struct Schema<F>
where
    F: Fn() -> String
{
    f: F,
}

impl<F> Schema<F>
where
    F: Fn() -> String
{
    fn new(f: F) -> Self {
        Schema { f }
    }

    fn test(&self) {
        println!("{}", (self.f)())
    }
}

fn test() -> String {
    "test string".to_string()
}

fn range(r: std::ops::Range<usize>) -> impl Fn() -> String {
    move || -> String { format!("range() min:{} max:{}", r.start, r.end) }
}

fn main() {
    let schema = Schema::new(test);
    schema.test();

    let schema = Schema::new(range(1 .. 65000));
    schema.test();
}