Main exercises
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@ -4,7 +4,7 @@
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// This exercise uses some concepts that we won't get to until later in the course, like `Box` and the
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// `From` trait. It's not important to understand them in detail right now, but you can read ahead if you like.
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// For now, think of the `Box<dyn ...>` type as an "I want anything that does ???" type, which, given
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// For now, think of the `Box<dyn ???>` type as an "I want anything that does ???" type, which, given
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// Rust's usual standards for runtime safety, should strike you as somewhat lenient!
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// In short, this particular use case for boxes is for when you want to own a value and you care only that it is a
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@ -10,7 +10,7 @@
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// I AM NOT DONE
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fn main () {
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fn main() {
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let my_fav_fruits = vec!["banana", "custard apple", "avocado", "peach", "raspberry"];
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let mut my_iterable_fav_fruits = ???; // TODO: Step 1
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@ -3,6 +3,7 @@
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// I AM NOT DONE
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#[rustfmt::skip]
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macro_rules! my_macro {
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() => {
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println!("Check out my macro!");
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@ -32,7 +32,7 @@ fn main() {
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for offset in 0..8 {
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let child_numbers = // TODO
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joinhandles.push(thread::spawn(move || {
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let sum: u32 = child_numbers.iter().filter(|n| *n % 8 == offset).sum();
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let sum: u32 = child_numbers.iter().filter(|&&n| n % 8 == offset).sum();
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println!("Sum of offset {} is {}", offset, sum);
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}));
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}
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@ -4,6 +4,9 @@
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// Cow is a clone-on-write smart pointer.
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// It can enclose and provide immutable access to borrowed data, and clone the data lazily when mutation or ownership is required.
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// The type is designed to work with general borrowed data via the Borrow trait.
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//
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// This exercise is meant to show you what to expect when passing data to Cow.
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// Fix the unit tests by checking for Cow::Owned(_) and Cow::Borrowed(_) at the TODO markers.
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// I AM NOT DONE
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@ -20,29 +23,52 @@ fn abs_all<'a, 'b>(input: &'a mut Cow<'b, [i32]>) -> &'a mut Cow<'b, [i32]> {
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input
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}
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fn main() {
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// No clone occurs because `input` doesn't need to be mutated.
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let slice = [0, 1, 2];
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let mut input = Cow::from(&slice[..]);
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match abs_all(&mut input) {
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Cow::Borrowed(_) => println!("I borrowed the slice!"),
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_ => panic!("expected borrowed value"),
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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 reference_mutation() -> Result<(), &'static str> {
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// Clone occurs because `input` needs to be mutated.
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let slice = [-1, 0, 1];
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let mut input = Cow::from(&slice[..]);
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match abs_all(&mut input) {
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Cow::Owned(_) => println!("I modified the slice and now own it!"),
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_ => panic!("expected owned value"),
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Cow::Owned(_) => Ok(()),
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_ => Err("Expected owned value"),
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}
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}
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// No clone occurs because `input` is already owned.
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#[test]
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fn reference_no_mutation() -> Result<(), &'static str> {
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// No clone occurs because `input` doesn't need to be mutated.
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let slice = [0, 1, 2];
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let mut input = Cow::from(&slice[..]);
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match abs_all(&mut input) {
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// TODO
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}
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}
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#[test]
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fn owned_no_mutation() -> Result<(), &'static str> {
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// We can also pass `slice` without `&` so Cow owns it directly.
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// In this case no mutation occurs and thus also no clone,
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// but the result is still owned because it always was.
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let slice = vec![0, 1, 2];
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let mut input = Cow::from(slice);
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match abs_all(&mut input) {
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// TODO
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}
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}
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#[test]
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fn owned_mutation() -> Result<(), &'static str> {
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// Of course this is also the case if a mutation does occur.
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// In this case the call to `to_mut()` returns a reference to
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// the same data as before.
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let slice = vec![-1, 0, 1];
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let mut input = Cow::from(slice);
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match abs_all(&mut input) {
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// TODO
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Cow::Borrowed(_) => println!("I own this slice!"),
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_ => panic!("expected borrowed value"),
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}
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}
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}
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@ -13,3 +13,5 @@ the other useful data structure, hash maps, later.
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## Further information
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- [Storing Lists of Values with Vectors](https://doc.rust-lang.org/stable/book/ch08-01-vectors.html)
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- [`iter_mut`](https://doc.rust-lang.org/std/primitive.slice.html#method.iter_mut)
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- [`map`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.map)
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