Lifetime elision rules in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a function that returns a reference to the first element of a slice.

Rust

fn first_element(slice: &[i32]) -> &[1] {
    &slice[0]
}

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Abool

Bstr

Ci32

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different type than the slice element type.

Forgetting to use a reference in the return type.

The function returns a reference to an i32 because the slice contains i32 elements.

2fill in blank

medium

Complete the function signature to use lifetime elision correctly for a function returning the longer of two string slices.

Rust

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

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AString

Bstr

Cchar

Dusize

Attempts:

3 left

💡 Hint

Common Mistakes

Using String instead of str in the return type.

Omitting the lifetime parameter in the return type.

The function returns a string slice reference, so the return type is &'a str.

3fill in blank

hard

Fix the error in the function signature by adding the correct lifetime elision for a method returning a reference to self's name.

Rust

impl Person {
    fn name(&[1] self) -> &str {
        &self.name
    }
}

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A'_

B'a

C'static

D'self

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined lifetime parameters like 'a or 'self.

Using 'static which is too restrictive.

Using the anonymous lifetime '_ allows Rust to apply lifetime elision rules automatically for method receivers.

4fill in blank

hard

Fill both blanks to complete the function that returns a reference to the longer string slice using lifetime elision rules.

Rust

fn longest_with_announcement<'a, T>(x: &'a str, y: &'a str, ann: T) -> &'a [1] 
where
    T: std::fmt::Display,
{
    println!("Announcement: {}", ann);
    if x.len() [2] y.len() { x } else { y }
}

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Astr

B>

C<

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using String instead of str as return type.

Using '<' instead of '>' in the length comparison.

The return type is a string slice reference 'str', and the comparison uses '>' to check which string is longer.

5fill in blank

hard

Fill all three blanks to complete the struct and impl that uses lifetime elision rules for a reference field and a method returning that reference.

Rust

struct ImportantExcerpt<'a> {
    part: &[1] [2]
}

impl<'a> ImportantExcerpt<'a> {
    fn level(&[3] self) -> i32 {
        3
    }
}

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Astr

B'a

C'_

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using String instead of str for the field type.

Omitting the lifetime parameter for the reference field.

Using incorrect lifetime annotations for self.

The struct field is a reference to a string slice with lifetime 'a, and the method uses the anonymous lifetime '_' for self.