use str_match::str_match;

fn f(a: &str) -> &str {
    str_match! {
        match a {
            "abc{x}ghi" => x,
            "aaa{x}" => x,
            "{{{x}}}" => x,
            _ => "!",
        }
    }
}

fn main() {
    assert_eq!(f("abcdefghi"), "def");
    assert_eq!(f("aaabbbccc"), "bbbccc");
    assert_eq!(f("{000}"), "000");
    assert_eq!(f("xyz"), "!");
}