memory-layout

memory-layout is a minimal no_std compatible crate that allows you to specify the memory layout of a struct, similarly to C#'s [StructLayout(LayoutKind.Explicit)].

Docs

https://docs.rs/memory-layout/

Features

• Specify the offset a field should have in a struct.
• Offsets are checked to be valid at compile time.
• no_std compatible.

Example

use memory_layout::memory_layout;

#[memory_layout]
pub struct Example {
  #[field_offset(0x00)]
  a: i32,
  #[field_offset(0x10)]
  b: u64,
  #[field_offset(0x20)]
  c: f32
}

Will expand to:

#[repr(C, packed)]
pub struct Example {
  #[doc(hidden)]
  __pad0: [u8; 0usize],
  a:      i32,
  #[doc(hidden)]
  __pad1: [u8; 16usize - ::core::mem::size_of::<i32>()],
  b:      u64,
  #[doc(hidden)]
  __pad2: [u8; 8usize - ::core::mem::size_of::<u64>()],
  c:      f32
}

Caveats

• Fields have to be defined in ascending order by the specified offset.
• #[memory_layout] attribute has to be defined before any derive attributes.
• repr(C, packed) is forced.
• Does not ensure valid field alignment (more info).

Comparable projects

struct_layout

This project has a similar goal to this crate, replicating C#'s [StructLayout(LayoutKind.Explicit)]. The key difference is that struct_layout uses an internal array that can be accessed using methods like get_<field_name> and set_<field_name> while this crate aligns the fields themselves.