Rust Function: Borrow String Slice, Get first character

Last update on December 21 2024 10:21:07 (UTC/GMT +8 hours)

Write a Rust function that borrows a string slice and returns its first character.

Sample Solution:

Rust Code:

// Define a function named 'get_first_char' that borrows a string slice and returns its first character
fn get_first_char(s: &str) -> Option<char> {
    s.chars().next() // Return an Option containing the first character of the string slice, or None if the string is empty
}

fn main() {
    let my_string = "Hello, world!"; // Define a string slice

    // Call the 'get_first_char' function and pass a reference to 'my_string' to borrow it
    match get_first_char(&my_string) {
        Some(first_char) => {
            println!("First character of the string: {}", first_char);
        }
        None => {
            println!("The string is empty.");
        }
    }

    // 'my_string' is still accessible here because we only borrowed it
    println!("Used 'my_string' after borrowing: {}", my_string);
}

Output:

First character of the string: H
Used 'my_string' after borrowing: Hello, world!

Explanation:

Here is a brief explanation of the above Rust code:

• fn get_first_char(s: &str) -> Option<char> { ... }: This is a function named get_first_char that borrows a string slice (&str) and returns an Option. The function returns 'Some' containing the first character of the string slice if it exists, or 'None' if the string is empty. The parameter 's' is of type '&str', indicating borrowing.
• Inside the function:
• We use the "chars()" method to obtain an iterator over the characters of the string slice.
• We use the "next()" method to retrieve the first character of the iterator, which returns an 'Option<char>'.
• In the main function,
• Define a string slice named 'my_string'.
• We then call the "get_first_char()" function and pass a reference to my_string (&my_string) to borrow it.
• We match on the result:
• If "Some", we print the value of the first character.
• If 'None', we print a message indicating that the string is empty.
• 'my_string' remains accessible after borrowing because we only borrowed it and didn't transfer ownership.

Rust Code Editor:

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