Rust errors: Difference between revisions
From wikinotes
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The <code>?</code> operator returns with the <code>Err</code> if it errored.<br> | The <code>?</code> operator returns with the <code>Err</code> if it errored.<br> | ||
You'll only need to provide the <code>Ok()</code> value. | You'll only need to provide the <code>Ok()</code> value.<br> | ||
(note you can also pass an Option and receive an Option in the same manner) | |||
<syntaxhighlight lang="rust"> | <syntaxhighlight lang="rust"> | ||
fn print_if_result_ok( | fn print_if_result_ok(i: isize) -> Result<String, MyError> { | ||
let result = is_one( | let result = is_one(i)? // return Err() if err | ||
println!("success value: {}", result); | println!("success value: {}", result); // unwraps result, and you know it is Ok() now | ||
Ok("success") | Ok("success") | ||
} | } | ||
</syntaxhighlight> | </syntaxhighlight> | ||
}} | }} | ||
</blockquote><!-- Result --> | </blockquote><!-- Result --> |
Revision as of 18:44, 8 February 2023
Rust has two primary methods of handling errors.
panic!()
halts/exits the programResult
types are for handle-able errors
panic
- intended for halting application, not control flow
- have backtraces
panic!("tried to X but couldn't Y") // convert panic to result // (not intended for native rust code) let result = panic::catch_unwind(|| { panic!("oh no!"); });
Result
The result type is an enum, whose options
Ok, Err
have been merged into the global scope throughprelude
.Given this Result producing code:
struct MyError { value: isize } fn is_one(i: isize) -> Result<String, MyError> { if i == 1 { Ok("success".to_string()) } else { Err(MyError{value: i}) } }
match
the various cases
let result = match is_one(2) { Ok(x) => format!("horay: {}", x), Err(_) => panic!("an error occurred") }; println!("{}", result);Panic if not successful
// panic if error, otherwise return value let result = is_one(2) .unwrap() // panic with message if error, otherwise return value let result = is_one(2) .expect("an error occurred!") // <-- panic messagePropagate the error if not successful
It's also fairly common that you want to delegate handling the error to the caller.
There is also syntactic sugar for this.The
?
operator returns with theErr
if it errored.
You'll only need to provide theOk()
value.
(note you can also pass an Option and receive an Option in the same manner)fn print_if_result_ok(i: isize) -> Result<String, MyError> { let result = is_one(i)? // return Err() if err println!("success value: {}", result); // unwraps result, and you know it is Ok() now Ok("success") }