Implementing Tagged Pointers in Rust

Tagged pointers are a powerful technique used in memory management and concurrency to associate metadata with a pointer without requiring additional memory allocation. This challenge asks you to implement a basic tagged pointer system in Rust, allowing you to store a small tag alongside a raw pointer, enabling safer and more expressive memory operations. This is useful for scenarios like tracking ownership, identifying the source of a pointer, or implementing custom memory allocators.

Problem Description

You are tasked with creating a TaggedPointer<T> struct in Rust that encapsulates a raw pointer to data of type T and a tag (represented as a u32). The TaggedPointer should provide methods for:

1. Creation: A constructor that takes a raw pointer (*const T) and a tag (u32) and creates a TaggedPointer.
2. Accessing the Pointer: A method to retrieve the raw pointer (*const T).
3. Accessing the Tag: A method to retrieve the tag (u32).
4. Safety: The struct should be designed to prevent direct modification of the underlying raw pointer. It should be read-only.

The challenge focuses on the structural implementation and safe access, not on memory allocation or deallocation. Assume the raw pointer is valid at the time of TaggedPointer creation.

Examples

Example 1:

Input: let ptr = std::ptr::null(); let tag = 42u32; let tagged_ptr = TaggedPointer::new(ptr, tag);
Output: tagged_ptr.get_pointer() == std::ptr::null(); tagged_ptr.get_tag() == 42;
Explanation: A `TaggedPointer` is created with a null pointer and a tag of 42. The methods correctly retrieve these values.

Example 2:

Input: let data = [1, 2, 3]; let ptr = data.as_ptr() as *const i32; let tag = 10u32; let tagged_ptr = TaggedPointer::new(ptr, tag);
Output: tagged_ptr.get_pointer() == data.as_ptr() as *const i32; tagged_ptr.get_tag() == 10;
Explanation: A `TaggedPointer` is created with a valid pointer to an array and a tag of 10. The methods correctly retrieve these values.

Example 3: (Edge Case - Null Pointer)

Input: let ptr = std::ptr::null(); let tag = 0u32; let tagged_ptr = TaggedPointer::new(ptr, tag);
Output: tagged_ptr.get_pointer() == std::ptr::null(); tagged_ptr.get_tag() == 0;
Explanation:  Handles the case where the initial raw pointer is null.

Constraints

• The tag must be a u32.
• The TaggedPointer struct must be read-only. No methods should allow modification of the underlying pointer or tag after creation.
• The raw pointer T can be any valid type.
• The code must compile without warnings.

Notes

• Consider using std::ptr::null() to represent a null pointer.
• Rust's ownership and borrowing system should be leveraged to ensure safety.
• Focus on the structure and methods of the TaggedPointer struct. You do not need to implement any memory allocation or deallocation logic.
• Think about how to prevent accidental modification of the raw pointer. Using *const T is a good starting point.
• The goal is to create a safe and convenient way to associate a tag with a raw pointer.