Function merge_iters 

pub fn merge_iters<'a, 'b, A: Iterator<Item = (&'a Key, &'a Value)>, B: Iterator<Item = (&'b Key, &'b Value)>>(
    a: A,
    b: B,
) -> MergeIter<'a, 'b, A, B> 

Available on crate feature metrics only.

Merge two iterators, yielding sorted results