API Design Best Practices in Rust

Design your API using struct for data, impl blocks for methods, and Result<T, E> for error handling to ensure safety and clarity.

struct User {
    username: String,
    email: String,
}

impl User {
    fn new(username: String, email: String) -> Result<Self, String> {
        if username.is_empty() {
            return Err("Username cannot be empty".to_string());
        }
        Ok(User { username, email })
    }
}

This pattern uses the struct definition to group related fields, the impl block to define the new constructor, and returns a Result to handle validation errors explicitly.

Think of your API design as building a set of clear, labeled boxes (structs) with specific instructions on how to fill them (methods). You should always check if the instructions were followed correctly and report any mistakes immediately (using Result) so the user knows exactly what went wrong. This approach prevents confusing errors later and makes your code easier for others to use safely.