Baike.dev
All toolsAI codingTrendingOpen sourceNewsSubmit
Log in
Back to tool/Back to issues
#331·ts-pattern

P.select loses type inference when used with multiple patterns in a single .with

Author: salemkodeCreated Aug 23, 2025Updated Sep 15, 2025

Describe the bug

When using P.select(P.string) with multiple patterns in the same .with clause, the handler parameter is not inferred as string.

Instead, it is inferred as the union of the full object shapes, rather than the selected value.


TypeScript playground with a minimal reproduction case

Playground Link

typescript
import { match, P } from "ts-pattern";

const obj = {} as unknown;

const message = match(obj)
  .with(
    { errors: P.select(P.string) },
    { description: P.select(P.string) },
    (message) => {
      console.log("message", message);
      // ❌ Expected: message is string
      // ❌ Actual: message is inferred as object type
      return `Please enter ${message.replace("length", "characters")}`;
    }
  )
  .otherwise(() => "");

Expected behavior

  • The handler parameter should be inferred as string (from P.select(P.string)), even when multiple patterns are used.

Actual behavior

  • The handler parameter is inferred as the union of the object shapes ({ errors: string } | { description: string }), not the selected string.

Versions

  • TypeScript version: 5.9.2

Source: gvergnaud/ts-pattern

View original on GitHubView discussion on GitHub