Generic scalar product in Rust

scalar.rs

use std::default::Default;
use std::ops::{Add, Mul};

fn scalar<T: Add<Output = T> + Default>(a: &[T], b: &[T]) -> T
    where for<'a> T: Mul<&'a T, Output = T>,
          for<'a, 'b> &'a T: Mul<&'b T, Output = T>
{
    assert_eq!(a.len(), b.len());
    a.iter()
        .zip(b.iter())
        .map(|x| x.0 * x.1)
        .fold(Default::default(), |acc, x| acc + x)
}

fn main()
{
    let a = [3.0, 2.0, -1.5, 1.0];
    let b = [1.0, 2.0, 3.0, -2.5];
    println!("{}", scalar(&a, &b));
}