Warn about using Arc::new() when using the vec![value; size] macro. #8719
Description
What it does
This lint would warn against using Arc::new in the vec![value; size] macro, because it computes the value once and then clones the value size times instead of generating a new Arc each of the size times.
If the user truly wants a vector of Arcs all pointing to the same arc, then they should make that obvious by constructing the arc before constructing the vector.
Lint Name
No response
Category
No response
Advantage
No response
Drawbacks
No response
Example
#[test]
fn unexpected_vec_macro_behavior() {
let v = vec![Arc::new(Mutex::new(0usize)); 100];
*v[0].lock().unwrap() = 20;
*v[1].lock().unwrap() = 30;
assert_eq!(*v[0].lock().unwrap(), 20);
}Could be written as:
#[test]
fn vec_behavior_is_more_obvious() {
let cloned_arc = Arc::new(Mutex::new(0usize));
let v = vec![cloned_arc; 100];
*v[0].lock().unwrap() = 20;
*v[1].lock().unwrap() = 30;
assert_eq!(*v[0].lock().unwrap(), 30);
}