5 ms·

I had heard a rumor that there ware talks of user defined value types. Does anyone know if there is any hope for this?

by stusmall 12y ago

quotemstr 12y ago
What JVM instructions would you use to implement user-defined value types?
- Padding 12y ago
  I'm not sure you'd need to introduce new instructions. "user-defined value types", i.e. structs, can already be done today by (ab)using the Flyweight pattern and storing data (possibly off-heap with RAII rather than GC semantics) in some byte[]. All a JDK-supplied implementation would really need to do is (1) automate/hide all the painful work necessary to set this up and (2) provide syntactic sugar in the form of operators that can directly manipulate members of these types (+fast implicitly inlined implementations of them, specialized on the member types).
danieldk 12y ago
It seems that it is almost in prototyping stage, the usual suspects have already written a sketch of a future proposal: http://cr.openjdk.java.net/~jrose/values/values.html http://cr.openjdk.java.net/~jrose/values/values.html
- stusmall 12y ago
  Awesome! Thanks. I don't know much about the path from idea to standardized feature with the JVM. Is there hope for it in Java 9 or is this much farther out in the future? Probably first and more importantly, what is the chance for this even ever happening?
  - hyperpape 12y ago
    "the path from idea to standardized feature" Guy Steele was asking for value types in 1998 (http://www.cs.virginia.edu/~evans/cs655/readings/steele.pdf http://www.cs.virginia.edu/~evans/cs655/readings/steele.pdf)
    - Padding 12y ago
      Yeah, but he was also asking for operator overloading.
      - hyperpape 12y ago
        Well, I don't have a problem with that, but it's not really relevant. The community liked one proposal and disliked the other, but it still took almost two decades to handle the one it liked.
        Padding 12y ago
        My point was that him simply liking/proposing it doesn't mean much.
  - karianna 12y ago
    Likely delivery timeframe for value types in Java 10. Definitely not Java 9. Source - many conversations with Brian Goetz et al.

I had heard a rumor that there ware talks of user defined value types. Does anyone know if there is any hope for this?

quotemstr 12y ago

What JVM instructions would you use to implement user-defined value types?

Padding 12y ago
I'm not sure you'd need to introduce new instructions. "user-defined value types", i.e. structs, can already be done today by (ab)using the Flyweight pattern and storing data (possibly off-heap with RAII rather than GC semantics) in some byte[]. All a JDK-supplied implementation would really need to do is (1) automate/hide all the painful work necessary to set this up and (2) provide syntactic sugar in the form of operators that can directly manipulate members of these types (+fast implicitly inlined implementations of them, specialized on the member types).

danieldk 12y ago

It seems that it is almost in prototyping stage, the usual suspects have already written a sketch of a future proposal: http://cr.openjdk.java.net/~jrose/values/values.html http://cr.openjdk.java.net/~jrose/values/values.html

stusmall 12y ago
Awesome! Thanks. I don't know much about the path from idea to standardized feature with the JVM. Is there hope for it in Java 9 or is this much farther out in the future? Probably first and more importantly, what is the chance for this even ever happening?
- hyperpape 12y ago
  "the path from idea to standardized feature" Guy Steele was asking for value types in 1998 (http://www.cs.virginia.edu/~evans/cs655/readings/steele.pdf http://www.cs.virginia.edu/~evans/cs655/readings/steele.pdf)
  - Padding 12y ago
    Yeah, but he was also asking for operator overloading.
    - hyperpape 12y ago
      Well, I don't have a problem with that, but it's not really relevant. The community liked one proposal and disliked the other, but it still took almost two decades to handle the one it liked.
      - Padding 12y ago
        My point was that him simply liking/proposing it doesn't mean much.
- karianna 12y ago
  Likely delivery timeframe for value types in Java 10. Definitely not Java 9. Source - many conversations with Brian Goetz et al.