data structure collection traits
```rust
use datastructuretraits::*;
fn useseq<'a, S>(s: &'a mut S) -> usize
where S: SeqMut<'a, usize>,
&'a S: IntoIterator
} else {
s.insert(0, 1);
}
let mut avg = 0;
let len = s.len();
for v in s.into_iter() {
avg += *v;
}
avg / len
}
fn main() {
let mut v: Vec