Scoped Threads

Normal threads cannot borrow from their environment:

use std::thread;
fn main() {
    let s = String::from("Hello");
    thread::spawn(|| {
        println!("Length: {}", s.len());
    });
}

However, you can use a scoped thread for this:

use std::thread;
fn main() {
    let s = String::from("Hello");
    thread::scope(|scope| {
        scope.spawn(|| {
            println!("Length: {}", s.len());
        });
    });
}

• The reason for that is that when the thread::scope function completes, all the threads are guaranteed to be joined, so they can return borrowed data.
• Normal Rust borrowing rules apply: you can either borrow mutably by one thread, or immutably by any number of threads.