How to initialize a large array with a single value?

Question

I am trying to implement Atkin's sieve in Rust. This requires initializing an array with false. The syntax for this on the internet no longer works.

fn main() {
    const limit:usize = 1000000000;
    let mut sieve:[bool; limit] = [false];
}

I expect this to create an array of size limit filled with false, instead

rustc "expected an array with a fixed size of 1000000000 elements, found one with 1 element".

jfMR · Accepted Answer · 2021-04-10 16:59:41Z

11

[false] is an array with one element, i.e., its type is [bool; 1].

What you want is [false; limit] instead of [false]:

fn main() {
    const limit: usize = 1_000_000_000;
    let mut sieve = [false; limit];
}

There is no need for the type annotation [bool; limit] here as it can be inferred.

answered Apr 10, 2021 at 16:59

jfMR

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