Draft JEP: Unnamed local variables and patterns

[Till Brychcy]

> 7. a resource specification of a try-with-resources statement
> 
> Today we get this warning with a TWR-statement if the local is ignored:
> 
> >
>  javac -Xlint:all MyScopedLock.java
> 
> MyScopedLock.java:23: warning: [try] auto-closeable resource ignored is never referenced in body of corresponding try statement
>         try(MyScopedLock ignored = l.lock()) {
>                          ^
> 1 warning
> 
> So here we may have a clash of philosophies for the enhanced-for and how people
> use the `AutoCloseable`.


We have a similar use case: a logging framework that uses the close() call to measure the runtime of some code block.

It looks like this:

try (__ __ = ThreadLogger.block(SomeClass.class, "someAction")) {
     // some code
}

Note we named the helper class and variable already "__" to make clear that they are not used - before Java 8 we used to called them "_“  :-)

Big advantages in comparison to e.g. a lambda based solution are that this doesn’t interfere with exceptions and variables outside the try statement can be assigned.

There are also more cases reported by other people in https://bugs.eclipse.org/bugs/show_bug.cgi?id=560733 , which why an already implemented warning for such variables by Eclipse was removed again.


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