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Feature: Don't care/anonymous parameter #5586
Description
Many functional languages have a don't care parameter/variable that holds values not used by programs.
For example, a function like Array.prototype.forEach supplies three arguments to the callback. If the code only needs the second argument (index), it will still have to supply a name for the first one. The programmer can use a don't care parameter as the name of the first argument instead. This improves readability and avoids problem of accidentally shadowing.
An additional keyword/comment may have to be introduced to define which string is used for this purpose as the traditional "_" happens to be used by the popular underscore library.
This can also be extended to destructuring code.
Activity
[-]Don't care/anonymous parameter[/-][+]Feature: Don't care/anonymous parameter[/+]RyanCavanaugh commentedon Nov 10, 2015
Just thinking aloud -- would
arr.forEach(( , index) => console.log(index));look too much like a typo?sandersn commentedon Nov 10, 2015
I think so. Also, when commas stack up they get hard to count.
Does the already-supported workaround of
_,__,__, ... suffice?FabianLauer commentedon Nov 10, 2015
I agree with Nathan Shively-Sanders (@sandersn). How about
arr.forEach((void, index) => console.log(index));?Just the first thing that came to mind. Correct me if I'm wrong, but I think this doesn't lead to a conflict with the ES spec as it would be a part of the type system.
coreh commentedon Dec 3, 2015
Maybe
_could be special cased, so that you can use it multiple times, then__and___wouldn't be needed.Would become
LiamGoodacre commentedon Dec 20, 2015
How about
?? For example:(?, x, ?) => x + 1.Given that
_is a valid identifier name, I don't believe it is appropriate to use here.DanielRosenwasser commentedon Dec 20, 2015
You could just use an empty binding pattern like
[]or{}.Since they are not disallowed (see tc39/ecma262#97), I'm inclined to close this unless there's a problem with that workaround.
LiamGoodacre commentedon Dec 20, 2015
Daniel Rosenwasser (@DanielRosenwasser) nice 👍
qc00 commentedon Dec 20, 2015
Daniel Rosenwasser (@DanielRosenwasser) Sounds perfect. Would be nice if this special use case is documented though.
FabianLauer commentedon Dec 21, 2015
Daniel Rosenwasser (@DanielRosenwasser) Great, thanks.