Clean up day 13 a little.

2021/src/common.rs

@@ -53,7 +53,7 @@ impl<'a, I: FromStr> LineParser<'a, I> {
     }
 }
 
-impl<'a, I: FromStr> Iterator for LineParser<'a, I> {
+impl<I: FromStr> Iterator for LineParser<'_, I> {
     type Item = I;
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -61,6 +61,15 @@ impl<'a, I: FromStr> Iterator for LineParser<'a, I> {
     }
 }
 
+impl<'a, I: FromStr> From<LineIter<'a>> for LineParser<'a, I> {
+    fn from(iter: LineIter<'a>) -> Self {
+        Self {
+            iter,
+            _data: PhantomData,
+        }
+    }
+}
+
 /// Return two arguments in their natural PartialOrd order
 pub fn ordered<O: PartialOrd>(a: O, b: O) -> (O, O) {
     if a < b {