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Diffstat (limited to 'exercises/19_smart_pointers')
| -rw-r--r-- | exercises/19_smart_pointers/README.md | 12 | ||||
| -rw-r--r-- | exercises/19_smart_pointers/arc1.rs | 45 | ||||
| -rw-r--r-- | exercises/19_smart_pointers/box1.rs | 58 | ||||
| -rw-r--r-- | exercises/19_smart_pointers/cow1.rs | 78 | ||||
| -rw-r--r-- | exercises/19_smart_pointers/rc1.rs | 105 |
5 files changed, 298 insertions, 0 deletions
diff --git a/exercises/19_smart_pointers/README.md b/exercises/19_smart_pointers/README.md new file mode 100644 index 0000000..d56d2b6 --- /dev/null +++ b/exercises/19_smart_pointers/README.md @@ -0,0 +1,12 @@ +# Smart Pointers + +In Rust, smart pointers are variables that contain an address in memory and reference some other data, but they also have additional metadata and capabilities. +Smart pointers in Rust often own the data they point to, while references only borrow data. + +## Further Information + +- [Smart Pointers](https://doc.rust-lang.org/book/ch15-00-smart-pointers.html) +- [Using Box to Point to Data on the Heap](https://doc.rust-lang.org/book/ch15-01-box.html) +- [Rc\<T\>, the Reference Counted Smart Pointer](https://doc.rust-lang.org/book/ch15-04-rc.html) +- [Shared-State Concurrency](https://doc.rust-lang.org/book/ch16-03-shared-state.html) +- [Cow Documentation](https://doc.rust-lang.org/std/borrow/enum.Cow.html) diff --git a/exercises/19_smart_pointers/arc1.rs b/exercises/19_smart_pointers/arc1.rs new file mode 100644 index 0000000..3526ddc --- /dev/null +++ b/exercises/19_smart_pointers/arc1.rs @@ -0,0 +1,45 @@ +// arc1.rs +// +// In this exercise, we are given a Vec of u32 called "numbers" with values +// ranging from 0 to 99 -- [ 0, 1, 2, ..., 98, 99 ] We would like to use this +// set of numbers within 8 different threads simultaneously. Each thread is +// going to get the sum of every eighth value, with an offset. +// +// The first thread (offset 0), will sum 0, 8, 16, ... +// The second thread (offset 1), will sum 1, 9, 17, ... +// The third thread (offset 2), will sum 2, 10, 18, ... +// ... +// The eighth thread (offset 7), will sum 7, 15, 23, ... +// +// Because we are using threads, our values need to be thread-safe. Therefore, +// we are using Arc. We need to make a change in each of the two TODOs. +// +// Make this code compile by filling in a value for `shared_numbers` where the +// first TODO comment is, and create an initial binding for `child_numbers` +// where the second TODO comment is. Try not to create any copies of the +// `numbers` Vec! +// +// Execute `rustlings hint arc1` or use the `hint` watch subcommand for a hint. + +// I AM NOT DONE + +#![forbid(unused_imports)] // Do not change this, (or the next) line. +use std::sync::Arc; +use std::thread; + +fn main() { + let numbers: Vec<_> = (0..100u32).collect(); + let shared_numbers = // TODO + let mut joinhandles = Vec::new(); + + for offset in 0..8 { + let child_numbers = // TODO + joinhandles.push(thread::spawn(move || { + let sum: u32 = child_numbers.iter().filter(|&&n| n % 8 == offset).sum(); + println!("Sum of offset {} is {}", offset, sum); + })); + } + for handle in joinhandles.into_iter() { + handle.join().unwrap(); + } +} diff --git a/exercises/19_smart_pointers/box1.rs b/exercises/19_smart_pointers/box1.rs new file mode 100644 index 0000000..513e7da --- /dev/null +++ b/exercises/19_smart_pointers/box1.rs @@ -0,0 +1,58 @@ +// 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 by replacing `todo!()` +// +// Note: the tests should not be changed +// +// Execute `rustlings hint box1` or use the `hint` watch subcommand for a hint. + +// I AM NOT DONE + +#[derive(PartialEq, Debug)] +pub enum List { + Cons(i32, 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() + ); +} + +pub fn create_empty_list() -> List { + todo!() +} + +pub fn create_non_empty_list() -> List { + todo!() +} + +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn test_create_empty_list() { + assert_eq!(List::Nil, create_empty_list()) + } + + #[test] + fn test_create_non_empty_list() { + assert_ne!(create_empty_list(), create_non_empty_list()) + } +} diff --git a/exercises/19_smart_pointers/cow1.rs b/exercises/19_smart_pointers/cow1.rs new file mode 100644 index 0000000..fcd3e0b --- /dev/null +++ b/exercises/19_smart_pointers/cow1.rs @@ -0,0 +1,78 @@ +// cow1.rs +// +// This exercise explores the Cow, or Clone-On-Write type. Cow is a +// clone-on-write smart pointer. It can enclose and provide immutable access to +// borrowed data, and clone the data lazily when mutation or ownership is +// required. The type is designed to work with general borrowed data via the +// Borrow trait. +// +// This exercise is meant to show you what to expect when passing data to Cow. +// Fix the unit tests by checking for Cow::Owned(_) and Cow::Borrowed(_) at the +// TODO