Updated State of the Specialization

Simon Ochsenreither simon at ochsenreither.de
Sun Dec 21 15:14:03 UTC 2014


> Which is exactly what the Map.get example in the document proposes; 
> migrate the API to a better place, while retaining migration 
> compatibility with the billions of lines of outstanding code.
On this we agree.

> But it needs some language help to retain compatibility.
That's the thing I'm skeptic about.

> I think this may be the actual point of contention here; it seems 
> you're willing to inflict incompatibility on the user base for the 
> sake of progress.
Absolutely not! Everything I suggest is intended to be compatible.

I think the point of contention is that the draft proposes a really 
complicated way to "disable" inconvenient methods like Map#get for value 
types, and I don't believe that
   a) it is absolutely necessary to disable those methods and
   b) the complexity is worth it to achieve this goal.

If we start doctoring Map#get and List#remove, what does this draft have 
in store for java.util.Date and java.util.Calendar?

My earlier suggestion to just keep inconvenient methods around is even 
_more_ compatible for people doing the migration, than selectively 
disabling such methods.

If you want to steer people away from those methods, add a 
@DeprecatedForValueTypes annotation, let the compiler emit a warning and 
be done.

> We've not yet settled on whether user-defined value types can define 
> their own default value,
How will this work if you have e. g. an Array of value-type T ... will 
you go through the whole array and initialize it to the default value 
after allocation? Or require extra bits to track which elements have 
been initialized already?

> or whether they just get "all fields initialized to their default 
> value".  The latter is certainly simpler, but either way, there's a 
> path to specializing the aconst_null to this (e.g., invoke no-arg 
> "constructor".)
So there are 3+ different ways to do it now? Depending on whether you 
are in specialized or erased code and whether you have references, 
primitives or value types?


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