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Named Generic Type Parameter #26834

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@KSXGitHub

Description

@KSXGitHub

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Suggestion

Allow generic consumer to pass generic argument by name, for instance:

interface Provider<Foo, Bar, Baz, Qux, Quux, ...> {
  foo: Foo
  bar: Bar
  tup: [Baz, Qux, Quux]
  ...
}

type Consumer = Provider<
  Foo = number,
  Bar = string,
  ...
>

let consumer: Provider<
  Foo = {},
  Bar = [],
  ...
>

This would allow us to write and use a generic with thousands of parameter without decreasing readability.

NOTES

  • Before you ask, this feature request is not a duplicate of Proposal: allow type arguments of generic being named #22631 in any shape or form.
  • This is similar to keyword (named) arguments in Python.
    • Vanilla JavaScript doesn't need keyword arguments as it already has objects, but there's no equivalent for TypeScript generic arguments.

Use Cases

Above

Examples

Above

Checklist

My suggestion meets these guidelines:

  • This wouldn't be a breaking change in existing TypeScript / JavaScript code
  • This wouldn't change the runtime behavior of existing JavaScript code
  • This could be implemented without emitting different JS based on the types of the expressions
  • This isn't a runtime feature (e.g. new expression-level syntax)

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