Variable lifetime basics in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable with a lifetime annotation.

Rust

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

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

A'z

B'static

C'b

D'a

Attempts:

3 left

💡 Hint

Common Mistakes

Using a lifetime that is not declared in the function signature.

Forgetting to add the lifetime annotation to the reference.

The lifetime parameter 'a is declared and used to annotate the reference s, ensuring it lives at least as long as 'a.

2fill in blank

medium

Complete the code to return a reference with the correct lifetime.

Rust

fn first_word<'a>(s: &'a str) -> &'a [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'

Achar

Bstr

Cusize

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a String instead of a string slice.

Omitting the lifetime annotation in the return type.

The function returns a string slice (&str) with the same lifetime 'a as the input reference.

3fill in blank

hard

Fix the error in the function signature by adding the correct lifetime annotation.

Rust

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

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

A'a

B'b

C'static

D'z

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the lifetime annotation in the return type.

Using different lifetimes for inputs and output.

The function returns a reference that must have a lifetime parameter 'a to relate the input lifetimes to the output.

4fill in blank

hard

Fill both blanks to define a struct with a lifetime and a reference field.

Rust

struct ImportantExcerpt[1] {
    part: &[2] str,
}

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A<'a>

B'static

C'a

D<'static>

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'static lifetime incorrectly.

Forgetting to declare the lifetime parameter on the struct.

The struct uses a lifetime parameter 'a declared as <'a> and the field part is a reference with lifetime 'a.

5fill in blank

hard

Fill all three blanks to implement a method that returns the part field with the correct lifetime.

Rust

impl[1] ImportantExcerpt[2] {
    fn level(&self) -> &[3] str {
        self.part
    }
}

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

A<'a>

B'a

D<'static>

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting lifetime parameters in impl or method.

Using inconsistent lifetimes between struct and method.

The impl block and struct use the lifetime parameter <'a>, and the method returns a reference with lifetime 'a.