From 2e2f6b945dece8e6b3706f50722fa1774aa17944 Mon Sep 17 00:00:00 2001
From: Daniel Wagner-Hall <dawagner@gmail.com>
Date: Thu, 31 Oct 2024 13:45:28 +0000
Subject: [PATCH] Re-order actions you can take with a Result
It's generally better practice to handle or propagate errors, rather
than panicking in response to them. This edit moves panicking to be the
_last_ option introduced, rather than the first. It also adds caveats to
avoid doing so, and explicitly mentions propagating as something to
consider.
---
book/src/05_ticket_v2/07_unwrap.md | 33 ++++++++++++++++++++++--------
1 file changed, 24 insertions(+), 9 deletions(-)
diff --git a/book/src/05_ticket_v2/07_unwrap.md b/book/src/05_ticket_v2/07_unwrap.md
index ba67eedcdc..4088c1d864 100644
--- a/book/src/05_ticket_v2/07_unwrap.md
+++ b/book/src/05_ticket_v2/07_unwrap.md
@@ -21,16 +21,8 @@ let number = parse_int("42") + 2;
## You got a `Result`. Now what?
-When you call a function that returns a `Result`, you have two key options:
+When you call a function that returns a `Result`, you have three key options:
-- Panic if the operation failed.
- This is done using either the `unwrap` or `expect` methods.
- ```rust
- // Panics if `parse_int` returns an `Err`.
- let number = parse_int("42").unwrap();
- // `expect` lets you specify a custom panic message.
- let number = parse_int("42").expect("Failed to parse integer");
- ```
- Destructure the `Result` using a `match` expression to deal with the error case explicitly.
```rust
match parse_int("42") {
@@ -38,3 +30,26 @@ When you call a function that returns a `Result`, you have two key options:
Err(err) => eprintln!("Error: {}", err),
}
```
+- Propagate the error. If you're in a function which also returns a `Result`, you can use the `?` operator to early-return an error if it occurred:
+ ```rust
+ let number = parse_int("42")?;
+ println!("Parsed number: {}", number);
+ ```
+
+ The `?` operator works the same as manually destructuring the result and early returning:
+ ```rust
+ let number = match parse_int("42") {
+ Ok(number) => number,
+ Err(err) => return Err(err),
+ };
+ println!("Parsed number: {}", number);
+ ```
+- Panic if the operation failed.\
+ This is done using either the `unwrap` or `expect` methods.\
+ This this should generally only be done in your top-level `main` function - most functions should propagate errors rather than panic.
+ ```rust
+ // Panics if `parse_int` returns an `Err`.
+ let number = parse_int("42").unwrap();
+ // `expect` lets you specify a custom panic message.
+ let number = parse_int("42").expect("Failed to parse integer");
+ ```