Evolving the wrapper classes

[Dan Smith]

> On Jun 19, 2020, at 11:07 AM, Tobi Ajila <Tobi_Ajila at ca.ibm.com> wrote:
> 
> I am still a little unclear as to what the motivation is for this. Is this solely for specialized generics?
> 
> In Dan's examples with `I` and `java/lang/Integer$val`, the only places where conversions are needed are when primitives are used as type parameters or to call instance methods on them, both of which can already be done with primitive arrays. So in the LW3 - LW20 timeframe would we have any need for these conversions? If so, could you provide some examples?

I think it comes down to specialization and subtyping.

Pre-specialization, here's one example that uses subtyping:

int[] arr = { 1 };
Object[] objs = arr; // just like Point[] <: Object[]
Object obj = objs[0];
Integer i = (Integer) obj;

This would compile to something like:

iconst_1
newarray T_INT
dup
iconst_0
iconst_1
iastore
astore_0

aload_0
astore_1

aload_1
iconst_0
aaload
astore_2

aload_2
checkcast java/lang/Integer
astore_3

Going in the other direction—allocating a [Qjava/lang/Integer; and then using iaload/iastore on it—may not be necessary unless/until the language supports "new T[]" in specialized code, but it tentatively makes sense to support now anyway, rather than having to come back and fix it up later.

> In the case of specialized generics, is the intention that `[I` (and I suppose `I` as well) will appear in generic code?

If you mean "can '[<T>' be specialized to '[I'?", the answer is no. The primitive types cannot act as type arguments.