Allocate array onto heap with size known at runtime

Question

In C++, I could put an array of 1000 ints onto the heap like this:

int size = 1000;
int* values = new int[size];
delete[] values;

I can't figure out how to do the equivalent in Rust.

let size = 1000;
let values = Box::new([0; size]) // error: non-constant path in constant expression

To my understanding, Rust forces the size of all arrays to be known at compile time and doesn't let you use expressions when creating arrays.

Answer 1

Arrays in Rust are fixed-length. If you want a dynamically-sized array, use Vec. In this case, the simplest way is with the vec! macro:

let size = 1000;
let values = vec![0; size];

Also, if you're super concerned about Vec being three words long and don't need to resize the storage after it's created, you can explicitly discard the internal capacity, and bring values down to two words on the stack:

let values = values.into_boxed_slice(); // returns a Box<[i32]>.