Rust Brain Teasers/

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Puzzle 14: Explanation

Puzzle 14: Explanation

Let’s learn about how structured storage memory works in Rust.

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use std::mem::size_of;
struct VeryImportantMessage {
    _message_type : u8,
    _destination : u16
}
fn main() {
    println!(
        "VeryImportantMessage occupies {} bytes.", 
        size_of::<VeryImportantMessage>()
    );
}

Explanation

Both _message_type and _destination occupy one and two bytes of memory. So, why does VeryImportantMessage occupy four bytes of memory?

By default, Rust makes these two promises about the in-memory representation of structures:

  • Structures may be differently sized than their contents for performance reasons.

  • Structures may internally store data in a different order than we specified if the optimizer ...