No you're just making stuff up. https://doc.rust-lang.org/nomicon/repr-rust.html https://doc.rust-lang.org/nomicon/repr-rust.html The bulk of this section is

No you're just making stuff up. https://doc.rust-lang.org/nomicon/repr-rust.html https://doc.rust-lang.org/nomicon/repr-rust.html The bulk of this section is describing how Rust has reserved the right to reorder and pack stuff. The first example happens to be 32-bit aligned because it contains a value that is.