interface IOne { (j: string): number; }
    interface ITwo { (j: number): number; }
    function dualArg(i: string, process: IOne | ITwo): number {
        // something like this
        if (process instanceof ITwo) {
            // call with numeric arg
            return process(i);
        } else {
            // conver to number
            return process(+i);
        }
    }
    function inc(i: number): number {
        return ++i;
    }
    function idem(text: string): number {
        return +text;
    }
    it('determine function signature', () => {
        expect(dualArg('1', inc)).toBe(2);
        expect(dualArg('1', idem)).toBe(1);
    })