Function expect 

pub fn expect<E>() -> impl Deref<Target = E> + 'static
where
    E: Any + Debug + 'static,

Returns a reference to a value in the current environment, as get does, but panics if the value has not been set.

The panic message includes the stack of current Layers and their contents.

Examples

let msg = "hello!";
illicit::Layer::new().offer(String::from(msg)).enter(|| {
    assert_eq!(&*illicit::expect::<String>(), msg);
});

Panics if the requested type is not in the environment:

println!("{}", &*illicit::expect::<String>());