Function itertools::minmax::minmax_impl

pub fn minmax_impl<I, K, F, L>(
    it: I,
    key_for: F,
    lt: L
) -> MinMaxResult<I::Item>where
    I: Iterator,
    F: FnMut(&I::Item) -> K,
    L: FnMut(&I::Item, &I::Item, &K, &K) -> bool,

Implementation guts for minmax and minmax_by_key.