Function intersperse_fold

pub(in ::iter::adapters::intersperse) fn intersperse_fold<I, B, F, G>(iter: I, init: B, f: F, separator: G, started: bool, next_item: Option<I::Item>) -> B
where
    I: Iterator,
    F: FnMut(B, I::Item) -> B,
    G: FnMut() -> I::Item,