On Wed, 7 Jul 2021 12:10:16 GMT, Jan Lahoda <jlah...@openjdk.org> wrote:
>> Currently, an enum switch with patterns is desugared in a very non-standard,
>> and potentially slow, way. It would be better to use the standard
>> `typeSwitch` bootstrap to classify the enum constants. The bootstrap needs
>> to accept enum constants as labels in order to allow this. A complication is
>> that if an enum constant is missing, that is not an incompatible change for
>> the switch, and the switch should simply work as if the case for the missing
>> constant didn't exist. So, the proposed solution is to have a new bootstrap
>> `enumSwitch` that accepts `String`s in place of the enum constants, and will
>> internally convert them to the appropriate enum constants, and then it will
>> find the proper case similarly to `typeSwitch`.
>>
>> How does this look?
>
> Jan Lahoda has updated the pull request incrementally with one additional
> commit since the last revision:
>
> If the pattern type is a supertype of the selector type, use selector type
> rather than the pattern type when constructing the bootstrap method
> parameters.
There turned out to be a bug in the patch: considering a switch over enum like:
E e = ...;
switch (e) {
case Object o -> {}
}
(Or, even worse, `case Object o && <guard> ->`), the patch will generate
`Object.class` as a static parameter to the `enumSwitch` bootstrap method. But
the method (rightfully) requires the enum class as the static parameter.
https://github.com/openjdk/jdk17/pull/81/commits/d970402e969d76a017cdfdcbc6556f6d9a9f3bfa
tweaks the code generation to produce `E.class` instead of `Object.class`.
-------------
PR: https://git.openjdk.java.net/jdk17/pull/81
