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78 lines
2.3 KiB
Rust
78 lines
2.3 KiB
Rust
// ./src/custom_types/enum/testcase_linked_list.md
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use crate::List::*;
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enum List {
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// Cons: Tuple struct that wraps an element and a pointer to the next node
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Cons(u32, Box<List>),
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// Nil: A node that signifies the end of the linked list
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Nil,
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}
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// Methods can be attached to an enum
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impl List {
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// Create an empty list
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fn new() -> List {
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// `Nil` has type `List`
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Nil
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}
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// Consume a list, and return the same list with a new element at its front
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fn prepend(self, elem: u32) -> List {
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// `Cons` also has type List
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Cons(elem, Box::new(self))
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}
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// Return the length of the list
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fn len(&self) -> u32 {
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// `self` has to be matched, because the behavior of this method
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// depends on the variant of `self`
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// `self` has type `&List`, and `*self` has type `List`, matching on a
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// concrete type `T` is preferred over a match on a reference `&T`
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// after Rust 2018 you can use self here and tail (with no ref) below as well,
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// rust will infer &s and ref tail.
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// See https://doc.rust-lang.org/edition-guide/rust-2018/ownership-and-lifetimes/default-match-bindings.html
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match *self {
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// Can't take ownership of the tail, because `self` is borrowed;
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// instead take a reference to the tail
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Cons(_, ref tail) => 1 + tail.len(),
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// Base Case: An empty list has zero length
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Nil => 0
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}
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}
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// Return representation of the list as a (heap allocated) string
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fn stringify(&self) -> String {
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match *self {
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Cons(head, ref tail) => {
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// `format!` is similar to `print!`, but returns a heap
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// allocated string instead of printing to the console
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format!("{}, {}", head, tail.stringify())
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},
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Nil => {
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format!("Nil")
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},
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}
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}
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}
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fn part0() {
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// Create an empty linked list
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let mut list = List::new();
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// Prepend some elements
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list = list.prepend(1);
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list = list.prepend(2);
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list = list.prepend(3);
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// Show the final state of the list
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println!("linked list has length: {}", list.len());
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println!("{}", list.stringify());
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}
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pub fn main() {
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part0();
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}
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