On Tue, 22 Jun 2021 19:41:55 GMT, Jan Lahoda <[email protected]> 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
>> `enumConstant` that converts the enum constant name to the enum constant,
>> returning `null`, if the constant does not exist. It delegates to
>> `ConstantBootstraps.enumConstant` to do the actual conversion. And
>> `typeSwitch` accepts `null`s as padding.
>>
>> How does this look?
>
> Jan Lahoda has updated the pull request incrementally with one additional
> commit since the last revision:
>
> Updating javadoc, as suggested.
src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java line 175:
> 173: * Bootstrap method for linking an {@code invokedynamic} call site
> that
> 174: * implements a {@code switch} on a target of an enum type. The
> static
> 175: * arguments are used to encode the case labels associated to the
> switch
`String` and `Class` should appear in code blocks perhaps, or link tags? Also,
I think this text could be improved by splitting the sentence by using a bullet
list:
The static arguments are used to encode the case labels associated to the switch
construct, where each label can be encoded in two ways:
* as a String value, which represents the name of the enum constant associated
with the label
* as a Class value, which represents the enum type associated with a type test
pattern
src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java line 218:
> 216: * {@code Class} of the target enum type.
> 217: * @throws Throwable if there is any error linking the call site
> 218: * @jvms 4.4.6 The CONSTANT_NameAndType_info Structure
Not sure what we do for other bootstraps, but I wonder if the throws clause
here should be more specific - for instance the LambdaMetafactory tells when an
exception is gonna be triggered. Here it seems like there are a couple of cases
which can be called out, where we know that linkage is going to fail.
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PR: https://git.openjdk.java.net/jdk17/pull/81
