Rust Function: Borrow Vector, Get first element

Last update on December 21 2024 10:18:43 (UTC/GMT +8 hours)

Write a Rust function that borrows a vector and returns the first element.

Sample Solution:

Rust Code:

// Define a function named 'get_first_element' that borrows a vector and returns the first element
fn get_first_element(v: &[i32]) -> Option<&i32> {
    v.first() // Return an Option containing a reference to the first element of the vector, or None if the vector is empty
}

fn main() {
    let my_vector = vec![1, 2, 3, 4, 5]; // Define a vector

    // Call the 'get_first_element' function and pass a reference to 'my_vector' to borrow it
    match get_first_element(&my_vector) {
        Some(first_element) => {
            println!("First element of the vector: {}", first_element);
        }
        None => {
            println!("The vector is empty.");
        }
    }

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

Output:

First element of the vector: 1
Used 'my_vector' after borrowing: [1, 2, 3, 4, 5]

Explanation:

Here is a brief explanation of the above Rust code:

• fn get_first_element(v: &[i32]) -> Option<&i32> { ... }: This is a function named get_first_element that borrows a slice of a vector (&[i32]) and returns an Option<&i32>. The function returns 'Some' containing a reference to the first element of the vector if it exists, or 'None' if the vector is empty. The parameter 'v' is of type &[i32], indicating borrowing.
• Inside the function:
• We use the "first()" method to get an 'Option' containing a reference to the first element of the vector, or 'None' if the vector is empty.
• In the main function,
• We define a vector named 'my_vector'.
• We then call the "get_first_element()" function and pass a reference to 'my_vector' (&my_vector) to borrow it.
• We match on the result:
• If 'Some', we print the value of the first element.
• If 'None', we print a message indicating that the vector is empty.
• 'my_vector' remains accessible after borrowing because we only borrowed it and didn't transfer ownership.

Rust Code Editor:

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