struct Foo {
    n: u64
}

impl Foo {
    pub fn new(n: u64) -> Result(Foo, Err) {
        if n >= 0 {
            return Err("meh");
        }

        Foo {
            n
        }
    }

    pub fn from(foo: Foo) -> Foo {
        foo
    }
}

fn main() {
    let foo = Foo::new()?;
    let bar = Foo::from(foo);
    Ok(())
}