You can provide internals of a module via pub use

src/lib.rs

@@ -1,128 +1,4 @@
-use std::ops::{Add, Div, Mul, Sub};
+mod geometry;
+mod math;
 
-#[derive(Copy, Clone)]
+pub use math::Point3;
-pub struct Vector3 {
-    x: f64,
-    y: f64,
-    z: f64,
-}
-
-impl Vector3 {
-    pub fn new(x: f64, y: f64, z: f64) -> Vector3 {
-        Vector3 { x, y, z }
-    }
-}
-
-impl Add for Vector3 {
-    type Output = Vector3;
-
-    fn add(self, rhs: Vector3) -> Self::Output {
-        Vector3::new(self.x + rhs.x, self.y + rhs.y, self.z + rhs.z)
-    }
-}
-
-impl Sub for Vector3 {
-    type Output = Vector3;
-
-    fn sub(self, rhs: Vector3) -> Self::Output {
-        Vector3::new(self.x - rhs.x, self.y - rhs.y, self.z - rhs.z)
-    }
-}
-
-impl Mul<f64> for Vector3 {
-    type Output = Vector3;
-
-    fn mul(self, rhs: f64) -> Self::Output {
-        Vector3::new(self.x * rhs, self.y * rhs, self.z * rhs)
-    }
-}
-
-impl Mul<Vector3> for f64 {
-    type Output = Vector3;
-
-    fn mul(self, rhs: Vector3) -> Self::Output {
-        Vector3::new(self * rhs.x, self * rhs.y, self * rhs.z)
-    }
-}
-
-impl Mul for Vector3 {
-    type Output = f64;
-
-    fn mul(self, rhs: Vector3) -> Self::Output {
-        self.x * rhs.x + self.y * rhs.y + self.z * rhs.z
-    }
-}
-
-impl Div<f64> for Vector3 {
-    type Output = Vector3;
-
-    fn div(self, rhs: f64) -> Self::Output {
-        Vector3::new(self.x / rhs, self.y / rhs, self.z / rhs)
-    }
-}
-
-#[derive(Copy, Clone)]
-pub struct Point3 {
-    x: f64,
-    y: f64,
-    z: f64,
-}
-
-impl Point3 {
-    pub fn new(x: f64, y: f64, z: f64) -> Point3 {
-        Point3 { x, y, z }
-    }
-
-    pub fn get_x(&self) -> f64 {
-        self.x
-    }
-}
-
-impl Add<Vector3> for Point3 {
-    type Output = Point3;
-
-    fn add(self, rhs: Vector3) -> Self::Output {
-        Point3::new(self.x + rhs.x, self.y + rhs.y, self.z + rhs.z)
-    }
-}
-
-impl Sub for Point3 {
-    type Output = Vector3;
-
-    fn sub(self, rhs: Point3) -> Self::Output {
-        Vector3::new(self.x - rhs.x, self.y - rhs.y, self.z - rhs.z)
-    }
-}
-
-pub struct Plane {
-    point: Point3,
-    normal: Vector3,
-}
-
-impl Plane {
-    pub fn new(point: Point3, normal: Vector3) -> Plane {
-        Plane { point, normal }
-    }
-}
-
-pub struct Line {
-    point: Point3,
-    direction: Vector3,
-}
-
-pub struct Sphere {
-    point: Point3,
-    radius: f64,
-}
-
-impl Sphere {
-    pub fn new(point: Point3, radius: f64) -> Sphere {
-        Sphere { point, radius }
-    }
-}
-
-pub enum Geometry {
-    Sphere(Sphere),
-    Plane(Plane),
-    Line(Line),
-}

src/main.rs

@@ -1,4 +1,4 @@
-use hello::*;
+use hello::Point3;
 
 fn main() {
     let p = Point3::new(0.0, 0.0, 0.0);