in a layout path. There are two kinds of path elements: group path elements and sequence path elements. Group path elements are used to select a named member layout within a GroupLayoutPREVIEW. Sequence path elements are used to select a sequence element layout within a SequenceLayoutPREVIEW; selection of sequence element layout can be explicit (see sequenceElement(long)) or implicit (see sequenceElement()). When a path uses one or more implicit sequence path elements, it acquires additional free dimensions.
Since:
19
Implementation Requirements:
Implementations of this interface are immutable, thread-safe and value-based.

  • Method Details

    • groupElement

      static MemoryLayout.PathElementPREVIEW groupElement(String name)
      Returns a path element which selects a member layout with the given name in a group layout. The path element returned by this method does not alter the number of free dimensions of any path that is combined with such element.
      Parameters:
      name - the name of the group element to be selected.
      Returns:
      a path element which selects the group element with the given name.
      Implementation Requirements:
      in case multiple group elements with a matching name exist, the path element returned by this method will select the first one; that is, the group element with the lowest offset from current path is selected.

    • sequenceElement

      static MemoryLayout.PathElementPREVIEW sequenceElement(long index)
      Returns a path element which selects the element layout at the specified position in a sequence layout. The path element returned by this method does not alter the number of free dimensions of any path that is combined with such element.
      Parameters:
      index - the index of the sequence element to be selected.
      Returns:
      a path element which selects the sequence element layout with the given index.
      Throws:
      IllegalArgumentException - if index < 0.

    • sequenceElement

      static MemoryLayout.PathElementPREVIEW sequenceElement(long start, long step)
      Returns a path element which selects the element layout in a range of positions in a sequence layout. The range is expressed as a pair of starting index (inclusive) S and step factor (which can also be negative) F.

      If a path with free dimensions n is combined with the path element returned by this method, the number of free dimensions of the resulting path will be 1 + n. If the free dimension associated with this path is bound by an index I, the resulting accessed offset can be obtained with the following formula: 

      
 E * (S + I * F)
      where E is the size (in bytes) of the sequence element layout.

      Additionally, if C is the sequence element count, it follows that 0 <= I < B, where B is computed as follows:

      • if F > 0, then B = ceilDiv(C - S, F)
      • if F < 0, then B = ceilDiv(-(S + 1), -F)
      Parameters:
      start - the index of the first sequence element to be selected.
      step - the step factor at which subsequence sequence elements are to be selected.
      Returns:
      a path element which selects the sequence element layout with the given index.
      Throws:
      IllegalArgumentException - if start < 0, or step == 0.

    • sequenceElement

      static MemoryLayout.PathElementPREVIEW sequenceElement()
      Returns a path element which selects an unspecified element layout in a sequence layout.

      If a path with free dimensions n is combined with the path element returned by this method, the number of free dimensions of the resulting path will be 1 + n. If the free dimension associated with this path is bound by an index I, the resulting accessed offset can be obtained with the following formula: 

      
 E * I
      where E is the size (in bytes) of the sequence element layout.

      Additionally, if C is the sequence element count, it follows that 0 <= I < C.

      Returns:
      a path element which selects an unspecified sequence element layout.