markers. +// +// Execute `rustlings hint cow1` or use the `hint` watch subcommand for a hint. + +// I AM NOT DONE + +use std::borrow::Cow; + +fn abs_all<'a, 'b>(input: &'a mut Cow<'b, [i32]>) -> &'a mut Cow<'b, [i32]> { + for i in 0..input.len() { + let v = input[i]; + if v < 0 { + // Clones into a vector if not already owned. + input.to_mut()[i] = -v; + } + } + input +} + +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn reference_mutation() -> Result<(), &'static str> { + // Clone occurs because `input` needs to be mutated. + let slice = [-1, 0, 1]; + let mut input = Cow::from(&slice[..]); + match abs_all(&mut input) { + Cow::Owned(_) => Ok(()), + _ => Err("Expected owned value"), + } + } + + #[test] + fn reference_no_mutation() -> Result<(), &'static str> { + // No clone occurs because `input` doesn't need to be mutated. + let slice = [0, 1, 2]; + let mut input = Cow::from(&slice[..]); + match abs_all(&mut input) { + // TODO + } + } + + #[test] + fn owned_no_mutation() -> Result<(), &'static str> { + // We can also pass `slice` without `&` so Cow owns it directly. In this + // case no mutation occurs and thus also no clone, but the result is + // still owned because it was never borrowed or mutated. + let slice = vec![0, 1, 2]; + let mut input = Cow::from(slice); + match abs_all(&mut input) { + // TODO + } + } + + #[test] + fn owned_mutation() -> Result<(), &'static str> { + // Of course this is also the case if a mutation does occur. In this + // case the call to `to_mut()` in the abs_all() function returns a + // reference to the same data as before. + let slice = vec![-1, 0, 1]; + let mut input = Cow::from(slice); + match abs_all(&mut input) { + // TODO + } + } +} diff --git a/exercises/19_smart_pointers/rc1.rs b/exercises/19_smart_pointers/rc1.rs new file mode 100644 index 0000000..1b90346 --- /dev/null +++ b/exercises/19_smart_pointers/rc1.rs @@ -0,0 +1,105 @@ +// rc1.rs +// +// In this exercise, we want to express the concept of multiple owners via the +// Rc<T> type. This is a model of our solar system - there is a Sun type and +// multiple Planets. The Planets take ownership of the sun, indicating that they +// revolve around the sun. +// +// Make this code compile by using the proper Rc primitives to express that the +// sun has multiple owners. +// +// Execute `rustlings hint rc1` or use the `hint` watch subcommand for a hint. + +// I AM NOT DONE + +use std::rc::Rc; + +#[derive(Debug)] +struct Sun {} + +#[derive(Debug)] +enum Planet { + Mercury(Rc<Sun>), + Venus(Rc<Sun>), + Earth(Rc<Sun>), + Mars(Rc<Sun>), + Jupiter(Rc<Sun>), + Saturn(Rc<Sun>), + Uranus(Rc<Sun>), + Neptune(Rc<Sun>), +} + +impl Planet { + fn details(&self) { + println!("Hi from {:?}!", self) + } +} + +#[test] +fn main() { + let sun = Rc::new(Sun {}); + println!("reference count = {}", Rc::strong_count(&sun)); // 1 reference + + let mercury = Planet::Mercury(Rc::clone(&sun)); + println!("reference count = {}", Rc::strong_count(&sun)); // 2 references + mercury.details(); + + let venus = Planet::Venus(Rc::clone(&sun)); + println!("reference count = {}", Rc::strong_count(&sun)); // 3 references + venus.details(); + + let earth = Planet::Earth(Rc::clone(&sun)); + println!("reference count = {}", Rc::strong_count(&sun)); // 4 references + earth.details(); + + let mars = Planet::Mars(Rc::clone(&sun)); + println!("reference count = {}", Rc::strong_count(&sun)); // 5 references + mars.details(); + + let jupiter = Planet::Jupiter(Rc::clone(&sun)); + println!("reference count = {}", Rc::strong_count(&sun)); // 6 references + jupiter.details(); + + // TODO + let saturn = Planet::Saturn(Rc::new(Sun {})); + println!("reference count = {}", Rc::strong_count(&sun)); // 7 references + saturn.details(); + + // TODO + let uranus = Planet::Uranus(Rc::new(Sun {})); + println!("reference count = {}", Rc::strong_count(&sun)); // 8 references + uranus.details(); + + // TODO + let neptune = Planet::Neptune(Rc::new(Sun {})); + println!("reference count = {}", Rc::strong_count(&sun)); // 9 references + neptune.details(); + + assert_eq!(Rc::strong_count(&sun), 9); + + drop(neptune); + println!("reference count = {}", Rc::strong_count(&sun)); // 8 references + + drop(uranus); + println!("reference count = {}", Rc::strong_count(&sun)); // 7 references + + drop(saturn); + println!("reference count = {}", Rc::strong_count(&sun)); // 6 references + + drop(jupiter); + println!("reference count = {}", Rc::strong_count(&sun)); // 5 references + + drop(mars); + println!("reference count = {}", Rc::strong_count(&sun)); // 4 references + + // TODO + println!("reference count = {}", Rc::strong_count(&sun)); // 3 references + + // TODO + println!("reference count = {}", Rc::strong_count(&sun)); // 2 references + + // TODO + println!("reference count = {}", Rc::strong_count(&sun)); // 1 reference + + assert_eq!(Rc::strong_count(&sun), 1); +} |