Rust: What is the difference between Cow and Arc?

Cow — clone-on-write. Arc — atomic reference counting.

Cow:

• Lazy cloning.
• Can be borrowed or owned.
• For conditional cloning.

Arc:

• Shared ownership.
• Atomic counting.
• For thread-safe sharing.

1use std::borrow::Cow;
2
3fn process(s: Cow<str>) {
4    // Clone only if modification needed
5}
6
7use std::sync::Arc;
8let shared = Arc::new(String::from("data"));
9let clone = Arc::clone(&shared);

Key: Cow for lazy cloning, Arc for shared ownership.