|
|
|
@ -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
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|