How does Rust store enum values in arrays?

Question

The following is valid Rust:

enum Foo {
    One(i32, i32, i32),
    Two { x: i32, y: i32 },
}

fn main() {
    let x: [Foo; 2] = [Foo::One(1, 2, 3), Foo::Two         


        

Answer 1

Rust being a systems programming language, you can just ask it!

use std::mem;

enum Foo {
    One(i32, i32, i32),
    Two { x: i32, y: i32 },
}

fn main() {
    println!("{}", mem::size_of::());
}

This prints 16 on the playground.

And note that I did not specify whether I talked about One or Two, because it does not matter. Foo has a unique size.

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As a rule of thumb, you might want to avoid storing a very large variant. One solution, if a single variant is much bigger than the other, is to reach out to Box.