Generic functions in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a generic function that returns the input value.

Rust

fn identity<T>(value: T) -> T {
    return [1];
}

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

Areturn

BT

Cidentity

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the type name instead of the parameter.

Using the function name instead of the parameter.

The function returns the input parameter value directly.

2fill in blank

medium

Complete the code to call the generic function with an integer argument.

Rust

fn main() {
    let result = identity::<[1]>(5);
    println!("{}", result);
}

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

Ai32

Bf64

CString

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using a floating-point type like f64 for an integer argument.

Using a non-numeric type like String.

The generic type parameter is specified as i32 to match the integer argument 5.

3fill in blank

hard

Fix the error in the generic function declaration by completing the missing syntax.

Rust

fn [1]<T>(x: T) -> T {
    x
}

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

Aidentity

Bgeneric

Cprint

Dmain

Attempts:

3 left

💡 Hint

Common Mistakes

Using main which is reserved for the program entry point.

Using unrelated names like print.

The function name identity matches the intended generic function.

4fill in blank

hard

Fill both blanks to define a generic function that swaps two values and returns a tuple.

Rust

fn swap<T>(a: T, b: T) -> ([1], [2]) {
    (b, a)
}

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

AT

Bi32

Cf64

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using different types for the tuple elements.

Using concrete types like i32 or String.

The function returns a tuple of the same generic type T for both elements.

5fill in blank

hard

Fill all three blanks to complete a generic function that compares two values and returns the greater one.

Rust

fn max_value<T: PartialOrd>(a: T, b: T) -> [1] {
    if a [2] b {
        [3]
    } else {
        b
    }
}

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

AT

B>

Ca

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a boolean instead of a value.

Using the wrong comparison operator.

Returning the wrong variable.

The function returns a value of type T. It compares a and b using the > operator and returns a if it is greater.

Practice

1. What does the <T> mean in a Rust function definition like fn example<T>(value: T) {}?

easy

A. It makes the function generic, so it can accept any type.

B. It defines a new variable inside the function.

C. It restricts the function to only work with integers.

D. It marks the function as unsafe.

Solution

1. Step 1: Understand the syntax <T> in Rust

   The <T> after the function name declares a generic type parameter named T.

2. Step 2: Explain the effect of generic type parameter

   This allows the function to accept any type for value, making it flexible and reusable.

3. Final Answer:

   It makes the function generic, so it can accept any type. -> Option A

4. Quick Check:

   Generic type parameter = flexible function input [OK]

Hint: Look for <T> after function name for generics [OK]

Common Mistakes:

• Thinking <T> is a variable declaration
• Assuming it restricts to one type like integer
• Confusing it with unsafe code marker

2. Which of the following is the correct syntax to define a generic function named print_value that takes one argument of any type T?

easy

A. fn print_value(T value) {}

B. fn print_value<T>(value: T) {}

C. fn print_value(value: <T>) {}

D. fn print_value(value: T<>) {}

Solution

1. Step 1: Recall generic function syntax in Rust

   Generic functions use <T> after the function name to declare the generic type.

2. Step 2: Match the syntax with options

   fn print_value<T>(value: T) {} correctly places <T> after the function name and uses value: T as parameter type.

3. Final Answer:

   fn print_value<T>(value: T) {} -> Option B

4. Quick Check:

   Generic syntax = fn name<T>(param: T) [OK]

Hint: Generic type always goes after function name in angle brackets [OK]

Common Mistakes:

• Putting T inside parameter parentheses incorrectly
• Using angle brackets around parameter type
• Missing angle brackets after function name

3. What will be the output of this Rust code?

fn show_value<T: std::fmt::Display>(val: T) {
    println!("Value: {}", val);
}

fn main() {
    show_value(10);
    show_value("hello");
}

medium

A. Value: 10\nValue: hello

B. Value: 10\nValue: 10

C. Compilation error due to missing trait bound

D. Runtime error

Solution

1. Step 1: Understand the generic function with trait bound

   The function show_value requires T to implement Display so it can be printed.

2. Step 2: Check calls with integer and string

   Both 10 (integer) and "hello" (string) implement Display, so both calls print correctly.

3. Final Answer:

   Value: 10 Value: hello -> Option A

4. Quick Check:

   Trait bound allows printing = output shown [OK]

Hint: Check trait bounds to know if printing works [OK]

Common Mistakes:

• Assuming generic functions print without trait bounds
• Thinking string prints as number
• Expecting compilation error without trait bound

4. Identify the error in this generic function and how to fix it:

fn compare<T>(a: T, b: T) -> bool {
    a == b
}

medium

A. Function should return i32 instead of bool.

B. Function parameters should be references, not values.

C. Generic type T must be replaced with i32.

D. Missing trait bound T: PartialEq to use == operator.

Solution

1. Step 1: Understand use of == in generic function

   The == operator requires the type T to implement the PartialEq trait.

2. Step 2: Identify missing trait bound

   The function lacks T: PartialEq bound, so compiler will error when using ==.

3. Final Answer:

   Missing trait bound T: PartialEq to use == operator. -> Option D

4. Quick Check:

   Operator needs trait bound = add T: PartialEq [OK]

Hint: Add trait bounds when using operators on generics [OK]

Common Mistakes:

• Ignoring trait bounds for operators
• Changing return type unnecessarily
• Replacing generic with concrete type without reason

5. You want to write a generic function largest that returns the largest element from a slice of any type T. Which of these is the correct way to define it?

hard

A. fn largest<T>(list: &[T]) -> T { let mut largest = list[0]; for &item in list { if item > largest { largest = item; } } largest }

B. fn largest(list: &[i32]) -> i32 { let mut largest = list[0]; for &item in list { if item > largest { largest = item; } } largest }

C. fn largest<T: PartialOrd + Copy>(list: &[T]) -> T { let mut largest = *list[0]; for &item in list { if item > largest { largest = item; } } largest }

D. fn largest<T: PartialEq>(list: &[T]) -> T { list[0] }

Solution

1. Step 1: Identify required traits for comparison and copying

   To compare elements with >, T must implement PartialOrd. To copy elements, Copy trait is needed.

2. Step 2: Check function signature and body

   fn largest<T: PartialOrd + Copy>(list: &[T]) -> T { let mut largest = *list[0]; for &item in list { if item > largest { largest = item; } } largest } correctly adds T: PartialOrd + Copy and uses a loop to find the largest element.

3. Final Answer:

   fn largest<T: PartialOrd + Copy>(list: &[T]) -> T { ... } -> Option C

4. Quick Check:

   Traits PartialOrd + Copy needed for generic largest function [OK]

Hint: Add PartialOrd and Copy traits for generic comparisons [OK]

Common Mistakes:

• Omitting trait bounds causing compile errors
• Returning wrong type or missing copy trait
• Using concrete types instead of generics