From 7479a4737bdcac347322ad0883ca528c8675e720 Mon Sep 17 00:00:00 2001 From: AlexandruGG Date: Tue, 26 May 2020 21:46:24 +0100 Subject: [PATCH] feat: Add box1.rs exercise --- exercises/standard_library_types/README.md | 2 ++ exercises/standard_library_types/box1.rs | 35 ++++++++++++++++++++++ info.toml | 18 +++++++++++ 3 files changed, 55 insertions(+) create mode 100644 exercises/standard_library_types/box1.rs diff --git a/exercises/standard_library_types/README.md b/exercises/standard_library_types/README.md index d138d87..36b30c1 100644 --- a/exercises/standard_library_types/README.md +++ b/exercises/standard_library_types/README.md @@ -1,3 +1,5 @@ +For the Box exercise check out the chapter [Using Box to Point to Data on the Heap](https://doc.rust-lang.org/book/ch15-01-box.html). + For the Arc exercise check out the chapter [Shared-State Concurrency](https://doc.rust-lang.org/book/ch16-03-shared-state.html) of the Rust Book. For the Iterator exercise check out the chapters [Iterator](https://doc.rust-lang.org/book/ch13-02-iterators.html) of the Rust Book and the [Iterator documentation](https://doc.rust-lang.org/stable/std/iter/). diff --git a/exercises/standard_library_types/box1.rs b/exercises/standard_library_types/box1.rs new file mode 100644 index 0000000..11156ea --- /dev/null +++ b/exercises/standard_library_types/box1.rs @@ -0,0 +1,35 @@ +// 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); +} diff --git a/info.toml b/info.toml index e2aa82a..dcd93bf 100644 --- a/info.toml +++ b/info.toml @@ -614,6 +614,24 @@ hint = """ # STANDARD LIBRARY TYPES +[[exercises]] +name = "box1" +path = "exercises/standard_library_types/box1.rs" +mode = "compile" +hint = """ +Step 1 +The compiler's message should help: since we cannot store the value of the actual type +when working with recursive types, we need to store a reference (pointer) to its value. +We should therefore place our `List` inside a `Box`. More details in the book here: +https://doc.rust-lang.org/book/ch15-01-box.html#enabling-recursive-types-with-boxes + +Step 2 +Creating an empty list should be fairly straightforward (hint: peek at the assertions). +For a non-empty list keep in mind that wee want to use our Cons "list builder". +Although the current list is one of integers (i32), feel free to change the definition +and try other types! +""" + [[exercises]] name = "arc1" path = "exercises/standard_library_types/arc1.rs"