#[derive(Default, Debug)]
struct SrcStruct { key_src: i32 }
#[derive(Default, Debug)]
struct DestStruct { key_dst: i32 }

impl Iterator for DestStruct {
    type Item = i32;
    fn next(&mut self) -> Option<Self::Item> {
        Some(self.key_dst)
    }
}

fn mapper<'a, I>(src: I) -> impl Iterator<Item = DestStruct>
where
    I: IntoIterator<Item = &'a SrcStruct>,
{
    let objs = src
        .into_iter()
        .map(|val|{
            DestStruct { key_dst: val.key_src + 10 }
        });
    objs
}

fn main() {
    let src = vec![
        &SrcStruct{key_src: 1},
        &SrcStruct{key_src: 2},
        &SrcStruct{key_src: 3},
    ];
    let dst = mapper(src);
    for i in dst {
        println!("dst: {:?}", i.key_dst);
    }
}