use std::iter::Peekable;
use std::marker::PhantomData;

struct KVIter<'a, T:'a>(PhantomData<&'a T>);
struct MemTableBatchIterator<'a, T:'a>(PhantomData<&'a T>);
struct KeyRef<'a>(PhantomData<&'a ()>);
trait Engine<'b> {}
impl<'a, T: 'a> Iterator for MemTableBatchIterator<'a, T> {
    type Item = ();
    fn next(&mut self) -> Option<()> {
        unimplemented!()
    }
}

fn merge<'b, 'c, E, T>(
    mem_table_iter: &mut Peekable<MemTableBatchIterator<'b, E>>,
    kv_iter: KVIter<'c, T>,
) where
    E: Engine<'b>,
    T: Iterator<Item = KeyRef<'c>>,
{
}

fn main(){
}