declare function one<T>(handler: (t: T) => void): T
var empty = one(() => {}) // inferred as {}, expected

type Handlers<T> = { [K in keyof T]: (t: T[K]) => void }
declare function on<T>(handlerHash: Handlers<T>): T
var hashOfEmpty = on({
    test: () => {}
})
// inferred as {test(): void}, expected {test: {}}