This page describes the command line for the java compiler the java launcher and HotSpot for the support of value types in the valhalla project.

javac

• -XDenableValueTypes
  Boolean value, default value is `false`
  Enable direct declaration and compilation of value type classes via the "__ByValue" and other qualifiers.
• -XDmangleClassInfo
  Boolean value, default value is `false`
  Ensure value type names are distinguishable a reference class names by prepending ";Q" to the value type name.
  Should be used in conjunction with java flag "valhalla.mangleClassInfo".
• -Xlint:values
  Lint category for warnings associated to bad usage of value capable classes - examples:
  • VCC not final
  • VCC cannot 'extend' another class
  • overrides of 'bad' Object methods (such as wait/notify)
  • illegal modifiers on VCC such as 'synchronized'
  • non-final instance fields in VCC
  • cannot assign 'null' to variable of VCC type
    
    

java

• -Djava.lang.invoke.MethodHandle.DUMP_CLASS_FILES
  Boolean value, default value is `false`
  If true dump class files generated for lambda forms and derived value types into a directory named DUMP_CLASS_FILES under the current directory
• -Dvalhalla.enableValueLambdaForms
  Boolean value, default value is `true`
  If true then lambda forms with value types in their signature will use the Q type __Value and value-type specific byte code will be generated.
• -Dvalhalla.enablePoolPatches
  Boolean value, default value is `false`
  If true and if "valhalla.enableValueLambdaForms" is true then lambda forms with value types in their signature will generate byte code with constant pool patching where appropriate
• -Dvalhalla.mangleClassInfo
  Boolean value, default value is `false`
  Ensure value type names are distinguishable a reference class names by prepending ";Q" to the value type name.
  Should be used in conjunction with javac flag "mangleClassInfo".

HotSpot

• -XX:EnableMVT
  Boolean value, default value is `false`
  If true enable support for minimal value types with a value capable class and an associated derived value type.
• -XX:EnableValhalla
  Boolean value, default value is `false`
  If true enable support for "valhalla" value types, which in contrast to MVT supports direct value types in conjunction with byte code generation or with the javac flag "enableValueTypes".
• -XX:ValueTypePassFieldsAsArgs
  Boolean value, default value is `false`
• -XX:ValueTypeReturnedAsFields
  Boolean value, default value is `false`
• -XX:ValueArrayFlatten
  Boolean value, default value is `false`
• -XX:ValueArrayElemMaxFlatSize
  Integer value
• -XX:ValueArrayElemMaxFlatOops
  Integer value