d10p2 trying question mark

day10/src/main.rs

@@ -1,3 +1,4 @@
+use std::num;
 use std::env;
 use std::process;
 use std::fs::File;
@@ -11,14 +12,16 @@ enum Inst{
 
 #[derive(Debug)]
 struct ParseError(String);
+impl From<num::ParseIntError> for ParseError {
+    fn from(e: num::ParseIntError) -> Self {
+        ParseError(e.to_string())
+    }
+}
 
 fn parse_line(line: String) -> Result<Inst, ParseError> {
     match &line[..4] {
         "noop" => Ok(Inst::Noop),
-        "addx" => match line[5..].parse::<i64>() {
-            Ok(operand) => Ok(Inst::AddX(operand)),
-            Err(e) => Err(ParseError(e.to_string())),
-        },
+        "addx" => Ok(Inst::AddX(line[5..].parse::<i64>()?)),
         _ => Err(ParseError(String::from("bad instruction"))),
     }
 }