use std::marker::PhantomData;

trait NewIterator {
    type Item;
    fn next(&mut self) -> Option<Self::Item>;
}
fn map<I,F,T,R>(i:I, f:F)
    -> impl NewIterator<Item=R>
    where I: NewIterator<Item=T>,
          F: FnMut(T) -> R
{
    struct Map<I,F,R>{ i:I, f:F, p:PhantomData<R> };
    impl<I,F,T,R> NewIterator for Map<I,F,R>
        where I: NewIterator<Item=T>,
              F: FnMut(T) -> R
    {
        type Item = R;
        fn next(&mut self) -> Option<R> {
            match self.i.next() {
                Some(t) => Some((self.f)(t)),
                None => None
            }
        }
    }
    Map{i:i, f:f, p:PhantomData}
}


fn main(){

}