Niche Optimization
#[derive(Debug)]
enum List<T> {
Cons(T, Box<List<T>>),
Nil,
}
fn main() {
let list: List<i32> = List::Cons(1, Box::new(List::Cons(2, Box::new(List::Nil))));
println!("{list:?}");
}
A Box
cannot be empty, so the pointer is always valid and non-null
. This allows the compiler to optimize the memory layout: