Implement repr(C) Behavior in Rust

This challenge asks you to replicate the behavior of C's struct layout (repr(C)) within Rust. Understanding and controlling struct memory layout is crucial for interoperability with C code, performance-critical applications, and low-level systems programming.

Problem Description

Your task is to create a Rust struct that mimics the memory layout characteristics of a C struct. Specifically, you need to ensure that the fields of your Rust struct are laid out in memory consecutively and in the order they are declared, without any padding introduced by the Rust compiler for alignment purposes. This is analogous to using the #[repr(C)] attribute in Rust or how structs are typically laid out in C.

Key Requirements:

1. Sequential Field Layout: Fields must appear in memory in the same order they are defined in the struct.
2. No Compiler Padding: The Rust compiler should not insert any padding bytes between fields for alignment.
3. Size and Alignment: The total size and alignment of the struct should match what would be expected from a C compiler for a similar struct definition.

Expected Behavior:

When inspecting the memory representation of your struct, you should be able to directly map its fields to contiguous memory locations as defined. This is often verified by checking the size of the struct and the offsets of its fields.

Edge Cases:

• Consider structs with fields of varying sizes and alignment requirements.
• Think about how different primitive types and their potential alignments affect the overall layout.

Examples

Example 1: Imagine a C struct:

struct MyCStruct {
    char a;      // 1 byte
    int b;       // 4 bytes (assuming 32-bit int)
    short c;     // 2 bytes
};

In C, this might have a size of 7 bytes (1 + 4 + 2), or potentially more if padding is added for alignment of int. For repr(C) behavior, we aim for no padding.

Rust Input: A Rust struct definition that, when compiled and inspected, matches the C layout with minimal or no padding. For instance, a direct translation might be:

#[repr(C)] // You will implement this behavior manually, not use the attribute directly.
struct MyRustStruct {
    a: u8,
    b: u32, // Assuming 32-bit int in C, u32 in Rust
    c: u16,
};

Rust Output (Conceptual): The memory layout of MyRustStruct should be equivalent to the C struct, meaning the fields a, b, and c are laid out sequentially.

• a starts at offset 0.
• b starts at offset 1.
• c starts at offset 5. The total size would be 1 + 4 + 2 = 7 bytes, with no extra padding at the end.

Example 2: Consider a C struct with a different order:

struct AnotherCStruct {
    int x;       // 4 bytes
    char y;      // 1 byte
    short z;     // 2 bytes
};

A C compiler might pad y to align z, leading to a size larger than 7 bytes. For repr(C) behavior, we want sequential layout.

Rust Input:

// Equivalent Rust struct without #[repr(C)]
struct AnotherRustStruct {
    x: u32,
    y: u8,
    z: u16,
};

Rust Output (Conceptual):

• x at offset 0.
• y at offset 4.
• z at offset 5. Total size: 4 + 1 + 2 = 7 bytes.

Constraints

• Focus on primitive integer and character types (u8, i8, u16, i16, u32, i32, u64, i64, usize, isize, char).
• The solution should be idiomatic Rust, even though it's emulating C behavior.
• Performance considerations are secondary to correctness of memory layout.
• The implementation should be demonstrable by inspecting struct size and field offsets.

Notes

To verify your implementation, you will need to use Rust's std::mem::size_of to check the total size of the struct and std::mem::offset_of (available in nightly Rust or via a crate) to check individual field offsets. The goal is to achieve a layout identical to what #[repr(C)] would produce for the same fields. You are not allowed to use #[repr(C)] or #[repr(align(...))] attributes; you must achieve the layout through careful field ordering and potentially by using zero-sized types (ZSTs) if absolutely necessary, though ideally not. Consider the typical alignment rules of C for primitive types on common architectures when determining the expected layout.