Trait objects overview in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a trait object reference.

Rust

fn print_value(value: &[1]) {
    println!("Value printed");
}

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Adyn Display

BDisplay

C&Display

Ddyn Trait

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the 'dyn' keyword before the trait name.

Using the trait name without a reference.

Trait objects in Rust are declared using the 'dyn' keyword followed by the trait name, like 'dyn Display'.

2fill in blank

medium

Complete the code to create a boxed trait object.

Rust

let boxed: Box<[1]> = Box::new(5);

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ADisplay

Bdyn Debug

Cdyn Display

DDebug

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the 'dyn' keyword inside the Box.

Using the trait name without 'dyn' in Box.

Boxed trait objects use 'Box' syntax to store values on the heap with dynamic dispatch.

3fill in blank

hard

Fix the error in the function signature to accept any trait object implementing Debug.

Rust

fn debug_print(value: &[1]) {
    println!("{:?}", value);
}

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ADebug

B&Debug

Cdyn Display

Ddyn Debug

Attempts:

3 left

💡 Hint

Common Mistakes

Using the trait name without 'dyn'.

Using a reference to the trait without 'dyn'.

Trait objects must be referenced with 'dyn' keyword, so '&dyn Debug' is the correct type for dynamic dispatch.

4fill in blank

hard

Fill both blanks to create a vector of boxed trait objects implementing Display.

Rust

let mut vec: Vec<Box<[1]>> = Vec::new();
vec.push(Box::new("hello"));
vec.push(Box::new(123));
for item in vec.iter() {
    println!("{}", item.[2]());
}

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Adyn Display

Bdyn Debug

Cto_string

Dto_owned

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong trait in the vector type.

Calling a method that does not exist on the trait object.

The vector holds boxed 'dyn Display' trait objects, and calling 'to_string()' converts them to strings for printing.

5fill in blank

hard

Fill all three blanks to define a function returning a boxed trait object implementing Debug.

Rust

fn make_debug() -> Box<[1]> {
    let value = 42;
    Box::new(value) as Box<[2]>
}

fn main() {
    let debug_obj: Box<[3]> = make_debug();
    println!("{:?}", debug_obj);
}

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

Adyn Debug

Bdyn Display

Ddyn Any

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing different trait objects in return type and variable.

Omitting 'dyn' keyword in trait object types.

The function returns a boxed 'dyn Debug' trait object, so all blanks must be 'dyn Debug' to match the type.