49 lines
1.5 KiB
Rust
49 lines
1.5 KiB
Rust
// 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"),
|
|
}
|
|
}
|