36 lines
1.3 KiB
Rust
36 lines
1.3 KiB
Rust
|
// box1.rs
|
||
|
|
//
|
||
|
|
// 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`.
|
||
|
|
//
|
||
|
|
// Step 1: use a `Box` in the enum definition to make the code compile
|
||
|
|
// Step 2: create both empty and non-empty cons lists of by replacing `unimplemented!()`
|
||
|
|
//
|
||
|
|
// Execute `rustlings hint box1` for hints :)
|
||
|
|
|
||
|
|
// I AM NOT DONE
|
||
|
|
|
||
|
|
#[derive(PartialEq, Debug)]
|
||
|
|
enum List {
|
||
|
|
Cons(i32, List),
|
||
|
|
Nil,
|
||
|
|
}
|
||
|
|
|
||
|
|
fn main() {
|
||
|
|
let empty_list = unimplemented!();
|
||
|
|
println!("This is an empty cons list: {:?}", empty_list);
|
||
|
|
|
||
|
|
let non_empty_list = unimplemented!();
|
||
|
|
println!("This is a non-empty cons list: {:?}", non_empty_list);
|
||
|
|
|
||
|
|
// Do not change these
|
||
|
|
assert_eq!(List::Nil, empty_list);
|
||
|
|
assert_ne!(empty_list, non_empty_list);
|
||
|
|
}
|