New

A type without methods is a record, not an interface. We attach methods through impl blocks. The first one is a constructor.

1. 01
   Methods live in impl List { ... }. A function with no self is an associated function — call it as List::new(), the same way you'd call a static method.

   impl List {
       pub fn new() -> Self {
           List { head: Link::Empty }
       }
   }

2. 02
   Self (capital S) is shorthand for the type the impl block is on. Use it everywhere instead of repeating List; renaming the type later only touches the line pub struct List and not the constructor.

   let list = List::new();
   // list.head is Link::Empty