Why lifetimes exist in Rust - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a reference with a lifetime.

Rust

fn print_str<[1]>(s: &[1] str) { println!("{}", s); }

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

A'a

Bstatic

Cmut

Dref

Attempts:

3 left

💡 Hint

Common Mistakes

Using mut or ref instead of a lifetime parameter.

The 'a syntax declares a lifetime parameter for the reference &'a str.

2fill in blank

medium

Complete the function signature to specify that the returned reference has the same lifetime as the input.

Rust

fn first_char<[1]>(s: &[1] str) -> &[1] str { &s[0..1] }

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A'static

B'b

C'a

D'z

Attempts:

3 left

💡 Hint

Common Mistakes

Using different lifetime names for input and output.

The lifetime 'a is used to link the input and output lifetimes, ensuring the returned reference is valid as long as the input.

3fill in blank

hard

Fix the error by adding the correct lifetime annotation to the struct.

Rust

struct Holder<[1]> { value: &[1] str }

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A'a

B'static

C'b

D'z

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the lifetime parameter or using inconsistent names.

The struct needs a lifetime parameter 'a to specify how long the reference inside it is valid.

4fill in blank

hard

Fill both blanks to define a function that returns the longer of two string slices with correct lifetimes.

Rust

fn longer<'[1]>(x: &'[1] str, y: &'[1] str) -> &'[2] str { if x.len() > y.len() { x } else { y } }

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

Aa

Bb

Cc

Dd

Attempts:

3 left

💡 Hint

Common Mistakes

Using different lifetime names for inputs and output.

The lifetime 'a is used consistently to tie the input references and the output reference together.

5fill in blank

hard

Fill all three blanks to define a struct with two references having different lifetimes.

Rust

struct Pair<'[1], '[2]> { first: &'[1] str, second: &'[2] str }

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

Aa

Bb

Cc

Dd

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same lifetime for both references when different lifetimes are needed.

The struct uses two different lifetime parameters 'a and 'b for its two references.