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unused-params

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Inactive
Classification: Syntactic Change
Human Validated: KW
Title: Unused Function Parameters
Authors: Gus Caplan
[Rejected][unused-params-notes]: the need to solve the problem does not outweigh the hazards
Last Presented: None
Stage Upgrades:
Stage 1: NA Stage 2: NA
Stage 2.7: NA
Stage 3: NA
Stage 4: NA
Last Commit: 2020-08-12
Topics: functions others objects
Keywords: lambda placeholder destructuring
GitHub Link: https://github.com/devsnek/proposal-unused-function-parameters
GitHub Note Link: https://github.com/tc39/notes/blob/HEAD/meetings/2020-09/sept-24.md#unused-function-parameters-for-stage-1

Proposal Description:

Unused Function Parameters

The Problem

doSomething((unused1, unused2, somethingUseful) => {
  doSomethingWith(somethingUseful);
});
 
doSomething((_, __, somethingUseful) => {
  doSomethingWith(somethingUseful);
});

Solutions

Elisions

doSomething(( , , somethingUseful) => {
  doSomethingWith(somethingUseful);
});
  • Matches with existing destructuring
    • ([, c]) is already valid
  • Some might say it looks weird

Placeholder Syntax

doSomething((?, ?, somethingUseful) => {
  doSomethingWith(somethingUseful);
});
 
doSomething((*, *, somethingUseful) => {
  doSomethingWith(somethingUseful);
});
 
// etc.
  • Most explicit, clearly “using up” a parameter without binding it
  • Requires more syntax

Placeholder Identifier

doSomething((_, _, somethingUseful) => {
  doSomethingWith(somethingUseful);
});
 
doSomething((_, _, somethingUseful) => {
  print(_); // IdentifierReference : `_` early error?
  doSomethingWith(somethingUseful);
});
  • Arguably most natural, other languages use this (C#, Rust, etc.)
  • Any valid identifiers are already valid identifiers, could conflict with existing code

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