microsoft / microsoft/TypeScript

support match for type infer

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Description

Search Terms

Suggestion

As a suggestion, there is any plans to support match keyword in type inference to simplify the type destruction and T extends P test and make code more expressive.
Support match in type inference.

Use Cases

type Infer<T> = match T {
  { prop: infer P } => P
  [infer P] => P
  _ => never // default
}

The above is equal to:

type Infer<T> = T extends { prop: infer P }
  ? P
  : T extends [infer P]
    ? P
    : never

## Checklist

My suggestion meets these guidelines:

* [x] This wouldn't be a breaking change in existing TypeScript/JavaScript code
* [x] This wouldn't change the runtime behavior of existing JavaScript code
* [x] This could be implemented without emitting different JS based on the types of the expressions
* [x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
* [x] This feature would agree with the rest of [TypeScript's Design Goals](https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals).

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

The issue names no files, tests, or entry points. Start by comparing the proposed match-based type inference with the conditional-type examples in the description; done means the syntax, inference behavior, and default case have an agreed design and corresponding implementation plan.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
25/100

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