55 lines
1.6 KiB
Rust
55 lines
1.6 KiB
Rust
// box1.rs
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//
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// At compile time, Rust needs to know how much space a type takes up. This becomes problematic
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// for recursive types, where a value can have as part of itself another value of the same type.
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// To get around the issue, we can use a `Box` - a smart pointer used to store data on the heap,
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// which also allows us to wrap a recursive type.
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//
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// The recursive type we're implementing in this exercise is the `cons list` - a data structure
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// frequently found in functional programming languages. Each item in a cons list contains two
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// elements: the value of the current item and the next item. The last item is a value called `Nil`.
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//
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// Step 1: use a `Box` in the enum definition to make the code compile
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// Step 2: create both empty and non-empty cons lists by replacing `todo!()`
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//
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// Note: the tests should not be changed
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//
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// Execute `rustlings hint box1` or use the `hint` watch subcommand for a hint.
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#[derive(PartialEq, Debug)]
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pub enum List {
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Cons(i32, Box<List>),
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Nil,
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}
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fn main() {
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println!("This is an empty cons list: {:?}", create_empty_list());
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println!(
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"This is a non-empty cons list: {:?}",
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create_non_empty_list()
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);
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}
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pub fn create_empty_list() -> List {
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List::Nil
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}
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pub fn create_non_empty_list() -> List {
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List::Cons(1, Box::new(List::Cons(2, Box::new(List::Nil))))
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_create_empty_list() {
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assert_eq!(List::Nil, create_empty_list())
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}
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#[test]
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fn test_create_non_empty_list() {
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assert_ne!(create_empty_list(), create_non_empty_list())
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}
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}
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