Create reusable line reader

2021/src/common.rs

@@ -4,6 +4,33 @@ use std::io::Read;
 use std::marker::PhantomData;
 use std::str::FromStr;
 
+pub struct LineIter<'a> {
+    reader: BufReader<&'a mut dyn Read>,
+    buffer: String,
+}
+
+impl<'a> LineIter<'a> {
+    pub fn new(input: &'a mut dyn Read) -> Self {
+        Self {
+            reader: BufReader::new(input),
+            buffer: String::new(),
+        }
+    }
+
+    /// Get the next line, or None
+    ///
+    /// This is deliberately not an [Iterator] impl as those cannot hand out references to self.
+    pub fn next(&mut self) -> Option<&str> {
+        self.buffer.clear();
+
+        if matches!(self.reader.read_line(&mut self.buffer), Ok(n) if n > 0) {
+            Some(self.buffer.trim_end_matches('\n'))
+        } else {
+            None
+        }
+    }
+}
+
 /// Line-based iterator/parser
 ///
 /// For each line of the input, attempt to parse it as the requested type. Iteration is stopped on
@@ -13,33 +40,23 @@ pub struct LineParser<'a, I>
 where
     I: FromStr,
 {
-    reader: BufReader<&'a mut dyn Read>,
-    buffer: String,
+    iter: LineIter<'a>,
     _data: PhantomData<I>,
 }
 
 impl<'a, I: FromStr> LineParser<'a, I> {
     pub fn new(input: &'a mut dyn Read) -> Self {
         Self {
-            reader: BufReader::new(input),
-            buffer: String::new(),
+            iter: LineIter::new(input),
             _data: PhantomData,
         }
     }
-
-    fn next_line(&mut self) -> Option<&str> {
-        self.buffer.clear();
-
-        self.reader.read_line(&mut self.buffer).ok()?;
-
-        Some(self.buffer.trim())
-    }
 }
 
 impl<'a, I: FromStr> Iterator for LineParser<'a, I> {
     type Item = I;
 
     fn next(&mut self) -> Option<Self::Item> {
-        self.next_line()?.parse().ok()
+        self.iter.next()?.parse().ok()
     }
 }