Why return type is not inferred?

The generic return type R should be inferred as string, but it’s instead unknown. Why and how to make it to be inferred correctly?

function call<Args extends any[], R, F extends ((...args: Args) => R)>(
  fn: F, ...args: Args
): R {
  return fn(...args)
}

function some<T>(a: T[]): string { return "" }

let v = call(some, [1]) // => inferred type of v is unknown

>Solution :

Use ReturnType<F> as the return type of your function to infer the type from the passed function instead of using the R generic

function call<Args extends any[], F extends ((...args: Args) => any)>(
  fn: F, ...args: Args
): ReturnType<F> {
  return fn(...args)
}

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