Rust Error: value of type `std::vec::Vec` cannot be built from `std::iter::Iterator`

I am new to rust and encountered the error

std::vec::Vec<i32> cannot be built from std::iter::Iterator<Item=&i32>

when trying to use a function get_even_numbers() to borrow v by passing it in by reference &v instead of by value v.

fn main() { let v: Vec<i32> = (0..10).collect(); let even: Vec<i32> = get_even_numbers(&v); println!("Even numbers: {:?}", even); } fn get_even_numbers(v: &Vec<i32>) -> Vec<i32> { v.iter().filter(|x| x % 2 == 0).collect() } 

Why does the above give an error, but passing it in by value does not, as shown below?

Additionally, I used .iter() inside the function when passing in by reference and .into_iter() when passing in by value, not sure if these are the correct functions to use.

fn main() { let v: Vec<i32> = (0..10).collect(); let even: Vec<i32> = get_even_numbers(v); println!("Even numbers: {:?}", even); } fn get_even_numbers(v: Vec<i32>) -> Vec<i32> { v.into_iter().filter(|x| x % 2 == 0).collect() } // Even numbers: [0, 2, 4, 6, 8] 

1 Answer

Use v.iter().filter(|x| x % 2 == 0).cloned().collect(). That will (trivially) clone each of the &i32 references into actual i32 values.