Let’s decompose it one-by-one. Box Box<T> is a pointer to heap-allocated T. We use it here because trait objects can only exist behind pointers. Trait objects In Box<Fn() + Send + ‘static>, Fn() + Send + ‘static is a trait object type. In future, it will be written Box<dyn (Fn() + Send + ‘static)> to … Read more
It’s easiest to understand what non-lexical lifetimes are by understanding what lexical lifetimes are. In versions of Rust before non-lexical lifetimes are present, this code will fail: fn main() { let mut scores = vec![1, 2, 3]; let score = &scores[0]; scores.push(4); } The Rust compiler sees that scores is borrowed by the score variable, … Read more