Valhalla EG 20191120

[David Simms]

- Brian
     - Expanding on the previous discussion on the Eclair model...
     - ...rather than having three things: references, inlines and 
primitives
         - lets subsume primitives (to be part in inline values)
         - ...so we get: reference values and inline values
     - Inline Values
         - primitives and inline classes
         - Represented and stored directly
     - Reference Values
         - Pointers to class instances, arrays and null
         - Represented and stored as indirections
     - More detail/write-up coming

- Remi: wait, is like MVT ?
- Brian: in the language yes, but not in the VM
     - Conversion is "free"
     - There are still Q-types, but L/Q-type (dual naming) is gone
     - "Companion interface"
- DanH: int vs interface (pox)
- Brian:
     - The language compiler will be doing the conversion i <=> 
Qjava.lang.int
     - There is a migration story for migrating primitives / Optional...
     - ...write-up need to be able to debate the finer points
- Remi: I kinda like it
- Brian:
     - LWorld type system is good for the VM, but has short comings for 
the language
     - ...so let's use something different in the language model, and 
use translation to do the work to keep the VM out of trouble
- Remi: int would have a "ref projection"
- Brian: yes, automatic and total
- Remi: must the VM provide the ref projection ?
- Brian: no the language compiler can provide it,
     - or a migration story might involve some manual specified type
- Remi: ref projections used where
- Brian: circularity, null-ability, compatibility
     - We think you always have a reference projection for inline types
- Brian: figuring out where to put the responsibility
     - how much in javac vs VM ?
- Remi: some playing with eclair model, has empty
- Brian: reference projection can simply be an interface
- Remi: how do we have an "inline record" (abstract record)
- Brian: short answer: "abstract record" become interface
     - ValObj / RefObj are interfaces
     - Interfaces vs abstract:
         - current thinking Interfaces offer few problems (needs more work)

- Remi: does volatile work in the prototype ?
- Simms: nope
- Remi: VarHandle support for "non-volatile" inline
     - Yeah, should throw exception
     - Can we get volatile field decl into the prototype ?
         - Fred: sure, we'll write up a few bug
- Remi:
     - equality "==", shall we make lambda inline class (sentinel problems)
- Brian
     - sure, might be worth looking into, to get people slightly more 
happy with notion equality for lambda
     - Might have some performance implications "fat lambdas", worth 
looking at though


Happy Thanksgiving !