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+# Wrapping errors
+
+An alternative to boxing errors is to wrap them in your own error type.
+
+```rust,editable
+use std::error;
+use std::error::Error;
+use std::num::ParseIntError;
+use std::fmt;
+
+type Result<T> = std::result::Result<T, DoubleError>;
+
+#[derive(Debug)]
+enum DoubleError {
+    EmptyVec,
+    // We will defer to the parse error implementation for their error.
+    // Supplying extra info requires adding more data to the type.
+    Parse(ParseIntError),
+}
+
+impl fmt::Display for DoubleError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            DoubleError::EmptyVec =>
+                write!(f, "please use a vector with at least one element"),
+            // The wrapped error contains additional information and is available
+            // via the source() method.
+            DoubleError::Parse(..) =>
+                write!(f, "the provided string could not be parsed as int"),
+        }
+    }
+}
+
+impl error::Error for DoubleError {
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+        match *self {
+            DoubleError::EmptyVec => None,
+            // The cause is the underlying implementation error type. Is implicitly
+            // cast to the trait object `&error::Error`. This works because the
+            // underlying type already implements the `Error` trait.
+            DoubleError::Parse(ref e) => Some(e),
+        }
+    }
+}
+
+// Implement the conversion from `ParseIntError` to `DoubleError`.
+// This will be automatically called by `?` if a `ParseIntError`
+// needs to be converted into a `DoubleError`.
+impl From<ParseIntError> for DoubleError {
+    fn from(err: ParseIntError) -> DoubleError {
+        DoubleError::Parse(err)
+    }
+}
+
+fn double_first(vec: Vec<&str>) -> Result<i32> {
+    let first = vec.first().ok_or(DoubleError::EmptyVec)?;
+    // Here we implicitly use the `ParseIntError` implementation of `From` (which
+    // we defined above) in order to create a `DoubleError`.
+    let parsed = first.parse::<i32>()?;
+
+    Ok(2 * parsed)
+}
+
+fn print(result: Result<i32>) {
+    match result {
+        Ok(n)  => println!("The first doubled is {}", n),
+        Err(e) => {
+            println!("Error: {}", e);
+            if let Some(source) = e.source() {
+                println!("  Caused by: {}", source);
+            }
+        },
+    }
+}
+
+fn main() {
+    let numbers = vec!["42", "93", "18"];
+    let empty = vec![];
+    let strings = vec!["tofu", "93", "18"];
+
+    print(double_first(numbers));
+    print(double_first(empty));
+    print(double_first(strings));
+}
+```
+
+This adds a bit more boilerplate for handling errors and might not be needed in
+all applications. There are some libraries that can take care of the boilerplate
+for you.
+
+### See also:
+
+[`From::from`][from] and [`Enums`][enums]
+
+[from]: https://doc.rust-lang.org/std/convert/trait.From.html
+[enums]: ../../custom_types/enum.md