Lifetimes in functions in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify a lifetime parameter for the function.

Rust

fn longest<'a>(x: &'a str, y: &str) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}

Drag options to blanks, or click blank then click option'

A'z

B'a

C'static

D'b

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to declare the lifetime parameter.

Using different lifetime names for input and output.

Using a lifetime on the parameter that is not linked to the output.

The lifetime parameter 'a is used to link the lifetime of the input x and the output reference.

2fill in blank

medium

Complete the code to declare the lifetime for both input parameters.

Rust

fn longest<'a>(x: &'a str, y: [1]) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}

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A&'a str

B&str

C&'static str

D&'b str

Attempts:

3 left

💡 Hint

Common Mistakes

Using &str without a lifetime.

Using a different lifetime like &'b str.

Using &'static str which is too restrictive.

Both input parameters must have the same lifetime 'a to ensure the output lifetime is valid.

3fill in blank

hard

Fix the error in the function signature by adding the correct lifetime to the return type.

Rust

fn first_word<'a>(s: &'a str) -> [1] {
    let bytes = s.as_bytes();
    for (i, &item) in bytes.iter().enumerate() {
        if item == b' ' {
            return &s[0..i];
        }
    }
    &s[..]
}

Drag options to blanks, or click blank then click option'

AString

B&str

C&'static str

D&'a str

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a reference without a lifetime.

Returning a String instead of a reference.

Using &'static str incorrectly.

The return type must have the same lifetime as the input reference to ensure safety.

4fill in blank

hard

Fill both blanks to correctly declare lifetimes for the function parameters and return type.

Rust

fn choose_first<'a, 'b>(x: &'a str, y: &'b str) -> [1] {
    x
}

fn choose_second<'a, 'b>(x: &'a str, y: &'b str) -> [2] {
    y
}

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A&'a str

B&'b str

C&str

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong lifetime for the return type.

Using &str without lifetime annotations.

Returning String instead of references.

The return type must match the lifetime of the reference returned from the function.

5fill in blank

hard

Fill all three blanks to correctly declare lifetimes and return a reference with the correct lifetime.

Rust

fn longest_with_announcement<'a>(x: &'a str, y: &'a str, ann: &str) -> [1] {
    println!("Announcement: {}", ann);
    if x.len() > y.len() {
        [2]
    } else {
        [3]
    }
}

Drag options to blanks, or click blank then click option'

A&'a str

B&'b str

Cx

Dy

Attempts:

3 left

💡 Hint

Common Mistakes

Not declaring lifetimes for the return type.

Returning values without matching lifetimes.

Using String instead of references.

The return type lifetime must match the lifetime of the returned reference. The function returns either x or y, so the lifetime must be declared accordingly.