Rust Programming: Shortcuts for Panic on Error: unwrap and expect

The Rust programming language provides two shortcut methods for handling errors: unwrap() and expect(). These methods are useful for cases where you are certain that the operation will succeed, and you want to avoid having to write a verbose match expression.

unwrap()

The unwrap() method returns the value inside the Ok variant of a Result enum, or panics with a default error message if the result is an Err.

Here is an example:

Rust

use std::fs::File;

fn main() {
    let greeting_file = File::open("hello.txt").unwrap();
}

If the hello.txt file does not exist, this code will panic with the following error message:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Os {
code: 2, kind: NotFound, message: "No such file or directory" }',
src/main.rs:4:49

expect()

The expect() method is similar to unwrap(), but it allows you to provide a custom error message if the operation fails.

Here is an example:

Rust

use std::fs::File;

fn main() {
    let greeting_file = File::open("hello.txt")
        .expect("hello.txt should be included in this project");
}

If the hello.txt file does not exist, this code will panic with the following error message:

thread 'main' panicked at 'hello.txt should be included in this project: Os {
code: 2, kind: NotFound, message: "No such file or directory" }',
src/main.rs:5:10

Which method to use?

In general, it is best to avoid using unwrap() and expect(), unless you are certain that the operation will succeed. If it is possible for the operation to fail, you should use a match expression to handle the error explicitly.

However, there are some cases where using unwrap() or expect() can be justified. For example, if you are reading a file from a predefined location, and you are certain that the file will always exist, then you can use unwrap() to avoid writing a verbose match expression.

Another case where using expect() can be justified is if you are debugging your code. If you are trying to figure out why a particular operation is failing, you can use expect() with a custom error message to get more information about the error.