use std::borrow::Borrow;

struct ObjType;

struct Client<'a> {
    Obj: &'a mut ObjType,
}

struct Sender;

trait Handler{}
impl<'a> Handler for Client<'a> {}

fn connect_once<U, F, H>(url: U, factory: F) -> Result<(),()>
where
    U: Borrow<str>,
    F: FnOnce(Sender) -> H,
    H: Handler,
{
    Ok(())
}

fn connect<U, F, H>(url: U, factory: F) -> Result<(),()>
where
    U: Borrow<str>,
    F: FnMut(Sender) -> H,
    H: Handler,
{
    Ok(())
}

fn main() {
    let mut obj = ObjType;
    //connect("", |_:Sender| Client{Obj:&mut obj});//cannot infer an appropriate lifetime
    connect_once("", |_:Sender| Client{Obj:&mut obj});
}