Search if an Item Exists Inside a Collection in Rust

The Problem

In Python, you can use the in keyword to check if a value is present in a sequence (list, range, string, etc):

# a list of car makers
carmakers = ["Toyota", "Mercedes Benz", "BMW", "Honda"]

# check if BYD in list or not
if "BYD" in carmakers:
    print("BYD is in car makers")

How can we do it in Rust?

The Solution

We can do the same in Rust by using the if let statement to allows matching on various options on a variable.

For the example, let’s write a function in Rust to count the number of vowels (a, i, u, e, o) in a given word or sentence, regardless of case (i.e. A is the same with a):

pub fn count_vowels(strinput: String) -> i32 {
    let mut num_vowels: i32 = 0;
    for char in strinput.to_ascii_lowercase().chars() {
        if let 'a' | 'i' | 'u' | 'e' | 'o' = char {
            num_vowels += 1;
        }
    }
    num_vowels
}

The Tests

Now, let’s define our unit test:

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_count_vowels_in_a_sentence() {
        let sentence = String::from("Who are you?");
        let expected = 5;
        let result = count_vowels(sentence);
        assert_eq!(result, expected);
    }

    #[test]
    fn test_count_vowels_in_a_word() {
        let word = String::from("ASDsdaf!@3%sdsga#5shdsauyetow");
        let expected = 7;
        let result = count_vowels(word);
        assert_eq!(result, expected);
    }
}

Unit test result:

$ cargo test -q

running 2 tests
..
test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s


running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

You can check out the full code in this GitHub repo for more info.