Extend lifetime of a variable for thread

Question

I am reading a string from a file, splitting it by lines into a vector and then I want to do something with the extracted lines in separate threads. Like this:

Answer 1

The problem, fundamentally, is that line is a borrowed slice into s. There's really nothing you can do here, since there's no way to guarantee that each line will not outlive s itself.

Also, just to be clear: there is absolutely no way in Rust to "extend the lifetime of a variable". It simply cannot be done.

The simplest way around this is to go from line being borrowed to owned. Like so:

use std::thread;
fn main() {
    let mut s: String = "One\nTwo\nThree\n".into();
    let k : Vec<String> = s.split("\n").map(|s| s.into()).collect();
    for line in k {
        thread::spawn(move || {
            println!("nL: {:?}", line);
        });
    }
}

The .map(|s| s.into()) converts from &str to String. Since a String owns its contents, it can be safely moved into each thread's closure, and will live independently of the thread that created it.

Note: you could do this in nightly Rust using the new scoped thread API, but that is still unstable.