Class ValueLayout

java.lang.Object
jdk.incubator.foreign.ValueLayout
All Implemented Interfaces:
Constable, MemoryLayout

public final class ValueLayout
extends Object
implements MemoryLayout
A value layout. A value layout is used to model the memory layout associated with values of basic data types, such as integral types (either signed or unsigned) and floating-point types. Each value layout has a size and a byte order (see ByteOrder).

This is a value-based class; use of identity-sensitive operations (including reference equality (==), identity hash code, or synchronization) on instances of ValueLayout may have unpredictable results and should be avoided. The equals method should be used for comparisons.

Implementation Requirements:
This class is immutable and thread-safe.
  • Method Details

    • order

      public ByteOrder order()
      Returns the value's byte order.
      Returns:
      the value's byte order.
    • withOrder

      public ValueLayout withOrder​(ByteOrder order)
      Returns a new value layout with given byte order.
      Parameters:
      order - the desired byte order.
      Returns:
      a new value layout with given byte order.
    • describeConstable

      public Optional<DynamicConstantDesc<ValueLayout>> describeConstable()
      Description copied from interface: MemoryLayout
      Returns an Optional containing the nominal descriptor for this layout, if one can be constructed, or an empty Optional if one cannot be constructed.
      Specified by:
      describeConstable in interface Constable
      Specified by:
      describeConstable in interface MemoryLayout
      Returns:
      An Optional containing the resulting nominal descriptor, or an empty Optional if one cannot be constructed.
    • withName

      public ValueLayout withName​(String name)
      Creates a new layout which features the desired layout name.

      This is equivalent to the following code:

      
          withAttribute(LAYOUT_NAME, name);
       
      Specified by:
      withName in interface MemoryLayout
      Parameters:
      name - the layout name.
      Returns:
      a new layout which is the same as this layout, except for the name associated to it.
      See Also:
      MemoryLayout.name()
    • withBitAlignment

      public ValueLayout withBitAlignment​(long alignmentBits)
      Creates a new layout which features the desired alignment constraint.
      Specified by:
      withBitAlignment in interface MemoryLayout
      Parameters:
      alignmentBits - the layout alignment constraint, expressed in bits.
      Returns:
      a new layout which is the same as this layout, except for the alignment constraint associated to it.
    • withAttribute

      public ValueLayout withAttribute​(String name, Constable value)
      Returns a new memory layout which features the same attributes as this layout, plus the newly specified attribute. If this layout already contains an attribute with the same name, the existing attribute value is overwritten in the returned layout.
      Specified by:
      withAttribute in interface MemoryLayout
      Parameters:
      name - the attribute name.
      value - the attribute value.
      Returns:
      a new memory layout which features the same attributes as this layout, plus the newly specified attribute.
    • name

      public final Optional<String> name()
      Description copied from interface: MemoryLayout
      Return the name (if any) associated with this layout.

      This is equivalent to the following code:

      
          attribute(LAYOUT_NAME).map(String.class::cast);
       
      Specified by:
      name in interface MemoryLayout
      Returns:
      the layout name (if any).
      See Also:
      MemoryLayout.withName(String)
    • attribute

      public Optional<Constable> attribute​(String name)
      Description copied from interface: MemoryLayout
      Returns the attribute with the given name (if it exists).
      Specified by:
      attribute in interface MemoryLayout
      Parameters:
      name - the attribute name
      Returns:
      the attribute with the given name (if it exists).
    • attributes

      public Stream<String> attributes()
      Description copied from interface: MemoryLayout
      Returns a stream of the attribute names associated with this layout.
      Specified by:
      attributes in interface MemoryLayout
      Returns:
      a stream of the attribute names associated with this layout.
    • bitAlignment

      public final long bitAlignment()
      Description copied from interface: MemoryLayout
      Returns the alignment constraint associated with this layout, expressed in bits. Layout alignment defines a power of two A which is the bit-wise alignment of the layout. If A <= 8 then A/8 is the number of bytes that must be aligned for any pointer that correctly points to this layout. Thus:
      • A=8 means unaligned (in the usual sense), which is common in packets.
      • A=64 means word aligned (on LP64), A=32 int aligned, A=16 short aligned, etc.
      • A=512 is the most strict alignment required by the x86/SV ABI (for AVX-512 data).
      If no explicit alignment constraint was set on this layout (see MemoryLayout.withBitAlignment(long)), then this method returns the natural alignment constraint (in bits) associated with this layout.
      Specified by:
      bitAlignment in interface MemoryLayout
      Returns:
      the layout alignment constraint, in bits.
    • hasSize

      public boolean hasSize()
      Description copied from interface: MemoryLayout
      Does this layout have a specified size? A layout does not have a specified size if it is (or contains) a sequence layout whose size is unspecified (see SequenceLayout.elementCount()). Value layouts (see ValueLayout) and padding layouts (see MemoryLayout.ofPaddingBits(long)) always have a specified size, therefore this method always returns true in these cases.
      Specified by:
      hasSize in interface MemoryLayout
      Returns:
      true, if this layout has a specified size.
    • bitSize

      public long bitSize()
      Description copied from interface: MemoryLayout
      Computes the layout size, in bits.
      Specified by:
      bitSize in interface MemoryLayout
      Returns:
      the layout size, in bits.
    • isPadding

      public boolean isPadding()
      Description copied from interface: MemoryLayout
      Is this a padding layout (e.g. a layout created from MemoryLayout.ofPaddingBits(long)) ?
      Specified by:
      isPadding in interface MemoryLayout
      Returns:
      true, if this layout is a padding layout.