improve error handling

src/main.rs

@@ -8,6 +8,12 @@ const FILENAME_WIP : &str = "state.wip";
 
 struct LetterCounts([u32; 26]); // tuple
 
+enum DeserializeError {
+    MissingLetter,
+    MissingCount(std::num::ParseIntError),
+    UnexpectedChar,
+}
+
 impl LetterCounts {
     fn add(&mut self, i : usize) {
         self.0[i] += 1;
@@ -32,17 +38,17 @@ impl LetterCounts {
     }
 
     // todo: use serde?
-    fn deserialize(&mut self, s: &str) -> Result<(), Vec<String>> {
+    fn deserialize(&mut self, s: &str) -> Result<(), Vec<DeserializeError>> {
         println!("deserializing...");
 
-        let mut error_strings = Vec::new();
+        let mut error_strings : Vec<DeserializeError> = Vec::new();
         // todo: don't just assume no duplicate (and disagreeing) lines
         for line in s.lines() {
             if let Some((letter, val)) = line.split_once(' ') {
                 let c = match letter.chars().next() {
                     Some(c) => c,
                     None => {
-                        error_strings.push("ERROR: invalid line format, missing character.".to_string());
+                        error_strings.push(DeserializeError::MissingLetter);
                         continue;
                     }
                 };
@@ -51,14 +57,13 @@ impl LetterCounts {
                     let count = match val.parse::<u32>() {
                         Ok(i) => i,
                         Err(e) => {
-                            // todo: don't store strings, unnecessary allocation
-                            error_strings.push(format!("ERROR: invalid line format, missing count. ({})", e));
+                            error_strings.push(DeserializeError::MissingCount(e));
                             continue;
                         }
                     };
                     self.0[index] = count;
                 } else {
-                    error_strings.push("ERROR: encountered non-lowercase alphabetic char".to_string());
+                    error_strings.push(DeserializeError::UnexpectedChar);
                     continue; // we just drop the char/line
                 }
             }
@@ -82,7 +87,14 @@ fn main() {
     // deserialize file contents into data structure
     if let Ok(contents) = fs::read_to_string(FILENAME) {
         if let Err(v) = data.deserialize(&contents) {
-            v.iter().for_each(|s| eprintln!("{}",s));
+            v.iter().for_each(|e| {
+                let e_string = match e {
+                    DeserializeError::MissingLetter => "ERROR: invalid line format, missing character.".to_string(),
+                    DeserializeError::UnexpectedChar => "ERROR: unexpected character".to_string(),
+                    DeserializeError::MissingCount(e) => format!("Error: missing count {}",e),
+                };
+                eprintln!("{}", e_string)
+            });
         }
     } else {
         eprintln!("ERROR: failed to read file");

state.txt

@@ -5,7 +5,7 @@ d 1
 e 2
 f 3
 g 3
-h 3
+h 4
 i 1
 j 0
 k 1