Why does my variable not live long enough?

Question

I have a simple piece of code that is supposed to read a file into a vector by lines

use std::io::{self, Read};
use std::fs::File;

fn file_to_vec(filename: &str) -> Result<Vec<&str>, io::Error> {
    let mut file = try!(File::open(filename));
    let mut string = String::new();
    try!(file.read_to_string(&mut string));
    string.replace("\r", "");

    let data: Vec<&str> = string.split('\n').collect();

    Ok(data)
}

fn main() {}

I am getting the following error:

error[E0597]: `string` does not live long enough
  --> src/main.rs:10:27
   |
10 |     let data: Vec<&str> = string.split('\n').collect();
   |                           ^^^^^^ does not live long enough
...
13 | }
   | - borrowed value only lives until here
   |
note: borrowed value must be valid for the anonymous lifetime #1 defined on the function body at 4:1...
  --> src/main.rs:4:1
   |
4  | / fn file_to_vec(filename: &str) -> Result<Vec<&str>, io::Error> {
5  | |     let mut file = try!(File::open(filename));
6  | |     let mut string = String::new();
7  | |     try!(file.read_to_string(&mut string));
...  |
12 | |     Ok(data)
13 | | }
   | |_^

Why do I keep getting this error? How do I fix this? I imagine that it has something to do with the split method.

I could return the string and then split it into a Vec in the main function, but I really want to return a vector.

Answer 1

The problem is that string is created in your function and will be destroyed when the function returns. The vector you want to return contains slices of string, but those will not be valid outside of your function.

If you're not terribly worried about performance, you can return a Vec<String> from your function. You just have to return type to Result<Vec<String>, io::Error> and change the line

let data: Vec<&str> = string.split('\n').collect();

to

let data: Vec<String> = string.split('\n').map(String::from).collect();