const check =<T extends object | null, Ret, Args extends [...string[], T]>(settings:{load:(...args:Args)=>Ret, save:(internal:Ret)=>Args})=>
{
    return {} as [never, ...Args][Args["length"]];
}

function load(a1:string, a2:string, a3:string, a4:Record<string, number>)
{
    return [1, 2, 3]
}

type LoadArgs = Parameters<typeof load>;

function save(n:number[])
{
    return ["a", "b", "c", { x: 1, y: 2 }] as LoadArgs
}

const c1 = check({load, save});