addition: Fraction Error, Fraction and constructor

src/lib.rs

@@ -1,14 +1,38 @@
-pub fn add(left: u64, right: u64) -> u64 {
-    left + right
+pub struct Fraction {
+    num: i64,
+    den: i64,
+}
+
+#[derive(Debug)]
+pub enum FractionError {
+    DivisionByZero,
+    ZeroDenominator,
+    Overflow,
+}
+
+impl std::fmt::Display for FractionError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            FractionError::DivisionByZero => write!(f, "Division by zero"),
+            FractionError::ZeroDenominator => write!(f, "Denominator can't be zero"),
+            FractionError::Overflow => write!(f, "Numeric overflow"),
+        }
+    }
+}
+
+impl std::error::Error for FractionError {}
+
+impl Fraction {
+    pub fn new(num: i64, den: i64) -> Result<Self, FractionError> {
+        if den == 0 {
+            return Err(FractionError::ZeroDenominator);
+        }
+
+        Ok(Fraction { num, den })
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
-
-    #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
-    }
 }