A common use for enums is to create a linked-list:
>use crate::List::*;
>enum List {
>// Cons: Tuple struct that wraps an element and a pointer to the next node
>Cons(u32, Box),
>// Nil: A node that signifies the end of the linked list
>Nil,
>}
>// Methods can be attached to an enum
>impl List {
>// Create an empty list
>fn new() -> List {
>// `Nil` has type `List`
>Nil
>}
>// Consume a list, and return the same list with a new element at its front
>fn prepend(self, elem: u32) -> List {
>// `Cons` also has type List
>Cons(elem, Box::new(self))
>}
>// Return the length of the list
>fn len(&self) -> u32 {
>// `self` has to be matched, because the behavior of this method
>// depends on the variant of `self`
>// `self` has type `&List`, and `*self` has type `List`, matching on a
>// concrete type `T` is preferred over a match on a reference `&T`
>match *self {
>// Can't take ownership of the tail, because `self` is borrowed;
>// instead take a reference to the tail
>Cons(_, ref tail) => 1 + tail.len(),
>// Base Case: An empty list has zero length
>Nil => 0
>}
>}
>// Return representation of the list as a (heap allocated) string
>fn stringify(&self) -> String {
>match *self {
>Cons(head, ref tail) => {
>// `format!` is similar to `print!`, but returns a heap
>// allocated string instead of printing to the console
>format!("{}, {}", head, tail.stringify())
>},
>Nil => {
>format!("Nil")
>},
>}
>}
>}
>fn main() {
>// Create an empty linked list
>let mut list = List::new();
>// Prepend some elements
>list = list.prepend(1);
>list = list.prepend(2);
>list = list.prepend(3);
>// Show the final state of the list
>println!("linked list has length: {}", list.len());
>println!("{}", list.stringify());
>}
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