Rust template template parameter

main.rs

use std::collections::*;
use std::hash::Hash;
use std::iter::FromIterator;


trait SetFunc<T> { 
    type Set: IntoIterator + FromIterator<T>;
}

struct BTreeSetF;

impl<T: Ord + Eq> SetFunc<T> for BTreeSetF {
    type Set = BTreeSet<T>;
}

struct HashSetF;

impl<T: Eq + Hash> SetFunc<T> for HashSetF {
    type Set = HashSet<T>;
}


fn uni<Set: SetFunc<T> + SetFunc<(T,T)>, T: Copy>(input: &[T]) -> usize {
    input.iter().copied().collect::
        < <Set as SetFunc<T>>::Set >
    ().into_iter().count() *
    
    input.windows(2).map(|a|(a[0], a[1])).collect::
        < <Set as SetFunc<(T,T)>>::Set >
    ().into_iter().count()
}

fn main() {
    println!("{}", uni::<BTreeSetF, _>(&[1,2,3,3,2,3]));
    println!("{}", uni::<HashSetF, _>(&[1,2,3,3,2,3]));
}