Implementing a Trait Solver in Rust

This challenge asks you to implement a simplified trait solver in Rust. Trait solving is a crucial part of Rust's type system, determining which concrete types satisfy a given trait bound. This exercise will help you understand how Rust's compiler infers types and resolves trait implementations.

Problem Description

You are tasked with creating a function solve_trait that takes a trait name (represented as a &str) and a list of type names (also &str) as input. The function should return a Vec<&str> containing the names of the types that implement the specified trait. The trait and type names are strings. You will be provided with a hardcoded list of traits and their implementations. The solver should only return types that directly implement the trait, not those implementing it through inheritance or other mechanisms.

Key Requirements:

• The function must correctly identify types that implement the given trait.
• The function must return an empty vector if no types implement the trait.
• The function should handle invalid trait names gracefully (return an empty vector).
• The function should be efficient for the expected input sizes.

Expected Behavior:

The solve_trait function should iterate through the provided list of types and check if each type implements the specified trait. If a type implements the trait, its name should be added to the result vector.

Edge Cases to Consider:

• The trait name is not found in the hardcoded list of traits.
• The list of types is empty.
• The trait has no implementations.
• The trait name is an empty string.
• Type names are empty strings.

Examples

Example 1:

Input: trait_name = "Display", types = ["i32", "f64", "String", "bool"]
Output: ["i32", "f64", "String", "bool"]
Explanation: All the provided types implement the `Display` trait.

Example 2:

Input: trait_name = "Debug", types = ["i32", "f64", "String", "bool"]
Output: ["i32", "f64", "String", "bool"]
Explanation: All the provided types implement the `Debug` trait.

Example 3:

Input: trait_name = "Clone", types = ["i32", "f64", "String", "bool"]
Output: ["i32", "f64", "String", "bool"]
Explanation: All the provided types implement the `Clone` trait.

Example 4:

Input: trait_name = "Serialize", types = ["i32", "f64", "String", "bool"]
Output: []
Explanation: None of the provided types implement the `Serialize` trait.

Example 5:

Input: trait_name = "NonExistentTrait", types = ["i32", "f64", "String", "bool"]
Output: []
Explanation: The trait "NonExistentTrait" is not defined, so no types can implement it.

Constraints

• The number of types in the types vector will be between 0 and 100.
• Trait and type names are strings with a maximum length of 50 characters.
• The function should complete within 100ms for the given input sizes.
• The hardcoded trait implementations are provided as a constant within the code.

Notes

You can hardcode the trait implementations within your function. Consider using a HashMap or similar data structure to efficiently store and retrieve trait implementations. Focus on clarity and correctness over extreme optimization. The goal is to demonstrate understanding of trait solving concepts, not to build a full-fledged compiler. The trait names and type names are simple strings, so no complex parsing is required. The trait solver only needs to check for direct implementations, not inheritance.

fn solve_trait(trait_name: &str, types: &[&str]) -> Vec<&str> {
    // Hardcoded trait implementations (for simplicity)
    const IMPLEMENTATIONS: std::collections::HashMap<&str, Vec<&str>> = {
        let mut map = std::collections::HashMap::new();
        map.insert("Display", vec!["i32", "f64", "String", "bool"]);
        map.insert("Debug", vec!["i32", "f64", "String", "bool"]);
        map.insert("Clone", vec!["i32", "f64", "String", "bool"]);
        map
    };

    let mut result = Vec::new();

    if let Some(implementations) = IMPLEMENTATIONS.get(trait_name) {
        for &type_name in types {
            if implementations.contains(&type_name) {
                result.push(type_name);
            }
        }
    }

    result
}