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• The Minimal Value Types project is an early prototype for Value Types
  • provides initial subset of Value Type functionality, essentially flattened data
  • provides  new a new type which is:
    • immutable, identity-agnostic, non-nullable, non-synchronizable, final
    • does not inherit from java.lang.Object

• • Arrays of value types are flattened
Derived Value Class can
• • Can contain primitives or references

Target Audience

• Power users  - Java/JVM Language, Framework, Library authors/exports
  • who are comfortable with early experimental software
  • who recognize that everything in the experiment - the model, the classfile extensions, the byte codes is likely to change
  • who want to contribute to early exploration of Value Types
  • who will not build any products based on these prototypes
• Who are willing to provide feedback to the developers on a subset of Value Type features
• Who will provide use cases for the development team to experiment with optimizations

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• Create a POJO using an experimental javac, with an annotation ValueCapableClass (jvm.internal.value.ValueCapableClass)
  • JVM will derive a Derived Value Class (DVC) from this defined "box" which we call the Value Capable Class (VCC)
  • DVC contains an immutable copy of the instance fields from the VCC
• Work with MethodHandles and experimental reflection package ValueType (jdk.experimental.value.ValueType)
• Or spin your own byte codes
  
  • experimental MethodBuilder (jdk/experimental/value.MethodHandleBuilder)
  • future: ASM support is planned

Test Examples

• See directory jdk/test/valhalla/mvt in your repository
  • e.g. MethodHandlesTest
• Command-line flags: Minimal Value Types Command line Options
  • java: use -Xverify:none -XX:+EnableMVT

Filing Bugs

• File openjdk bugs with synopsis starting with "[MVT]" and labels: "mvt"

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• Experimental Appendix for Java Virtual Machine Specification for Value Classes
• http://cr.openjdk.java.net/~chegar/docs/sandbox.html  // instructions for working with branch repositorieshttps://wiki.

• openjdk.java.net/display/valhalla/Minimal + Value +Types+and+Valhalla+value+types+command+line+options // MVT command-line optionsTypes Command line Options
• Youtube JVMLS 2017: Minimal Value Types: Origins and Programming Model
  
• Youtube JVMLS 2017: Minimal Value Types: Under the Hood
  

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