Attribute Macro illicit::from_env

#[from_env]

Defines required illicit::get values for a function. Binds the provided types as if references to them were implicit function arguments:

#[derive(Debug, PartialEq)]
enum TextDirection {
    Ltr,
    Rtl,
}

impl TextDirection {
    fn set<R>(self, op: impl FnOnce() -> R) -> R {
        illicit::Layer::new().offer(self).enter(op)
    }
}

#[illicit::from_env(direction: &TextDirection)]
fn align_text_to_end(t: &str, width: usize) -> String {
    assert!(t.len() <= width, "no linebreaking included, this is unicode-sinful as it is");
    match direction {
        TextDirection::Ltr => format!("{0:>1$}", t, width),
        TextDirection::Rtl => format!("{0:<1$}", t, width),
    }
}

let get_aligned = || align_text_to_end("whoa", 8);

let right_aligned = TextDirection::Ltr.set(get_aligned);
let left_aligned = TextDirection::Rtl.set(get_aligned);

assert_eq!(right_aligned, "    whoa");
assert_eq!(left_aligned, "whoa    ");

Panics

Will cause the annotated function to panic if it is invoked without the requested type in its environment:

align_text_to_end("oopsie", 8);

This attribute adds an Environment Expectations section to the doc comments of the annotated function to communicate this risk to users.