From 27b6165202b22ecfdee4b8a984e97b49f1225ea6 Mon Sep 17 00:00:00 2001
From: Andrew Walbran <qwandor@google.com>
Date: Mon, 16 Jan 2023 17:53:43 +0000
Subject: [PATCH] Implement Error.

---
 src/error-handling/converting-error-types.md | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/error-handling/converting-error-types.md b/src/error-handling/converting-error-types.md
index 2f5aaf10..debac80d 100644
--- a/src/error-handling/converting-error-types.md
+++ b/src/error-handling/converting-error-types.md
@@ -19,8 +19,10 @@ The `From::from` call here means we attempt to convert the error type to the
 type returned by the function:
 
 ```rust,editable
+use std::error::Error;
 use std::{fs, io};
 use std::io::Read;
+use std::fmt::{self, Display, Formatter};
 
 #[derive(Debug)]
 enum ReadUsernameError {
@@ -28,6 +30,17 @@ enum ReadUsernameError {
     EmptyUsername(String),
 }
 
+impl Error for ReadUsernameError {}
+
+impl Display for ReadUsernameError {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match self {
+            Self::IoError(e) => write!(f, "IO error: {}", e),
+            Self::EmptyUsername(filename) => write!(f, "Found no username in {}", filename),
+        }
+    }
+}
+
 impl From<io::Error> for ReadUsernameError {
     fn from(err: io::Error) -> ReadUsernameError {
         ReadUsernameError::IoError(err)