examples/rust_example/hello_world/foo/src/lib.rs

#[derive(Debug)]
pub struct Foo {
    s: &'static str,
    i: &'static str
}

impl Foo {
    pub fn new(s: &'static str) -> Foo {
        Foo{s: s, i: "foo"}
    }
}

#[no_mangle]
pub extern "C" fn call_from_c() -> i32 {
    42
}