Do you know its size?

What this Rust memory-layout interview question tests

This is a medium-difficulty question that probes your understanding of how Rust represents types in memory on a 64-bit system. It rewards precise knowledge of struct layout, alignment, and size rather than guesswork, and is the kind of question that separates candidates who have worked with Rust's type system from those who have only skimmed the surface.

To answer correctly, you need to reason about how the Rust compiler allocates space for types—including padding for alignment, the size of primitive types on 64-bit platforms, and how struct fields are arranged. This matters in systems programming and performance-sensitive contexts where memory layout directly affects cache behavior and binary size.

• Alignment and padding rules in Rust
• Size of primitive types on 64-bit architectures
• How the compiler orders and packs struct fields
• The std::mem::size_of function and related introspection