rustLogic errorMedium

Unexpected empty output from a Rust function using.map()

Time: 0:00

BugFind the bug and fix the code

What it should do

Transform a vector of integers by doubling each element. Example: f([1, 2, 3]) -> [2, 4, 6]

What happens instead

The function returns an empty vector instead of the expected transformed vector.

fn transform_vector(vec: Vec<i32>) -> Vec<i32> {
  vec.iter().map(|x| x * 2);
  vec
}

fn main() {
  let vec = vec![1, 2, 3];
  let result = transform_vector(vec);
  println!("{:?}", result);
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

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rustLogic errorMedium

Unexpected empty output from a Rust function using.map()

Time: 0:00

BugFind the bug and fix the code

What it should do

Transform a vector of integers by doubling each element. Example: f([1, 2, 3]) -> [2, 4, 6]

What happens instead

The function returns an empty vector instead of the expected transformed vector.

fn transform_vector(vec: Vec<i32>) -> Vec<i32> {
  vec.iter().map(|x| x * 2);
  vec
}

fn main() {
  let vec = vec![1, 2, 3];
  let result = transform_vector(vec);
  println!("{:?}", result);
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

Unexpected empty output from a Rust function using.map()

What it should do

What happens instead

More logic errors to practise

Unexpected empty output from a Rust function using.map()

What it should do

What happens instead

More logic errors to practise