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53 lines
1.4 KiB
Rust
53 lines
1.4 KiB
Rust
// At compile time, Rust needs to know how much space a type takes up. This
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// becomes problematic for recursive types, where a value can have as part of
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// itself another value of the same type. To get around the issue, we can use a
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// `Box` - a smart pointer used to store data on the heap, which also allows us
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// 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
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// 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
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// 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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#[derive(PartialEq, Debug)]
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enum List {
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Cons(i32, 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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fn create_empty_list() -> List {
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todo!()
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}
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fn create_non_empty_list() -> List {
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todo!()
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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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