# TSR0103: Calling a value of type 'Function' returns 'any'. Give '…' a function type.

> A value of type 'Function' is called, which returns 'any'. Give it a real function type such as '() => unknown'.

## What it means

Calling or constructing a value of type `Function` gives `any`, which would leak into sound code. It's reported at the call.

## Example

```ts
// Calling a value of type Function returns any.
function invoke(fn: Function): unknown {
  return fn(); // @expect TSR0103
}
export const r: unknown = invoke(() => 1);
```

## How to fix

- Give the value a function type: `fn: () => unknown`, or one with the real parameter and return types.
- Use a type parameter if callers pass different function types.

Sound mode is defined in [design record 0007](https://github.com/Webb-Ventures/typescript-rust/blob/main/docs/design/0007-sound-mode.md) (accepted 2026-10-15).

Source: https://ts-r.dev/errors/TSR0103/