Implementing Basic Monomorphization in Rust

Monomorphization is a powerful optimization technique where the compiler generates specialized versions of a generic function or struct for each concrete type it's used with. This eliminates the overhead of dynamic dispatch and often results in significantly faster code. This challenge asks you to implement a simplified version of monomorphization to understand the underlying principles.

Problem Description

You are tasked with creating a system that manually performs monomorphization for a simple generic function. The function process_data takes a slice of data and a processing function. Your system should analyze the types used with process_data, generate specialized versions of process_data for each unique type, and then select the appropriate specialized version at compile time. Essentially, you'll be creating a macro that expands into different code paths based on the type of the input slice.

What needs to be achieved:

1. Define a generic function process_data<T, F>(data: &[T], processor: F) -> i32 where F is a trait with a single method process(value: &T) -> i32.
2. Create a macro monomorphize_process that takes the trait F as a parameter.
3. The macro should generate a separate process_data function for each concrete type T used with the original process_data function. For simplicity, we'll only consider i32 and f64 as possible types for T.
4. The macro should also generate a dispatch function that selects the correct process_data implementation based on the type of the input slice.

Key Requirements:

• The macro must generate distinct process_data functions for i32 and f64.
• The dispatch function must correctly call the appropriate process_data implementation based on the type of the input slice.
• The generated code should be functionally equivalent to the original generic process_data function, but with specialized implementations for i32 and f64.

Expected Behavior:

When the macro is used, the compiler should generate two specialized process_data functions: one for i32 and one for f64. The dispatch function should then select the correct version at compile time, avoiding any runtime overhead.

Edge Cases to Consider:

• What happens if a type other than i32 or f64 is used with the macro? (For this simplified version, you can assume only i32 and f64 will be used.)
• How to ensure the generated functions have the correct signature?

Examples

Example 1:

Input:
trait Processor {
    fn process(&self, value: &i32) -> i32;
}

struct MyProcessor;
impl Processor for MyProcessor {
    fn process(&self, value: &i32) -> i32 {
        *value * 2
    }
}

monomorphize_process!(Processor);

fn main() {
    let data: [i32; 3] = [1, 2, 3];
    let processor = MyProcessor;
    let result = process_data(&data, processor);
    assert_eq!(result, 6);
}

Output: The code compiles and runs, producing the result 6. The compiler generates specialized process_data functions for i32.

Explanation: The macro generates a process_data function specifically for i32 slices. The main function then calls this specialized version, resulting in the correct calculation.

Example 2:

Input:
trait Processor {
    fn process(&self, value: &f64) -> i32;
}

struct MyProcessor;
impl Processor for MyProcessor {
    fn process(&self, value: &f64) -> i32 {
        (*value as i32)
    }
}

monomorphize_process!(Processor);

fn main() {
    let data: [f64; 3] = [1.0, 2.0, 3.0];
    let processor = MyProcessor;
    let result = process_data(&data, processor);
    assert_eq!(result, 6);
}

Output: The code compiles and runs, producing the result 6. The compiler generates a specialized process_data function for f64.

Explanation: The macro generates a process_data function specifically for f64 slices. The main function then calls this specialized version, resulting in the correct calculation.

Constraints

• The macro must only generate specialized functions for i32 and f64.
• The trait F must have a single method process(value: &T) -> i32.
• The generated code must be valid Rust code.
• The solution should be reasonably efficient (avoid unnecessary code generation).

Notes

• This is a simplified version of monomorphization. Real-world monomorphization is much more complex and handles a wider range of types and scenarios.
• Consider using Rust's macro system to generate the specialized functions and the dispatch function.
• Think about how to ensure that the generated functions have the correct signature and are called with the correct arguments.
• The goal is to understand the concept of monomorphization, not to create a production-ready implementation. Focus on clarity and correctness over extreme optimization.
• You'll need to define a trait for the processor function.