diff options
| -rw-r--r-- | exercises/standard_library_types/cow1.rs | 48 | ||||
| -rw-r--r-- | info.toml | 11 |
2 files changed, 59 insertions, 0 deletions
diff --git a/exercises/standard_library_types/cow1.rs b/exercises/standard_library_types/cow1.rs new file mode 100644 index 0000000..5fba251 --- /dev/null +++ b/exercises/standard_library_types/cow1.rs @@ -0,0 +1,48 @@ +// 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. + +// 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 +} + +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"), + } + + // 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"), + } + + // 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"), + } +} @@ -932,6 +932,17 @@ is too much of a struggle, consider reading through all of Chapter 16 in the boo https://doc.rust-lang.org/stable/book/ch16-00-concurrency.html """ +[[exercises]] +name = "cow1" +path = "exercises/standard_library_types/cow1.rs" +mode = "compile" +hint = """ +Since the vector is already owned, the `Cow` type doesn't need to clone it. + +Checkout https://doc.rust-lang.org/std/borrow/enum.Cow.html for documentation +on the `Cow` type. +""" + # THREADS [[exercises]] |