RFR: 8188055: (ref) Add Reference::refersTo predicate [v6]

[Daniel Fuchs]

On Wed, 28 Oct 2020 08:54:31 GMT, Peter Levart <plevart at openjdk.org> wrote:

>> Some thoughts regarding the parameter type of refersTo. Summary: I think `refersTo(T)` is fine and that we don't want to change it to `refersTo(Object)`.
>> 
>> I don't think we have a migration issue similar to generifying collections, where there was a possibility of changing `contains(Object)` to `contains(E)`. If that had been done, it would have been a source compatibility issue, because changing the signature of the method potentially affects existing code that calls the method. That doesn't apply here because we're adding a new method.
>> 
>> The question now falls to whether it's preferable to have more convenience with `refersTo(Object)` or more type-safety with `refersTo(T)`. With the generic collections issue, the migration issue probably drove the decision to keep `contains(Object)`, but this has resulted in a continual set of complaints about the lack of an error when code passes an instance of the "wrong" type. I think that kind of error is likely to occur with `refersTo`. Since we don't have a source compatibility issue here, we can choose the safer API and avoid this kind of problem entirely.
>> 
>> The safer API does raise the possibility of having to add inconvenient unchecked casts and local variables in certain places, but I think Mandy's comment about the code already having a reference of the "right" type is correct. Her prototype webrev linked above shows that having to add unchecked casts is fairly infrequent.
>
>> Some thoughts regarding the parameter type of refersTo. Summary: I think `refersTo(T)` is fine and that we don't want to change it to `refersTo(Object)`.
>> 
> I agree that we don't have a migration problem here that collections had. So let it be `refersTo(T)` then.

I agree as well.

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PR: https://git.openjdk.java.net/jdk/pull/498