CODEWITHSUNDEEP
syntaxrustinitialization
Michał Fita
Michał Fita

Reputation: 1329

How to partially initialize an ArrayVec?

I need structures with fixed maximum size, so the obvious choice seem to be arrayvec crate. However, I'm stuck when ArrayVec is a member of a structure that later needs to be partially initialised:

use arrayvec::ArrayVec; // 0.4.7

#[derive(Debug)]
struct Test {
    member_one: Option<u32>,
    member_two: ArrayVec<[u16; 5]>,
}

pub fn main() {
    let mut test = Test {
        member_one: Some(45678),
        member_two: [1, 2, 3], // <- What to do here to initialise only 3 elements?
    };

    print!("{:?}", test);
}

I'd like to initialise the first three elements of the ArrayVec as it's perfectly capable of holding any number of elements from zero to 5 (in my example), but I can't figure out how to do it.

Upvotes: 1

Views: 288

Answers (2)

Peter Hall
Peter Hall

Reputation: 58735

You can collect into an ArrayVec from an iterator:

let mut test = Test {
    member_one: Some(45678),
    member_two: [1, 2, 3].into_iter().collect(),
};

Upvotes: 3

Shepmaster
Shepmaster

Reputation: 430961

ArrayVec does not offer a one-step method to do this. Instead, create the ArrayVec and then add values to it, in any of the ways you can add values: 

let mut member_two = ArrayVec::new();
member_two.extend([1, 2, 3].iter().cloned());
let test = Test {
    member_one: Some(45678),
    member_two, 
};

Upvotes: 1

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