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rustlings/exercises/19_smart_pointers/box1.rs

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// 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.
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//
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// The recursive type we're implementing in this exercise is the "cons list", a
// data structure frequently found in functional programming languages. Each
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// 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`.
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// TODO: Use a `Box` in the enum definition to make the code compile.
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#[derive(PartialEq, Debug)]
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enum List {
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Cons(i32, List),
Nil,
}
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// TODO: Create an empty cons list.
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fn create_empty_list() -> List {
todo!()
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}
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// TODO: Create a non-empty cons list.
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fn create_non_empty_list() -> List {
todo!()
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}
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fn main() {
println!("This is an empty cons list: {:?}", create_empty_list());
println!(
"This is a non-empty cons list: {:?}",
create_non_empty_list(),
);
}
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#[cfg(test)]
mod tests {
use super::*;
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#[test]
fn test_create_empty_list() {
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assert_eq!(create_empty_list(), List::Nil);
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}
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#[test]
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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}