Macro cookie_factory::gen_many_ref

macro_rules! gen_many_ref {
    (($i:expr, $idx:expr), $l:expr, $f:expr) => { ... };
}

gen_many_ref!(I, Iterable<V>, Fn(I,V)) => I -> Result<I,E> Applies the generator $f to every element of $l, passing arguments by reference.