What is Send and Sync

Send and Sync are marker traits in Rust that determine if a type can be safely transferred between threads or shared across threads. Send means a type can be moved to another thread, while Sync means a reference to the type can be safely shared between threads. Most standard types implement these automatically, but you must explicitly implement them for custom types used in concurrency.

use std::thread;

fn main() {
    let data = String::from("hello");
    thread::spawn(move || {
        println!("{}", data);
    }).join().unwrap();
}

Send and Sync are safety checks that tell the Rust compiler if your data is safe to use with multiple threads. Think of Send as a permission slip to move an item to a different room, and Sync as a rule allowing multiple people to look at the same item at once without breaking it. You use these concepts whenever you write code that runs tasks simultaneously to prevent crashes or data corruption.