Non-binding destructuring assignment

Sebastian McKenzie sebmck at gmail.com
Wed Apr 29 11:43:40 UTC 2015


The binding identifiers are optional. You can do what you want already with:




const lastOfThree = ([,, third]) => {

  return third;

}

On Wed, Apr 29, 2015 at 12:40 PM, Elie Rotenberg <elie at rotenberg.io>
wrote:

> Using array destructuring assignment and constraining linting rules, I
> often find myself having to chose names for bindings I don't intent on
> using. I usually end up using a conventional ignore name, such as _ignore,
> which I "void" to shut up the linter without adding exceptions. Besides the
> linting problem (which can be solved by refining the linting rules), it's
> still a conceptually useless binding.
> Here's a contrived example:
> const lastOfThree = ([first, second, third])  => third;
> Which I usually end up rewriting:
> const lastOfThree = ([_ignore1, _ignore2, third]) => {
>   void _ignore1;
>   void _ignore2;
>   return third;
> }
> This problem doesn't exist when using objects, since only the fields
> specified on the LHS are bound.
> I realize the bigger topic behind non-binding match is refutable pattern
> matching, as per
> http://wiki.ecmascript.org/doku.php?id=strawman:pattern_matching, but being
> able to dismiss a matched (or unmatched) value from a destructuring
> assignment seems a very often desirable feature when programming in a
> functional style (eg. working with lists represented as 2-element arrays).
> Most functional-style languages have a non-binding matching feature.
> This topic has been discussed in the following topics:
> - https://esdiscuss.org/topic/conditional-catch
> - https://esdiscuss.org/notes/2014-07-30
> - https://esdiscuss.org/topic/conditional-catch-clause
> Does anyone else feel the need for a specific means of dismissing a binding
> from a destructuring assignment? Is pattern matching still on discussion?
> Regards,
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