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Understanding Rust Error E0634: Conflicting Packed Representation Hints

What causes Rust Error E0634?

Rust Error E0634 occurs when a type has conflicting packed representation hints. `packed` and `packed(n)` attributes are used to specify the desired alignment or packing for the struct. This error is triggered when the hints are used with conflicting arguments, making it unclear how the struct should be packed.

Conflict in packed representation hints:

Consider the following erroneous code examples that trigger Rust Error E0634:

#![allow(unused)]
fn main() {
  #[repr(packed, packed(2))] // error!
  struct Company(i32);

  #[repr(packed(2))] // error!
  #[repr(packed)]
  struct Company(i32);
}

How to fix Rust Error E0634?

To resolve Rust Error E0634, choose a single packed hint for your type. If you want the struct to be tightly packed, use the `packed` attribute. If you want a custom packing, specify the desired size with `packed(n)`.

Correct usage of packed representation hints:

Here are some proper examples of using packed representation hints in Rust structs:

#![allow(unused)]
fn main() {
  #[repr(packed)] // ok!
  struct Company(i32);

  #[repr(packed(2))] // ok!
  struct Employee(u32, f32);
}

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