Rust: argument requires that borrow lasts for `'static` - rust

Question

I'm doing some exercises with using threads in Rust. I want to print chunked string, but I can't get pass lifetimes issue I've stumbled upon. Here's my code:
let input = "some sample string".to_string();
let mut threads = vec![];
for chunk in input.chars().collect::<Vec<char>>().chunks(2) {
threads.push(thread::spawn({
move || -> () {
println!("{:?}", chunk);
}
}))
}
When I'm trying to run it, I get a following error:
error[E0716]: temporary value dropped while borrowed
--> src\main.rs:7:18
|
7 | for chunk in input.chars().collect::<Vec<char>>().chunks(2) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^----------
| | |
| | temporary value is freed at the end of this statement
| creates a temporary which is freed while still in use
| argument requires that borrow lasts for `'static`
I understand that the compiler doesn't know if the chunk within the thread will not outlive the input variable. But what I can do to fix this code?
I've tried to clone() the vector, but it didn't help.

Answer 1

The chunks are of the type &[char], with the same lifetime as the string.
Simply cloning here won't work, as at compile time it doesn't know the size of the char array. To get a owned copy of a unknown sized array, you must convert it to a Vec, which is done easily with the to_vec() function.
let input = "some sample string".to_string();
let mut threads = vec![];
for chunk in input.chars().collect::<Vec<char>>().chunks(2) {
let owned_chunk = chunk.to_vec();
threads.push(thread::spawn({
move || -> () {
println!("{:?}", owned_chunk);
}
}))
}
Alternatively, since we know the size of the array, we can create an array on the stack to copy into. This removes the need to allocate any heap memory.
let input = "some sample string".to_string();
let mut threads = vec![];
for chunk in input.chars().collect::<Vec<char>>().chunks(2) {
let mut owned_array = ['\0'; 2];
owned_array.copy_from_slice(chunk);
threads.push(thread::spawn({
move || -> () {
println!("{:?}", owned_array);
}
}))
}