🔵 Refactor error result

Author: isaac1024

exercises/tiered_pricing/solutions/isaac1024_baby-steps/src/tiered_pricing.rs

@@ -1,12 +1,25 @@
-fn get_unit_price(number_of_subscriptions: u32) -> Result<u32, String> {
+use std::fmt;
+
+type SubscriptionResult<T> = Result<T, NumberSubscriptionsError>;
+
+#[derive(Debug)]
+struct NumberSubscriptionsError;
+
+impl fmt::Display for NumberSubscriptionsError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Subscriptions must be greater than 0")
+    }
+}
+
+fn get_unit_price(number_of_subscriptions: u32) -> SubscriptionResult<u32> {
     const FIRST_UNIT_PRICE: u32 = 299;
     const SECOND_UNIT_PRICE: u32 = 239;
     const THIRD_UNIT_PRICE: u32 = 219;
     const FOURTH_UNIT_PRICE: u32 = 199;
     const FIFTH_UNIT_PRICE: u32 = 149;
 
     match number_of_subscriptions {
-        0 => Err("Error".to_string()),
+        0 => Err(NumberSubscriptionsError),
         1|2 => Ok(FIRST_UNIT_PRICE),
         3..=10 => Ok(SECOND_UNIT_PRICE),
         11..=25 => Ok(THIRD_UNIT_PRICE),
@@ -15,70 +28,70 @@ fn get_unit_price(number_of_subscriptions: u32) -> Result<u32, String> {
     }
 }
 
-fn get_total_subscription_price(number_of_subscriptions: u32) -> Result<u32, String> {
+fn get_total_subscription_price(number_of_subscriptions: u32) -> SubscriptionResult<u32> {
     Ok(number_of_subscriptions * get_unit_price(number_of_subscriptions)?)
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::tiered_pricing::get_total_subscription_price;
+    use crate::tiered_pricing::{get_total_subscription_price, NumberSubscriptionsError};
 
     #[test]
-    fn when_get_a_subscription_return_299_euros() -> Result<(), String> {
+    fn when_get_a_subscription_return_299_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(299, get_total_subscription_price(1)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_2_subscriptions_return_598_euros() -> Result<(), String> {
+    fn when_get_2_subscriptions_return_598_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(598, get_total_subscription_price(2)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_3_subscriptions_return_717_euros() -> Result<(), String> {
+    fn when_get_3_subscriptions_return_717_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(717, get_total_subscription_price(3)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_10_subscriptions_return_2390_euros() -> Result<(), String> {
+    fn when_get_10_subscriptions_return_2390_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(2390, get_total_subscription_price(10)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_11_subscriptions_return_2409_euros() -> Result<(), String> {
+    fn when_get_11_subscriptions_return_2409_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(2409, get_total_subscription_price(11)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_25_subscriptions_return_5475_euros() -> Result<(), String> {
+    fn when_get_25_subscriptions_return_5475_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(5475, get_total_subscription_price(25)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_26_subscriptions_return_5174_euros() -> Result<(), String> {
+    fn when_get_26_subscriptions_return_5174_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(5174, get_total_subscription_price(26)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_50_subscriptions_return_9950_euros() -> Result<(), String> {
+    fn when_get_50_subscriptions_return_9950_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(9950, get_total_subscription_price(50)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_51_subscriptions_return_7599_euros() -> Result<(), String> {
+    fn when_get_51_subscriptions_return_7599_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(7599, get_total_subscription_price(51)?);
         Ok(())
     }
 
     #[test]
-    fn when_get_52_subscriptions_return_7748_euros() -> Result<(), String> {
+    fn when_get_52_subscriptions_return_7748_euros() -> Result<(), NumberSubscriptionsError> {
         assert_eq!(7748, get_total_subscription_price(52)?);
         Ok(())
     }