diff options
| -rw-r--r-- | exercises/smart_pointers/cow1.rs | 66 | ||||
| -rw-r--r-- | info.toml | 6 |
2 files changed, 49 insertions, 23 deletions
diff --git a/exercises/smart_pointers/cow1.rs b/exercises/smart_pointers/cow1.rs index 5fba251..885138a 100644 --- a/exercises/smart_pointers/cow1.rs +++ b/exercises/smart_pointers/cow1.rs @@ -4,6 +4,9 @@ // 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. // I AM NOT DONE @@ -20,29 +23,52 @@ fn abs_all<'a, 'b>(input: &'a mut Cow<'b, [i32]>) -> &'a mut Cow<'b, [i32]> { input } -fn main() { - // 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) { - Cow::Borrowed(_) => println!("I borrowed the slice!"), - _ => panic!("expected borrowed value"), +#[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"), + } } - // 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(_) => println!("I modified the slice and now own it!"), - _ => panic!("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 + } } - // No clone occurs because `input` is already owned. - let slice = vec![-1, 0, 1]; - let mut input = Cow::from(slice); - match abs_all(&mut input) { - // TODO - Cow::Borrowed(_) => println!("I own this slice!"), - _ => panic!("expected borrowed value"), + #[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 always was. + 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()` 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 + } } } @@ -1010,11 +1010,11 @@ https://doc.rust-lang.org/stable/book/ch16-00-concurrency.html [[exercises]] name = "cow1" path = "exercises/smart_pointers/cow1.rs" -mode = "compile" +mode = "test" hint = """ -Since the vector is already owned, the `Cow` type doesn't need to clone it. +If Cow already owns the data it doesn't need to clone it when to_mut() is called. -Checkout https://doc.rust-lang.org/std/borrow/enum.Cow.html for documentation +Check out https://doc.rust-lang.org/std/borrow/enum.Cow.html for documentation on the `Cow` type. """ |