# Extract

`import { Extract } from "destack:types";`

Keep union members of `T` assignable to `U`.

```ds title="Extract"
export type Extract<T, U> = T extends U ? T : never
```

[language/library/src/types/object.ds:48](https://github.com/destack-sh/destack/blob/main/language/library/src/types/object.ds#L48)