mirror of
https://github.com/notohh/rustlings.git
synced 2024-11-22 05:52:23 -05:00
47 lines
1.3 KiB
Rust
47 lines
1.3 KiB
Rust
// At compile time, Rust needs to know how much space a type takes up. This
|
|
// becomes problematic for recursive types, where a value can have as part of
|
|
// itself another value of the same type. To get around the issue, we can use a
|
|
// `Box` - a smart pointer used to store data on the heap, which also allows us
|
|
// to wrap a recursive type.
|
|
//
|
|
// The recursive type we're implementing in this exercise is the "cons list", a
|
|
// data structure frequently found in functional programming languages. Each
|
|
// item in a cons list contains two elements: The value of the current item and
|
|
// the next item. The last item is a value called `Nil`.
|
|
|
|
#[derive(PartialEq, Debug)]
|
|
enum List {
|
|
Cons(i32, Box<List>),
|
|
Nil,
|
|
}
|
|
|
|
fn create_empty_list() -> List {
|
|
List::Nil
|
|
}
|
|
|
|
fn create_non_empty_list() -> List {
|
|
List::Cons(42, Box::new(List::Nil))
|
|
}
|
|
|
|
fn main() {
|
|
println!("This is an empty cons list: {:?}", create_empty_list());
|
|
println!(
|
|
"This is a non-empty cons list: {:?}",
|
|
create_non_empty_list(),
|
|
);
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use super::*;
|
|
|
|
#[test]
|
|
fn test_create_empty_list() {
|
|
assert_eq!(create_empty_list(), List::Nil);
|
|
}
|
|
|
|
#[test]
|
|
fn test_create_non_empty_list() {
|
|
assert_ne!(create_empty_list(), create_non_empty_list());
|
|
}
|
|
}
|