From 24c91a4a0b987a6889f6803e5390b79c4762418b Mon Sep 17 00:00:00 2001
From: Alexander Launi <alex.launi@gmail.com>
Date: Sat, 21 Mar 2020 17:20:03 -0400
Subject: [PATCH] Implement factorial using generic mathematics

---
 03_recursion/rust/03_factorial/Cargo.toml  |  1 +
 03_recursion/rust/03_factorial/src/main.rs | 16 ++++++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/03_recursion/rust/03_factorial/Cargo.toml b/03_recursion/rust/03_factorial/Cargo.toml
index cec2d7e..223a6ec 100644
--- a/03_recursion/rust/03_factorial/Cargo.toml
+++ b/03_recursion/rust/03_factorial/Cargo.toml
@@ -7,3 +7,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+num-traits = "0.2"
diff --git a/03_recursion/rust/03_factorial/src/main.rs b/03_recursion/rust/03_factorial/src/main.rs
index b9c7425..5ebd5b2 100644
--- a/03_recursion/rust/03_factorial/src/main.rs
+++ b/03_recursion/rust/03_factorial/src/main.rs
@@ -1,9 +1,17 @@
-fn fact(x: u32) -> u32 {
-    if x == 1 {
-        return 1;
+use std::ops::Sub;
+use std::fmt::Display;
+use num_traits::identities::One;
+
+fn fact<T: PartialOrd + PartialEq + One + Sub<Output = T> + Copy + Display>(x: T) -> T {
+    if x < T::one() {
+        panic!("Invalid number: {}", x);
     }
 
-    return x * fact(x - 1);
+    if x.is_one() {
+        return T::one();
+    }
+
+    return x * fact(x - T::one());
 }
 
 fn main() {