% Closures

There is a new edition of the book and this is an old link.

Anonymous functions you can save in a variable or pass as arguments to other functions.

# use std::thread;
# use std::time::Duration;

let expensive_closure = |num| {
    println!("calculating slowly...");
    thread::sleep(Duration::from_secs(2));
    num
};
# expensive_closure(5);

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Here are the relevant sections in the new and old books:

• in the current edition: Ch 13.01 — Closures
• In the first edition: Ch 3.23 — Closures