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• platforms: x64 Linux, x64 Mac OS X, Windows
• no support for value class with no instance fields
• no support for atomic fields containing value types
• no support for @Contended value type fields
• static fields are not flattenable
• no AOT, CDS, ZGC, serviceability agent
• -Xint and C2 only, no C1, no tiered-compilation, no Graal
• unsafe field and array accessor APIs are not supported for value types
  • VarHandles support value types
    • however: they do not enforce immutability  or non-nullability for value types
      • note that immutable types can be copied, so updates may not be seen
  • low-level unsafe APIs are UNSAFE and will not be changed to support value types
  • risks: If a value type has been flattened in a container, unsafe does not know the layout
    • getObject could return the first flattened element rather than the expected reference
• interpreter is not optimized, focus is on JIT optimization
• Please provide additional USE CASES for optimizations
• Working on additional test cases

Future Possibilities

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• LW1 updates: 
  • fix bugs, add optimizations and support for additional minor features
• LWX:
  • Addition of significant feature support
  • Addition of language level syntax and semantics
  • Eventually a preview with an openjdk release
  • Expect specialized generics and support for primitives as value types will have their own early access cycles 

How to Try L-World Value Types

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Target Audience

• Power users  - Java/JVM Language, Framework, Library authors/experts
  • 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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