How to extract elements of a vector of strings in Rust?

Question

Let's say I have the following code:

fn extract() -> Vec<String> {
    let data = vec!["aaa".to_string(), "bbb".to_string(), "ccc".to_string()];
    vec![data[0], data[2]]
}

In practice, I read data from a file.

Obviously, this doesn't compile because I'm pulling strings out of the vector data, leaving the vector in an undefined state. But, conceptually, it should work, because I'm not using data afterwards anyway.

I can use mem::replace, but this seems crazy:

fn extract() -> Vec<String> {
    let mut data = vec!["aaa".to_string(), "bbb".to_string(), "ccc".to_string()];
    let a = mem::replace(&mut data[0], "".to_string());
    let c = mem::replace(&mut data[2], "".to_string());
    vec![a, c]
}

How do I go about extracting specific elements from the vector without having to clone the strings?

Answer 1

Vec has special methods for that. swap_remove, remove (warning, linear complexity), drain. For example,

fn extract() -> Vec<String> {
    let mut data = vec!["aaa".to_string(), "bbb".to_string(), "ccc".to_string()];
    // order does matter
    vec![data.swap_remove(2), data.swap_remove(0)]
}