extern crate nalgebra as na;

use na::{Unit, Vector3};

fn length_on_direction_with_unit(v: &Vector3<f32>, dir: &Unit<Vector3<f32>>) -> f32 {
  // No need to normalize `dir`: we know that it is non-zero and normalized.
  v.dot(dir.as_ref())
}



fn length_on_direction_without_unit(v: &Vector3<f32>, dir: &Vector3<f32>) -> f32 {
  // Obligatory normalization of the direction vector (and test, for robustness).
  if let Some(unit_dir) = dir.try_normalize(1.0e-6) {
    v.dot(&unit_dir)
  }
  else {
    // Normalization failed because the norm was too small.
    panic!("Invalid input direction.")
  }
}

fn main() {
    let v = Vector3::new(1.0, 2.0, 3.0);

    let l1 = length_on_direction_with_unit(&v, &Vector3::y_axis());
    let l2 = length_on_direction_without_unit(&v, &Vector3::y());

    assert_eq!(l1, l2)
}