Rust – Using Option enum for Error Handling

In Rust, while coding the focus is mainly on performance, safety, and concurrency. It specifically uses enums like Option<T> and Result<T> for handling errors. Option type in Rust generally denotes option values that have two attributes: Some and None. The option type creates an i32 box for using inner values.

Options <T> uses pattern matches for querying whether the value is present or not and in case there aren’t any, it references a nullable (None). Whenever there is a pattern match, the rust compiler assigns the box a value, and if there aren’t any then the box is empty.

Example 1:

Rust

#![allow(unused)]
fn main() {
let matching_digit = Some(100);
fn processing_digit(i: i32) {
println!("Inside Processing digit function!");
}
fn processing_other_digit(i: i32) {
println!("Inside Processing Other digit function!");

}
let msg = match matching_digit {
    Some(x) if x < 20 => processing_digit(x),
    Some(x)  => processing_digit(x),
    None => panic!(),
};
}

Output:

Explanation:

In this example, we have used a variable named matching_digit that holds a value passed by the Some() function. The function processing digit as well the function other_processing digit both accept 32-bit integers. Now, we pass a value of 100 and assign a condition to one of the Some parameters that if the value is less than 20 it will match and the processing_digit function would be called and if nothing is passed Rust will use None which would panic.

Example 2:

Rust

fn find(search: &str, variable: char) -> Option<usize> {search.find(variable) }
fn main() {
    let var_name = "GeeksforGeeks";
    match find(var_name, 'G') {
        None => println!("Letter not found"),
        Some(_i) => println!("Letter found"),
    }
}

Output:

Explanation:

In this example, we are finding the letter ‘G’ initially and we are checking using Some() whether the value is present or not. If it is present then var_name matches with the find function and we print Letter found in the output. 

Similarly, for another example, if we search for the letter ‘Z’ we won’t find it.

Example 3:

Rust

fn find(search: &str, variable: char) -> Option<usize> { search.find(variable) }
fn main() {
    let var_name = "GeeksforGeeks";
    match find(var_name, 'Z') {
        None => println!("Letter not found"),
        Some(_i) => println!("Letter found"),
    }
}

Output: