JEP 302: Underscore as enhanced for loop parameter?

Brian Goetz brian.goetz at
Thu Oct 5 23:10:03 UTC 2017

Yes, seems reasonable.

On 10/5/2017 1:21 AM, Tagir Valeev wrote:
> Hello!
> I think underscore could be allowed as an enhanced for parameter. In
> rare cases it's necessary to iterate over Iterable without using the
> elements like here:
> long countElements(Iterable<?> iterable) {
>    long count = 0;
>    for(Object _ : iterable) count++;
>    return count;
> }
> Here we have a place where we're syntactically forced to declare a
> variable, but we don't need one. Similarly to a catch block this
> perfectly fits the underscore use cases. This would also help to
> perform code static analysis. It's common for IDEs to warn if a loop
> variable is unused (which could be a bug like another variable is used
> instead by mistake). Using underscore we explicitly say that we don't
> need a variable here. In IntelliJ IDEA we suggest using an "ignored"
> name in such case, but it's still a valid name and can be used
> accidentally or clashed with another name.
> Sorry if this was already discussed, I wasn't able to find any public
> discussions on this topic.
> With best regards,
> Tagir Valeev.

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