Split out example to separate page. (#319)

The example is quite long and so the page didn't easily fit on the
same screen as the explanation

src/SUMMARY.md

@@ -153,6 +153,7 @@
   - [Structured Error Handling](error-handling/result.md)
   - [Propagating Errors with ?](error-handling/try-operator.md)
     - [Converting Error Types](error-handling/converting-error-types.md)
+      - [Example](error-handling/converting-error-types-example.md)
     - [Deriving Error Enums](error-handling/deriving-error-enums.md)
     - [Dynamic Error Types](error-handling/dynamic-errors.md)
     - [Adding Context to Errors](error-handling/error-contexts.md)

src/error-handling/converting-error-types-example.md

@@ -0,0 +1,60 @@
+# Converting Error Types
+
+```rust,editable
+use std::error::Error;
+use std::fmt::{self, Display, Formatter};
+use std::fs::{self, File};
+use std::io::{self, Read};
+
+#[derive(Debug)]
+enum ReadUsernameError {
+    IoError(io::Error),
+    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)
+    }
+}
+
+fn read_username(path: &str) -> Result<String, ReadUsernameError> {
+    let mut username = String::with_capacity(100);
+    File::open(path)?.read_to_string(&mut username)?;
+    if username.is_empty() {
+        return Err(ReadUsernameError::EmptyUsername(String::from(path)));
+    }
+    Ok(username)
+}
+
+fn main() {
+    //fs::write("config.dat", "").unwrap();
+    let username = read_username("config.dat");
+    println!("username or error: {username:?}");
+}
+```
+
+<details>
+
+Key points:
+
+* The `username` variable can be either `Ok(string)` or `Err(error)`.
+* Use the `fs::write` call to test out the different scenarios: no file, empty file, file with username.
+
+It is good practice for all error types to implement `std::error::Error`, which requires `Debug` and
+`Display`. It's generally helpful for them to implement `Clone` and `Eq` too where possible, to make
+life easier for tests and consumers of your library. In this case we can't easily do so, because
+`io::Error` doesn't implement them.
+
+</details>

src/error-handling/converting-error-types.md

@@ -17,62 +17,3 @@ match expression {
 
 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 {
-    IoError(io::Error),
-    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)
-    }
-}
-
-fn read_username(path: &str) -> Result<String, ReadUsernameError> {
-    let mut username = String::with_capacity(100);
-    fs::File::open(path)?.read_to_string(&mut username)?;
-    if username.is_empty() {
-        return Err(ReadUsernameError::EmptyUsername(String::from(path)));
-    }
-    Ok(username)
-}
-
-fn main() {
-    //fs::write("config.dat", "").unwrap();
-    let username = read_username("config.dat");
-    println!("username or error: {username:?}");
-}
-```
-
-<details>
-
-Key points:
-
-* The `username` variable can be either `Ok(string)` or `Err(error)`.
-* Use the `fs::write` call to test out the different scenarios: no file, empty file, file with username.
-
-It is good practice for all error types to implement `std::error::Error`, which requires `Debug` and
-`Display`. It's generally helpful for them to implement `Clone` and `Eq` too where possible, to make
-life easier for tests and consumers of your library. In this case we can't easily do so, because
-`io::Error` doesn't implement them.
-
-</details>