How to explicitly pass type arguments to generic functions in flow?

Question

I'm trying to explicitly specify the type when calling a generic function.

For example:

export function gen<T>(a: string): { eat: T => string } {
  return {
    eat: (v: T): string => a
  };
}

Of course, using C++-like syntax doesn't work, because flow extends Javascript syntax, and this is already a valid JS expression (a comparison):

const { eat } = gen<number>("str")

What is the correct syntax?

I want to pass a type explicitly, because otherwise this sort of code won't produce an error:

const { eat } = gen("str")
const a = eat(5)
// I want this to be an error, but it is not
const b = eat("foo")

I can of course annotate the assignment, causing the desired generic type to be inferred, but that can be cumbersome. Try it here

Answer 1

It is able since v0.72. CHANGELOG. Example

// @flow

declare function makeFoo<T>(): T;

const t = makeFoo<number>();

(t: number);

// $ExpectError
(t: string);