Help with type narrowing

[sterile lark]

In this snippet, I've tried to get the type of the Composed typed object narrowed, as per the prop passed to the kind key, but it seems to simply clump every property of Something together. Is there a way to infer this?

[astral lake]

@sterile lark Here's a shortened URL of your playground link! You can remove the full link from your message.

_lofty.dev#0

Playground Link

Preview:```ts
type Union = "a" | "b" | "c" | "d" | "e";
type Something<T extends Union> = T extends "a" ? { f: string } : { g: string };
type Composed<T> = Something<T> & { kind: T }

const config = {
s: { kind: "a", }
} as const satisfies Record<string, Composed<Union>>;```

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[grave ivy]

uh, just add the extends Union constraint to Composed?

this is a discriminated union btw

!hb disc

[astral lake]

Get Started / TypeScript for Functional Programmers

Discriminated Unions

[sterile lark]

Adding that doesn't seem to effect the intellisense offered when writing config, though.. which's the problem

[grave ivy]

not sure what you mean by that?

do you want only f to show up there?

[sterile lark]

What I wanted was the type to be narrowed based on what I passed to T itself..
if I passed kind: "a", yes, I want only f to show up

[astral lake]

that_guy977#0

Playground Link

Preview:```ts
type Union = "a" | "b" | "c" | "d" | "e";
type Something<T extends Union> = T extends "a" ? { f: string } : { g: string };
type Composed<T extends Union> = T extends T ? Something<T> & { kind: T } : never

const config = {
s: { kind: "a", }
} as const satisfies Record<string, Composed<Union>>;```

You can choose specific lines to embed by selecting them before copying the link.

[sterile lark]

Well.. that's something...

Ah, I see, that's clever, thank you